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THE JOURNAL 


OF 


THE DEPARTMENT OF AGRICULTURE 


OF 


PORTO RIGO 


Vou. IV 








THE MOTTLING OR YELLOW STRIPE DISEASE OF 
SUGAR-CANE. 


By JoHN A. STEVENSON. 
INTRODUCTION. 


The epidemic of cane disease which has prevailed in the Island 
through several seasons has continued with unabated severity. Not 
only has the disease not shown any decrease in virulence in the dis- 
tricts formerly reported as infected but has spread into new areas, 
and is here likewise causing heavy losses. It seems certain that the 
portions of the Island as yet free of infection will, before another 
has passed, fall prey to the ravages of this disease. 

Studies as outlined in a previous report (31)! have been continued 
as vigorously as circumstances permitted, and it is felt that satis- 
factory progress has been made toward an understanding of the 
problems involved. It has been necessary to still further alter views 
previously held as to the nature of the disease involved. As a re- 
sult of experimental and field data obtained it has become quite 
clear that mottling cannot be considered as a form of degeneration 
and that it is an infectious disease. 


A complete discussion of all phases of the problem, covering the 
work of practically three seasons, follows in the body of this paper, 
and will form a final report by the writer on the mottling disease 


of cane. 


1 Figures in parenthesis refer to literature cited on p. 66. 

Norre.—Credit is due Mr. E. D. Colén, now Director of the Insular Experiment Station 
of the Department of Agriculture of Porto Rico; to Mr. R. C. Rose, formerly first assistant 
pathologist, and to Mr. Bernardo Lépez, assistant, division of plant pathology and botany 
for assistance in the work of obtaining field data and other information. Favors extended 
bv officials of the South Porto Rico Sugar Co. have aided in the prosecution of the work. 

3 





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YELLOW STRIPE OF SUGAR-CANE. 


NAME OF THE DISEASE, 


Various names have been applied to this malady. It is univer- 
sally known among the planters as la enfermedad (the disease) 
all other cane diseases of their experience sinking into insignificance 
in comparison with it. Of late it has also been called in popular 
accounts mordida de perro. The writer has referred to it at va- 
rious times as the ‘‘new disease, the mottling disease, and cane 
canker,’’ but considers the term mottling disease more nearly de- 
scriptive than any other, and therefore preferable. This name was 
definitely proposed in the 1916-17 report. 

Cane canker is not considered suitable since the canker stage is 
not always present. Chlorosis, which might be used, and in fact 
was used to some extent, is pre-empted by a very different type of 
non-parasitic disease occurring in limited areas on the south coast. 
Prot. Earle (9) has recently used the term mosaie? which has nothing 
to recommend it in preference to mottling. Mr. Colén in the same 
paper refers to the disease as yellow-striping or enfermedad de las 
rayas amarillas. This is hardly suitable since it is not descriptive 
of the disease on the one hand and on the other will cause confusion 
with the natural phenomenon of yellow striping so common in eer- 
tain varieties of cane, particularly the dark red, and which is a non- 
parasitic phenomenon of the class referred to by plant breeders as 
chimeras. 

DISTRIBUTION. 


The disease has made very definite and rapid progress during 
the time it has been under observation. At the end of the first 
season’s studies as noted in the 1915-16 report (26), it had attacked 
the cane in the region bounded by Aguadilla to the west and a line 
from Utuado to Arecibo, or along the valley of the Arecibo River, 
on the east. Lack of time did not then permit the working out of 
more exact boundaries, particularly along the south and west. 

The approximate extent of territory covered by the disease up 
to July 1, 1916, is shown by the dotted line on the map (Fig, 1). 
The area already covered at this time indicates that the disease had 
been active for some years at least, and it is not impossible that it 
had been present for a much longer time as a minor trouble in the 
upland fields beyond the coastal plain. Some planters have declared 
that the disease has been known to them for many years, and others 
are equally confident that it is an entirely new proposition. Be- 
54 meme mammeaed and used by Mr. F. S. Earle, Specialist on Cane Diseases, Insular 


Experiment Station, because it at once indicates what he believes it to be the nature and 
relationship of the disease.—EDiTOR. 








6 JOURNAL OF THE DEPARTMENT OF AGRICULTURE. 


‘cause of the ease with which the mottling is confused with other 
cane diseases and abnormalities such as yellow spotting, chlorosis, 
striping, and others discussed further on in this paper, it is im- 
possible to arrive at any conclusion, based on information obtainable 
to date, as to when it was first introduced to the Island. 

During the remainder of 1916, and throughout the time since 
then the disease has made continuous and extremely rapid progress. 
The broken line on the map indicates the area covered up to the 
date of the last report (31) preceding the present one, as far as 
data was available. 

It will be noted that it had by this time occupied at least half 
the extent of the Island, having advanced a considerable distance to 
the east, and reached a point south of San German on the west. In 
commenting on the spread of the disease for the 1916-17 season it 
was noted ‘‘that the trouble has been largely confined to the upper 
reaches of the river valleys, to small enclosed inland valleys, and 
practically to fields among the foothills. The broad stretches of the 
coastal plain, but little above sea level, are still free or comparatively 
free of disease. Near Arecibo many of the lowland fields show on 
the average one per cent of mottled stools, but farther east, in the 
lowlands of the Plazuela Sugar Company,’ it was impossible to find 
a single diseased stool, although mottling commenced the instant 
the foot-hill formation began. This state of affairs was hardly to 
be expected, if the cause is parasitic, since these lowland fields are 
planted to susceptible varieties and form great continuous areas, 
often extending for miles in unbroken stretches.’’ 

This state of affairs has continued in large part to date, infee- 
tion not being uniform and continuous in these lowland tracts. It 
has been possible in specific cases to trace the source of infection to 
use of diseased seed rather than to natural agencies where serious 
amounts of disease have been found. 

At the present writing (November, 1918) the disease has covered 
over three-fourths of the Island as shown by the solid line on the 
map (Fig. 1). The disease-free area now includes only the cane- 
growing regions of the coast from San Juan to Fajardo, and those 
from Fajardo to the south as far as Central Fortuna.? To the west 
of San Juan the coastal area is comparatively free of mottling as 
far as inspections have been carried, but indications point to a serious 
outbreak here before another season has passed. Isolated infections 


1These lowlands are at present infested also.—EDITOR. 

? Outbreaks of mottling have been reported recently at various places between Central 
Fortuna, near Ponce and Central Lafayette, near Arroyo, as well as in the Fajardo and 
Naguabo districts.—EDITOR. 








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YELLOW STRIPE OF SUGAR-CANE. 7 

have been located at several points in the eastern sections, from 
which beyond much doubt the remainder of the territory will be 
speedily attacked. It is interesting to note that the inland valley 
districts of Caguas, Juncos, Cayey and Utuado are seriously in- 
fected, even though practically isolated. The cane fields around 
Utuado have been diseased for at least four seasons, but those of 
the other three districts had been free until within a year. This 
bears out the statement made in the previous report (31) concerning 
the manner of progress of the disease. 

‘‘In its eastward course the disease has apparently jumped from 
valley to valley, or has appeared spontaneously at many points some 
distance back from the ocean, rather than working along through 
the continuous coastal fields and then up each successive valley. It 
has almost universally evinced a marked preference for upland fields, 
in spite of the fact that they do not form the continuous areas so 
characteristic of the lowland country. Not only are these fields them- 
selves broken up by the numerous small hills, but the many valleys 
large and small are separated by extensive ridges and chains of 
hills.’’ 

In the original center of the infection area from Arecibo to Agua- 
dilla, the disease has continued severe where cane has been planted, 
but there was a general movement in this region to abandon cane 
in favor of tobacco and other minor crops. 

The situation at Utuado remains unchanged with fifty to one 
hundred per cent of infection, and the same conditions prevail in 
the neighborhood of Adjuntas. 

From Aguadilla southward there is probably not a field which 
will not show from one to fifty per cent of infection. Here again 
the disease was first noted and first caused serious loss in the up- 
lands but has now spread throughout all fields. In fact reports 
from the Aguadilla-Aguada district (Central Coloso) were to the 
effect that there was less disease during the season just past in the 
uplands than in the lower lying fields. Such field observations as 
time permitted seemed to verify this conclusion, but it can doubtless 
be explained by the fact that the upland fields, after being aban- 
doned to the disease the year before, were given thorough cultivation 
and replanted with selected seed, while the lowland fields were being 
ratooned. 

The cane fields of the entire southwest section of the Island are 
in what might be termed the second phase of the disease in which 
a decrease in yield is becoming very apparent. A year ago only 
very slight infections were noted, less than one per cent in the aggre- 














8 JOURNAL OF T'HE DEPARTMENT OF AGRICULTURE. 
gate, and many fields were entirely free of mottling. During the past 
season practically every field has become infected to a varying ex- 
tent, and there is every indication that serious losses will be sustained 
in the coming crop. 

Along the south coast the disease has advanced to the east be- 
yond Ponce as far as Fortuna. It is particularly serious in the 
neighborhood of Pefiuelas to the west of that city, as well as in the 
cane growing sections immediately adjoining it. 

There is every indication that in the coming season the disease 
will continue to a successful conclusion its conquest of the cane fields 
of the Island, since only a comparatively small section remains and 
this already has several known points of infection. 


AMOUNT AND NATURE OF THE LOSSES. 


It is difficult to arrive with any degree of accuracy at the losses 
sustained by the cane growers as a result of the ravages of this dis- 
ease, because of the great variation in amount and severity of in- 
fection from field to field. In last year’s report an estimate of 
$500,000 loss for the season was made and this was considered 
conservative. 

A comparison of sugar statistics for two seasons past will give 
some measure of the loss sustained. The 1917 crop as reported by 
the Bureau of Property Taxes of the Treasury Department was 
503,081 tons of sugar, while that of 1918 fell off to 453.795 tons. This 
shows a decrease of 49,286 tons with a value of over $5,000,000 figur- 
ing sugar at $5.27 per hundredweight, the average price for the 
season. Not all of this loss, however, can be charged to the mottling 
since the weather in certain sections and particularly in some where 
the disease had not penetrated, was such as to cause a heavy falling 
off in yield. A comparison of the output of the centrals (factories) 
of the Island for the two years makes it appear that at least half 
of this disease may be charged to the disease making the loss for 
1918 $2,500,000. 

Comparable results cannot be obtained by a study of the statis- 
tics for earlier years since economie conditions have been such as 
to cause great variation in the amount of cane planted, independent 
of natural factors. In the last two,seasons, however, the area planted 
has been practically uniform except as influenced by the disease. 

If to the figure $2,500,000, the estimated loss for 1918, there be 
added $500,000 for 1917, and the same amount for all previous years 
(but 1916 for the larger part), we reach a total of $3,500,000 loss 
to the sugar industry of Porto Rico to date. 








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YELLOW STRIPE OF SUGAR-CANE. 9 


The loss as heretofore has fallen heaviest on certain north coast 
mills. Several not before affected have suffered appreciably in the 
crop just past and there has been no improvement in the output of 
those which bore the brunt of the attack last year. One case in par- 
ticular may be mentioned where the production for the year was 
only half that of the previous season, due without any question to 
the effects of mottling. Another central reported a loss of nearly 
eight thousand tons, again entirely chargeable to the same cause. 
At least ten other sugar companies have a falling off of from five 
hundred to three thousand tons each which ean not be attributed 
to drought or environmental factors. 

Many of the colonos (growers who sell their cane to the centrals) 
and more especially those in the Arecibo-Aguadilla region where the 
disease first attracted attention, have been forced out of cane growing 
and have taken up tobacco, or other less remunerative crops. Their 
number is rapidly increasing. The adjustment necessary to the grow- 
ing of new crops entails no little loss under present economic con- 
ditions with greater liability of failure because of unfamiliarity with 
cultural conditions. : 

To turn to the nature of the losses incurred. As will be noted 
from the discussion under symptoms the losses result primarily from 
a decrease in tonnage. In the very early stages of infection it is 
not apparent to the observer that there is any reduction in yield or 
amount of sugar present in the juice. Exact experiments have noi 
been carried out locally to test this point, but an experiment per- 
formed by Lyon (20) of the Hawaiian Sugar Planters’ Experiment 
Station with a disease called by him vellow-striping, which is similar 
in nature to mottling, gives an exact idea of the reduction in ton- 
nage and sugar content. 

‘The experiment, planted in eight 80-ft. rows was arranged as 
follows: 

Rows 1 and 8, outside, blanket rows. 

Rows 2, 4 and 6 euttings from healthy canes. 

Rows 3, 5 and 7 euttings from canes having yellow stripe disease. 


“Two cuttings of three eyes each were taken from the top of 
each stick. All of the cuttings were carefully inspected to see that 
each had three perfect eyes. Sixty cuttings, thirty top and thirty 
second, were planted in each row, the top and second cuttings being 
similarly placed in each row, 

‘“‘The euttings from sound and diseased canes sprouted equally 
well and gave what appeared to be a uniform stand of cane. Not 































10 JOURNAL OF THE DEPARTMENT OF AGRICULTURE. 


a single stick tasseled in the experiment during the winter of 1912-13, 
but most of them tasseled in November, 1913. 

“‘The cane was cut during the last week in February, 1914, giv- 
ing the following results: 

‘‘From healthy cuttings, rows 2, 4, and 6— 


Healthy canes __-----_-----------. 430 weighing 3, 991.0 Ibs. 
Diseased canes__---- nee ene ree 81 weighing 693.5 Ibs. 
Undetermined canes..__....._.---_-_- 137 weighing 887.5 Ibs. 
Total millable canes___-__.---~-_- 648 weighing 5,572.0 Ibs. 
PRON RANE ee eo a ---- 187 weighing 553.5 Ibs. 


‘‘From diseased cuttings, rows 3, 5, and 7— 


TROAMNY HONOR 2 oo oe ee. 3 weighing 28.0 Ibs. 
ROSNONNOG ORION 6 6. oie nh 335 weighing 2, 683.5 Ibs, 
Undetermined canes _---__--__---_- 75 weighing 387.5 Ibs. 
Total millable canes._--_.__.______-_- 432 weighing 3, 099.0 Ibs. 
Dead ‘canos._......... eRe oe ape 210 weighing 534.5 Ibs. 


‘* Juice samples were obtained by grinding the cane from corre- 
sponding sections in the centers of two rows. The analyses were 
as follows: 

From healthy canes __--- Brix 20. 3, sucrose 19.07, purity 93.9 


From diseased canes___-- Brix 20.1, sucrose 19.11, purity 95.1 


‘‘The yields per acre computed from the above data would be: 


Healthy canes _.--_------ 101.13 tons cane, 14.98 tons sugar. 
Diseased canes__________- 56.24 tons cane, 8.43 tons sugar. 
Cen ee ee ea 44.89 tons eane, 6.55 tons sugar. 


‘*When comparing these yields it should be noted that twelve 
per cent of the canes from healthy cuttings became diseased during 
their growth so that the yield from healthy cuttings was thereby 
somewhat reduced.’’ 

As the disease progresses and during the second year of its pres- 
ence as a general rule, there is a very marked falling off in the yield, 
which may vary anywhere from twenty to one hundred per cent. 
From this stage on there is also an accompanying decrease in the 
amount of juice in the canes. The final stage in which no merchant- 
able cane is produced and the field is abandoned may occur the 
second year, but more commonly during the third, or on the second 
‘atoon. Hundreds of acres have reached this stage and thousands 


more are approaching it. 
In the severely diseased stalks of this latter stage (those showing 
eankering and splitting) there is not only the reduction in size and 

















YELLOW STRIPE OF SUGAR-CANE. ; 11 


the dry pithy condition due to a lack of juice, but what juice is 
present is highly objectionable from the viewpoint of the mill. Sev-’ 
eral mills have reported a high and therefore undesirable glucose 
ratio with correspondingly low sucrose, but other tests have not subs- 
tantiated this. The length of time between cutting and milling may 
well account for this in the instances reported, due to the cracked, 
cankered condition of the canes, which exposed the sugar containing 
tissues to the action of the air and fermenting organisms. 

Some further data along this line will be found under the head- 
ing ‘‘Chemical tests of the juice.’’ 


RATE AND MANNER OF SPREAD. 


The rate of spread in general as applied to the entire Island has 
already been given. To obtain a more detailed idea of the rate and 
manner of spread careful notes were kept on the progress of the 
disease in several fields near Rio Piedras. As this was an isolated 
infection area, no other diseased cane having been found within at 
least ten miles until very recently, the data obtained illustrates the 
manner of spread from a single infection. 

About 1915 a small planting (several rows) of Penang cane, 
the seed for which had been brought from near Aguadilla, was made 
as part of a variety experiment. The experiment after two seasons 
was transferred to another field with the exception of the Penang, 
which had practically died out. This condition had not been called 
to the writer’s attention and it cannot be definitely stated that mot- 
tling was the cause of the trouble, although all evidence points to 
that eonclusion. The field was not examined until after it had been 
plowed but several volunteer cane shoots, well marked with the dis- 
ease, found some weeks later confirmed this opinion. Field men 
after having been shown characteristic specimens agreed that the 
disease had been present on the variety in question. 

In the second field mottling was not noted until several months 
after planting, when infected stalks of B-3922 were found. As this 
variety had adjoined the Penang in the first test it seemed reasonable 
that a transfer had taken place at that point and that diseased seed 
had subsequently been planted in the second field. Infected stools 
were marked as they were found and their behavior during the season 
watched, stool to stool search being made at intervals. It was par- 
ticularly desired to ascertain the age at which cane was susceptible 
to attack as well as the rapidity with which it spread from. stool 
to stool. 








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YELLOW STRIPE OF SUGAR-CANE. 13 


The following table gives the number of diseased stalks found in 
each stool throughout the season: 


Table I.—Occurrence of Diseased Stalks. 





DATE OF OBSERVATION 
Stool No = ss se ae a 


May 16 June Il June 23 July 10 July 50 Angust 17!) Sept, 20 
a 3 2 8 ; 3 1 1 
or ceekeeenens 7 & 8 & 6 5 1 
Bi sig caaark teens 4 12 13 1 13 10 10 
* I 1 1 ! I 1 1 
Senne 2 3 3 3 
6 » ” » 2 9 9 
Rat exiale goers sisieis 1 1 8 3 3 
8. 14 13 11 10 8 8 
Wiis 5 5 i 3 3 
We io hecas ‘ 5 ; ? 1 2 
I : 2 l ? 2 2 2 
|) COURT Saat Eo ee i] 10 6 ( 6 6 
13 ) 6 7 ) 6 6 6 
lt ! 1 1 1 1 1 1 
15 I) | | i 7 6 5 
Be ecaias 6 6 i j 4 3 
17 ( 6 4 i 1 1 
WM ines LichA Seki iat Hepes ae fleeess conee doen 1 1 1 
19 3 1 5 





It will he noted that there was comparatively little change, a 
number ef weaker suppressed stelks dying, and a few additional ones 
developing the characteristie symptoms. As near as could be as- 
certained the mottled shoots in each stool arose from seedpieces other 
than these producing the normal shoots which predominated in 
nearly all the stools. Four seed pieces were planted in each hole, 
their combined stalks making up the stool. 

Several other stools in adjoining varieties showed mottling during 
the season as noted on the chart. (Fig. 2.) The results obtained 
here, combined with a series of field observations, make it evident 
that the bulk of infection occurs in young plants. 

At the end of the season all diseased stalks (none had shown 
cankering or other abnormalities beyond the leaf signs) were cut 
and destroyed. When the first ratoon shoots had reached approxi- 
mately a foot in height, an attempt was made to eradicate the disease 
from the field, sufficient evidence having been obtained by that time 
of the ability of the disease to spread by other means than infected 
seed pieces. Six times during the season the entire field was gone 
over and all mottled canes dug out and destroyed. The first time 
over the field only stalks actually showing signs of the disease were 
removed with the corresponding rhizome and root portions. In 
every case, however, the disease reappeared in these stools necessi- 
tating further removal. This indicates that where eradication work 














14 JOURNAL OF THE DEPARTMENT OF AGRICULTURE. 


is attempted the entire stool must be removed even though but a 
portion of the stalks composing it show actual signs of mottling. 

Wherever possible the stools were dug out carefully and search 
made for mottled and normal appearing shoots on the same rhizome. 
About twenty such cases were found in the course of the season and 
in each case a planting was made in the plant house of a portion 
of the apparently normal stalk. All of these, at a time varying 
from germination to several months later, produced leaves with thie 
characteristic markings. It was very clear that once infection oc- 
curred the virus or infecting principle spread through all parts of 
the plant, even though it might not be apparent in all the stalks. 

This eradication experiment will be further discussed under con- 
trol measures. 


OCCURRENCE OF THE DISEASE IN SANTO DOMINGO AND ELSEWHERE. 


The presence of very pronounced mottling on recently germinated 
Crystallina cane, the seed for which had been imported from Santo 
Domingo, made it evident that the disease also occurred in that 
island. In order to investigate the nature of its behavior there, 
and with the hope of obtaining other information of value, this island 
was visited in the course of the year. The results of this trip as 
given in a report prepared at the time are as follows in so far as 
they apply to the mottling: 

‘‘The first case (mottling) was found in the fields in the vicinity 
of Higueral, north of La Romana. The disease was present in prac- 
tically all fields varying in amount from a few scattered stools to 
as high as thirty per cent. The variety of cane was Crystallina. 
Symptoms of the disease, while characteristic, were limited to the 
mottling of the leaves. No evidences were seen of any stalks bearing 
the canker stage, in which the disease has proven so destructive in 
Porto Rico. Taken as a whole the cane in this district (Central 
Romana) appeared to be in fine condition, the presence of mottling 
having no appreciable effect on its growth. 

‘‘The disease was again encountered at Samana in small plant- 
ings, the seed for which had been brought from San Pedro de Ma- 
coris in the year previous. This latter fact makes it quite evident 
that the disease also exists in the extensive plantings at Macoris 
although no opportunity was had for a personal examination at that 
place. 

‘Only very small plots of cane were found at San Francisco 
de Macoris and these were free of the disease. Similarly at Cabu- 





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YELLOW STRIPE OF SUGAR-CANE. 15 
llas, a point between San Francisco de Macoris and La Vega on the 
railroad, the cane was normal. 

‘‘Small plantings in the vicinity of La Vega were on the other 
hand typically diseased. No cane was seen in the Santiago section 
It was not found feasible to visit the cane growing districts around 
Puerto Plata. 

“Tn the neighborhood of Monte Cristi several small plots of cane 
were found, as well as one field of considerable size, which furnished 
cane for a small sugar and molasses mill. The cane in the latter 
field was heavily infected, as high as twenty per cent of the stools 
showing the typical markings on the leaves. As in the other instances 
no stalk cankers were seen or evidence of appreciable stunting of 
affected stools. Other cane plantings in this section were also af- 
fected, the seed having been brought in large part from the above 
mentioned field. One small patch was over fifty per cent infected. 
The cane was a mixture of the Rayada or striped and a white type, 
probably the Otaheite or Bourbon. 

‘‘These two varieties were also seen in the small plots examined 
in the Republic of Haiti between Dajabén, Santo Domingo, and 
Cap Haitian. They were, however, free of the mottling in so far 
as noted. 

‘‘On the return trip to the capital very characteristic examples 
of the disease were found in small patches of cane around dwellings 
at Bonao and along the trail in and out of the same pueblo. 

‘‘With the exception of the fields at La Romana no extensive 
plantings were seen on the trip until the capital was reached. East 
of Santo Domingo City there are two centrals, each with a large 
acreage of cane. Examinations were made here and the disease 
found in abundance and very typical in appearance. Small plots 
of cane to the westward of the city along the San Crist6ébal road 
were unaffected. 

‘‘Tt thus appears that the mottling disease is widespread in 
Santo Domingo, occurring not only in the large commercial holdings 
but to a large extent throughout small scattered native patches. It 
seems reasonably certain that the disease has been present for many 
years, although there may have been recent reintroductions through 
some of the southern ports. The most interesting feature observed 
is the fact that while the leaf form of the disease—that is to say, 
the mottling—oceurs very characteristically, it was not possible to 
find a single specimen showing the cankering and drying of the 
stalks. 

‘‘One can but conjecture as to the why of this state of affairs, 

















16 JOURNAL OF THE DEPARTMENT OF AGRICULTURE. 





possibly the cane through generations of contact with the disease 
has reached a certain stage of immunity or Porto Rico has fallen 
heir to a more virulent strain. A more probable explanation lies 
in the practically virgin soils of Santo Domingo which tend to pro- 
duce vigorous, more resistant canes. It is at least clear that Porto 
Rico need have no fear of further cane introductions from the neigh- 
boring island and on the other hand it may be found advisable to 
bring over the apparently resistant canes for further trial here. 

‘“As far as the cane growers of Santo Domingo are concerned 
it does not at present appear that they need fear the mottling, but 
it would be well for them to become familiar with the disease and 
its latent possibilities for serious damage. Seed selection should be 
vigorously carried out to reduce the mottling to a minimum and 
any variety showing great susceptibility should be discarded.’’ 

One area of infection has been found on the Island of St. Croix, 
American Virgin Islands, by Dr. Longfield Smith, director of the 
experiment station. This case was very definitely known to be due 
to infected seed imported from Porto Rico. Prompt measures were 
taken to eradicate all diseased cane and it is hoped that there will 
be no spread of infection. 

Correspondence! has failed to elicit further definite information 
as to occurrence. It seems probable at this writing that the disease 
is not present in any of the British West Indies, but that it is present 
in Cuba in much the same manner as it is in Santo Domingo. The 
relation of mottling with the yellow stripe disease of Java and Ifa- 
waii, and the distribution of the latter is discussed elsewhere in this 
paper. 

VARIETIES ATTACKED.! 


The list of varieties attacked is nearly as long as that of the 
varieties known to the Island. When the first investigations of 
mottling were made one variety was found subject to attack almost 
to the exclusion of all others. This was the common white cane 
(Otaheite or Bourbon) locally known as Blanca. It was this faet 
in large part which led to the conclusions given (26) in the first 
report on the situation. Very soon, however, the striped or Rayada 


1Since the above was written information has been received from Mr. George L. Faw- 
cett, plant pathologist of the Estacién Experimental Agricola, Tucuman, Argentine, to the 


effect that a disease oceurs in the cane of that country which he believes to be similar to 
the mottling. From specimens and a photograph sent by him to the writer it has been 
possible to confirm his diagnosis. According to Mr. Fawcett the Argentine disease was 


formerly very prevalent on much grown varieties which have been replaced by others which 
are resistant to it, hence the disease is not causing appreciable loss at present. It is alto- 
gether probable that the importation of one or more of the varieties grown there will solve 
the problem for Porto Rico. 

1See Bulletin 19—Insular Experiment Station (May 1919) “The Resistance of Cane 
Varieties to Yellow Stripe or the Mosaic Disease.’’—by F. S. Earle.—Ep1ror. 





_ = lr 











YELLOW STRIPE OF SUGAR-CANE. 17 


fell prey and by the second season was no more resistant than the 
Blanca and has continued so since that time. 

A third type grown at that time in the Arecibo district was a 
dark red hard variety, the so-called Rayada morada or Sarangola, 
which was introduced several decades ago to replace less resistant 
types during an epidemic or disease or insect visitation. During 
the first season it was markedly resistant, not a single authentic 
case of disease having been found upon it. Since then it has sue- 
cumbed and while not so severely affected as the white and other 
varieties, the fact that it is susceptible combined with its poor milling 
qualities, make it an undesirable cane, and its use is no longer 
recommended. 

A variety known as Penang grown to a limited extent in the 
vicinity of Aguadilla and said to have been introduced at the same 
time as the Sarangola has been practically exterminated, and may 
well have been the means of introducing the disease to the Island, 
since it is thought to have come from the eastern tropics. There is, 
however, no direct evidence to support this hypothesis. Further 
mention of the Penang is made under the discussion of an experi- 
ment in the rate and manner of spread of the disease. 

Crystallina is the most extensively grown cane in the south and 
eastern sections of the Island, so that it is only recently that its 
resistance to the disease has come to a test. Unfortunately, because 
of its excellence as a commercial variety, it appears only too certain 
that it will prove no better than the other standard varieties. Seed 
of this variety was brought into the Arecibo region at considerable 
expense from what was at the time a disease-free area and planted 
in comparison with the Rayada. The plant crop (1919 season) ex- 
hibited enough mottled stools to make it evident that little hope 
could be had of its proving strongly resistant. As was noted this 
variety has been found infected in Santo Domingo and _ such is 
also the case to a very large extent in the newly infected areas of 
the south coast. Seed of this variety brought from Santo Domingo 
and planted near Rio Piedras produced approximately ten per cent 
of mottled shoots upon germination. 

Of the many foreign seedling varieties (for the most part those 
of Barbados and Demerara) experimented with by the division of 
agronomy of this station, all have shown infection but to a varying 
degree. Certain ones, as might be expected, have proven most sus- 
ceptible in all localities, others appear to be fairly resistant as yet, 
while others vary considerably from one locality to another in their 
reaction to infection. 














JOURNAL OF THE DEPARTMENT OF AGRICULTURE. 


B-3922 upon which extensive observations have been made, has 
been most severely attacked in all places where tried. This has 
been the case not only on the well watered north coast soils, but 
under the drier south coast conditions as well. Further notes on 
this variety are given under another heading. 

Yellow Caledonia has shown considerable variation in its sus- 
ceptibility, certain fields very severely attacked having been seen 
and in contrast others nearly free have been inspected. This state 
of affairs, however is possibly to be explained by the presence or 
absence of the disease in the locality where the cane was under trial. 

B-208 has with the exception of the Blanca suffered most severely 
of any of the kinds under observation, and it has been noted in 
this condition at Camuy, Aguada, Arecibo, and Rio Piedras. B-3412 
has likewise proven very susceptible when tried in the disease areas. 
D-117 has stood up as well as any of the better known seedlings, 
although cases have been reported where it had been nearly one 
hundred per cent diseased. 

Other varieties found infected in varying degree have been 
B-109, B-4596 (very slight), B-3405, Sealey Seedling, B-—6292, 
B-376, B-1809, D-109, B-6450, B-347, Egyptian 6VI6, 7VII7, and 
Javan seedlings Nos. 228, 234, and 856. A number of other Javan 
seedlings are known to be infected, but the numbers are not at hand. 
As far as known none of these canes as far as tried in Porto Rico 
have proven immune or even satisfactorily resistant. 

Work with native seedlings, carried on by the two experiment 
stations and two of the larger sugar companies, has hardly progressed 
far enough to give any conclusive tests. All of the Mayagiiez Federal 


Station seedlings seen (numbers one to five, were badly diseased 
wherever planted. Of the Guanica: seedlings several have been seen 
diseased and a number of others are reported to be susceptible. From 
this same source there is also the report of seedlings, only a few 
months from seed (true seed, not seed pieces), showing typical 
symptoms. 

Seedling work has been carried on most extensively at the Rio 
Piedras station, the first plants having been started in 1912. Of 
the 1912 seedlings, which were the only ones ready for plantation 
tests, a number were sent to Arecibo and Aguadilla for trial. Prae- 
tically all of these have shown slight infection as noted in the tables 
to follow. Some of them have also contracted the disease recently 
at Rio Piedras. 

Tyo additional varieties may be mentioned as being susceptible, 
the bamboo or Bambi a cane grown to some extent in the Arecibo 








Vi 


ra 





R 


—“— & @ 











YELLOW STRIPE OF SUGAR-CANE. 19 


valley, which has followed the white (Blanca) in its lack of resist- 
ance and the Cavengerie, a dark red or wine colored cane, which 
ranks about with the Rayada in its behavior. 

Variety tests were inaugurated by the station at a number of 
points in the disease-infected area in the hope of finding one or 
more types that would give satisfactory results in the presence of 
the disease. The results of these from the standpoint of tonnage 
and other agronomic factors have been reported by the plant breeder 
(8). Notes were taken on the percentage of diseased shoots showing 
in the various test plots as a measure of the susceptibility of the 
varieties involved. In some cases only one count was found pos- 
sible during the season, but the data, though very incomplete, is 
given for what it may reveal concerning varietal resistance. In all 
of these experiments selected seed of the various varieties was sent 
out from disease-free plots at the experiment station. For the check 
plots the Rayada or striped variety was used, seed being obtained 
locally in each case. Most of it came from fields showing varying 
amounts of mottling but an effort was made to have healthy canes 
only cut for the purposes of the several experiments. 

In the first experiment conducted near Aguada one-twentieth- 
acre plots were used the seedling types being alternated with the 
native Rayada. Only one count was made at the time the cane was 
about a foot high. The figures following indicate the number of 
mottled stools counted. Poor germination in half of the field will 
account for the small numbers in the latter portion of the table. 
Most of the varieties used were planted in triplicate. 


Rayada ~-_--- 29 Rayada __--- 12 Rayada ___-.. 2 
B-1909 _-_-_ 20 B-1809_..-. 3 B-1809 _____ 7 
Rayada —.--- 20 Rayada —--~-~ 14 Rayada ___-- 9 
B-376 --..-- 26 B-376__--_. 9 ee 4 
Rayada _---- 19 Rayada ~_--- 19 Rayada _---_ 4 
B-6292 _-—_- 13 B-6292 ----_ 11 B-6292 _____ 6 
Rayada ----- 20 Rayada_.--. 9 Rayada __-_~ 2 
S. Seed.t__-_ 38 S. Seed... 9 S. Seed... 7 
Rayada __--- 32 Rayada ~---- 10 Rayada __-_- 16 
B-3405 _---- 6 B-3405 _..-- 3 B+3405 _____ 6 
Rayada ----- 19 Rayada —_-~- 2 Rayada ~--__ 16 
B-6450 ----- 7 B-6450 —-__- 6 B-6450 _--__ 1 
Rayada __--- 19 Rayada —~.-.- 5 Rayada ~---. 8 
<< 18 i oe 7 D-117 ____-- 7 
Rayada —--_-- 17 Rayada __--- 4 Rayada __-__ 9 
h-it...... 0 D100... 5 ae) ee 1 


1 Sealey Seedling. 














JOURNAL OF THE DEPARTMENT OF AGRICULTURE. 


20 

















normal at the right, mottled at the left. 


FIG. 3.—Leaf sections; 











Q 


Bases de Hojas Enfermas 


Variedad Cristalina 


Bases of Diseased Leaves. 


Variety Crystalline 





1 














YELLOW STRIPE OF SUGAR-CANE. 


Rayada ____-_ 9 Rayada ____- 12 P, R.-292___- 

P. R.-208_--__ 2 P. R.-260_-_. 1 Rayada_ .-. 5 
Rayada —_-_-_ 3 Rayada _____ 12 ¥. Caled? .... 2 
P. R.-210_--_ 4 P.R-272__.. 2 


These figures give some indication of the relative behavior of 
the various varieties employed with respect to mottling since all 
were equally exposed to infection from the surrounding badly dis- 
eased fields. It would of course require further counts through the 
season and especially of the ratoons to be at all certain of the results. 

Another plot in the same neighborhood planted the year before 
as a fertilizer experiment was also examined with the following 
results. These were tenth-acre plots. 


Ste 8 oo 91 mottled stools. 
D-109_______ ee eee __.... 20 mottled stools. 
B-3412__--__--____-_-___._. 99 mottled stools. 
Ns et re le ee -- 117 mottled stools. 
B-4506... 2... eee eee ee 7 mottled stools. (4 doubtful). 
ROO 2 ook Sen ee ee -- 58 mottled stools. 
BAVAC AE 22352 ee 112 mattled stools. 


This more nearly indicates the comparative resistance of certain 
well-known varieties. Two which have been considered very valu- 
able kinds and recommended for large scale planting here prove to 
be most susceptible, equalling or surpassing the Rayada used in 
check plots. These figures represent fifty to sixty per cent infec- 
tions. The most promising canes were D-109 and B-4596 which 
have also given promise in other tests. It is of interest to note that 
B-4596 is a variety eliminated from the experiment station tests 
several years ago because of its great susceptibility to Cytospora 
sacchari, an imported disease which causes a stalk rot. This disease 
Was not present on the cane in the experiment under discussion. 

Near Vega Alta a variety experiment was gone over once early 
in the season with the following notes resulting. As usual, sur- 
rounding fields were diseased, in this instance between two and three 
per cent. 


Reyada:.....---<=- 9 avai 222 7 
B-3406:.. == 3 Yellow Caledonia -- 0 
eG 568 os 3 Be4596 2.2. - =. 3 
Kayade.........--- 19 Rayada.....~..=..- 11 
'B-6460 .=.=5-....-. 1 3: |: ae 5 
Crystallina ..._...- 5 


An extensive test of varieties was put in in the Arecibo valley 


2 Yellow Caledonia. 





20 JOURNAL OF THE DEPARTMENT OF AGRICULTURE. 


again employing selected Rayada for the checks, the seed being 
secured from adjoining fields. Two counts at several months in- 
terval were possible here. The figures given indicate the number 
of stools showing one or more mottled stalks. The plots in this ex- 
periment averaged two hundred and ten stools each so that some 
idea may be gained of the rapidity with which the disease can infect 
from adjoining fields. 





Variety | First — Second Variety | First — Second 
examination | examination | examination examination 






LOW FN NOW RE IUION RON OTNI® 





Cf oe | 5 4 || Rayada......... 16 18 
ee | 0 | 0 || D-117.. 7 12 
Rayada.. 3 8 || D-109,,,. 2 3 
LT eee 0 1 | Kayada 27 29 
S. Seed !., 0 2 || B-1809. § 7 
Rayada .. 2 12 || B-376....... 2 5 
MES 6 ovnececce 9 6 || Rayada ........ 19 24 
_ oy eee 2 BOS. os se vec 4 
Rayada ......... 16 24 | S. Seed ',....... 1 
| 0 1 || Rayada ........ 3 
> eis 1 it. . ———— 2 
MOVOGR .....s05s 12 21 |] B-4006 .....cccce 2 
| Saas 3 | 3 || Rayada........ 10 1 
eae 3 gl eae 1 
Rayada ......... 14 83 || B-6450........... | 0 
| eas 3 3 || Ravyada .| 3 
B-1596 ........... 0 | 2 || D-117....... 26 0 
Rayada ......... 1 9 || P. R. 208 cal 1 
ae 8 8 | Rayada ie 1 
ah, | ere 5 7 || P.R. 210 vat 1 
Ravada ......... 7 13 || PR. 260 be 1 
J eee 12 13 || Rayada ol 10 1 
eee 11 15 || P. R 272 ¥ 4 
MINER sece sees 6 8 || P. R. 292 e 2 
ae 6 13 | Rayada a 3 
eae 0 | 3) P.R. 317 “t 0 
Aun Gen En ebb MENGE UTI dnd ank cudcwien baadeesasedeaeree | PR. 318 0 





1 Sealey Seedling. 

NoTE.—Several cases in which there was a reduccién in number on the second count 
are due to the dying of the stools or shoots from diseased seed pieces in the interim. 

B-4596 again gives considerable promise of being satisfactorily 
resistant as do several of the Porto Rico seedlings. 


SYMPTOMS.? 


The one marked and constant symptom of this disease, and the 
one by which it is easily recognized by any one who has occasion to 
visit diseased fields is the peculiar mottling of the leaves. It is 
readily distinguishable from any spotting or striping or other abnor- 
mality of cane leaves known to the writer. No trouble has ever 
been had in. definitely ascertaining whether or not the disease was 
present except in a very few cases, where in new areas or new fields 
a part of a leaf or a few leaves only were found abnormal. A de- 
tailed comparison of the symptoms of mottling with those of other 
diseases with which it might be confused, is given further on. 


1 Adapted in large part from the 1916-17 report. 








} 


_— 
coro CO 


‘~ t 
faaws 


mem Onmoctinec 


— a oo ate 6 











YELLOW STRIPE OF SUGAR-CANE. - 23 


In fully expanded mottled leaves of the type commonly found, 
the backgrounds are green to yellow-green, depending upon the se- 
verity of the case. Two rather distinct types of discoloration have 
been noted but always grading into one another so that it is not 
considered that they are other than phases of the same phenomenon. 
Of these one is more common in early stages or light cases and has 
been especially noted in the unfolding leaves at the top of a stalk, 
sometimes changing to the second after a time. In this type the 
background or larger portion of the leaf-blade is a light, abnormal 
yellow-green and scattered about in it are areas of apparently normal 
color, ‘‘green islands,’’ as it were. These spots are for the most 
part linear, but will vary from mere points to irregular blotches 
several centimeters long by a centimeter wide, always with a deeided 
tendency to greater length than breadth. This phase is much more 
apt to be confused with certain other phenomena than the second, 
especially where the disease is making its first appearance in a new 
area. 

The most usual phase of this disease seen, the one occurring 
over thousands of acres and in all varieties) is that in which the 
leaves are marked with numerous very light yellow-green to nearly 
white spots and short stripes. The background will vary in color 
from a normal green in plants but recently attacked to a yellow- 
green in more severe cases. The markings which produce the mottled 
effect are always much lighter in color, giving a very decided con- 
trast. They are irregular in shape varying from almost invisible 
points to irregular spots two centimeters in their greatest dimension. 
For the most part they are linear, coalescing irregularly, and with 
indefinite margins. They will at times constitute fifty to sixty per 
cent or more of the total leaf surface. 

The mid-rib remains to all external appearances normal. The 
leaf-sheaths present no abnormal signs, except a faint mottling in 
early stages of growth. 

Mottled leaves do not die and fall away from the stalk any sooner 
than do normal ones, nor on the other hand is there any tendency 
to remain past the usual period of shedding. Varietal characteristics 
hold in this particular, irrespective of the presence or absence of 
mottling. There is no difference in the size of the leaves until the 
general stunting of the stools sets in in advance stages. 

As a general rule the leaves are uniformly mottled, but in begin- 
ning cases examples are not uncommon in which a portion of a leaf 
only is affected. Such instances have been found where a stalk pre- 
viously apparently normal commences to show mottling. The lower 











24 JOURNAL OF THE DEPARTMENT OF AGRICULTURE. 


leaves, anywhere from two to a dozen in number, will be to every 
appearance normal, then there will occur a leaf showing mottling for 
a faw inches only at the base of the blade, which in turn will be 
succeeded by several others above affected from a half to two-thirds 
their length. All above these transtional leaves will be completely 
mottled. Occasionally one half of a leaf may be affected further 
than the other. The reverse condition of normal appearing leaves 
above mottled ones has not been observed. Through the season there 
may be in this manner a gradual increase in the number of. stalks 
infected or at least in the number showing visible signs. 


The disease follows what is approximately a three year course.! 
In the first year of its presence isolated stools only will show dis- 
coloration, scattered irregularly over the field and often composing 
less than one per cent of the total. One to five per cent infected is 
the common condition found in what is considered the first stage. 
At this time the only svmptoms will be the mottling of the leaves 
above described. Often the first phase only will be present, or where 
the second also oceurs the background will still be dark green. In 
a given stool the number of stalks showing mottling may vary from 
one to all, two or three, however, being a very common number. This 
in many cases merely means that the shoots from one seed piece only 
are infected (a number of seed pieces, usually four, are planted in 
each hole and the shoots from these form the stool). It is easy 
enough, however, to find shoots from a single seed-piece only part 
of which are mottled. 

At this point in the progress of the disease since no other symp- 
toms than the mottling will be found externally or internally, it is 
impossible after the leaves are removed to distinguish normal from 
abnormal cane. The internodes are sometimes somewhat shrunken, 
but the only sure test is to plant portions of suspected stalks and 
observe the leaves of the new shoots. 

In the second year at the usual rate of procedure a very much 
larger percentage of infection is present. As far as it has been pos- 
sible to ascertain, this includes all stools which showed mottling the 
year before, as well as a varying number of those‘ that had been, 
when the first crop was cut, apparently normal. At this stage, in 
addition to the mottling, there may be a dwarfing of the stools and 
the canker stage may be present, depending somewhat upon the va- 
riety and possibly other conditions. The dwarfing may be sufficient 
to cause a loss in yield of from ten to sixty per cent. There is quite 


EDITOR. 





1 Other observers do not entertain this opinion as to a three year course. 

















YELLOW STRIPE OF SUGAR-CANE. “ 925 
a decided shrinking of the internodes whether the stools are stunted 
or not. 

The crop in the third year (second ratoon) is practically a total 
loss at the usual rate of progress... This is due to the combined 
effect of dwarfed stools producing very short lengths of merchant- 
able cane and the dry pithy nature of the stalks themselves, due 
to cankers, cracks, and lack of juice. 

There have, of course, been considerable variations from this 
three-year sequence, depending upon varieties and other cireum- 
stances, but it holds to a very large extent. 

A second very marked sign is what has commonly been referred 
to as the canker stage. This occurs more severely on certain varie- 
ties than on others, and similarly appears on certain ones before it 
does on others in point of time. The soft white canes, the Otaheite 
and Bamboo for instance, are peculiarly subject to it, fields of these 
varieties often entering this stage in the second year. The Rayada 
and other hardier canes show less of this phase of the disease as a 
rule, but fields do occur in abundance where these canes are seriously 
cankered and rendered absolutely worthless. 

The cankering is plainly an advanced symptom, since a_ stool 
may show mottling through two seasons before it appears, and in 
one variety (Sarangola) only a very little has been noted as yet. 
The stem lesions or cankers originate and can be found on the inter- 
nodes before the leaf-sheaths have loosened. At this period the 
lesions are first noted, as somewhat shrunken areas with a water- 
soaked appearance, soon becoming medium brown in color, and oval 
to linear, often irregular, in shape. With the falling of the leaf 
they pass through various shades of brown and finally to an ashen 
or dull gray color being still sunken, linear, and often coalescing to 
form large irregular areas more or less completely covering the en- 
tire internode. On the other hand, they may be limited to a few 
only on each internode. The margins of the lesions are quite dis- 
tinct. They do not pass from one internode to another, the nodal 
regions forming a sharp line of demarcation. 

Penetration of the tissues is never very deep, hardly more than 
from one to two milimeters at best, and is often limited to a few 
layers of cells only. The affected tissues are red but not different 
in shade or other characteristics from similar effects produced by 
other causes. There are no other internal symptoms except as noted 
below. 


1Mr. Childs, manager of Central Los Cafios, has data that show that five-year ratoons 
that had been infected for several years have produced as high as 25 tons per acre.—EDITOR. 











26 JOURNAL OF THE DEPARTMENT OF AGRICULTURE. 

















FIG. 4.—Cane stalks; normal in the center, cankered at the sides. 

















YELLOW STRIPE OF SUGAR-CANE. - a 

Cracking very often accompanies the cankering, and along these 
openings the same reddening of the tissues occurs, but it is of the 
same nature and extent as occurs in splitting of normal cane. Crack- 
ing is by no means an uncommon phenomenon; some varieties, and 
especially large stalks, being very subject to it. For this reason 
no special significance is attached to it as it occurs in connection 
with the cankers, other than to consider it a result of drying of the 
stalks, quite to be expected. 

In addition to the stunting or dwarfing of the stools, there is a 
shrinking of the internodes of the individual stalks. This is es- 
pecially pronounced in what might be termed third phase cases, or 
those in the last stages of the disease. Such stalks are almost com- 
pletely lacking in juice, the limited amount of pith tissue formed 
being of a rubbery consistency. Where the trouble is not so far 
advanced the lesions may be present to a greater or less extent 
without an appreciable shrinkage of the internodes. 

One peculiar circumstance that has been often noted in fields 
in approximately the second phase of the disease has been the finding 
of stalks showing only part of the internodes cankered. For instance, 
the lower five or six would be apparently normal and all above 
cankered and shrunken, or the lower internodes normal with five 
or six above cankered, and the balance above again apparently 
healthy. As an extreme case there may be noted a stalk of Rayada 
found above Arecibo, the condition of the internodes of which, pro- 
ceeding from bottom to top, was recorded as follows: Four normal, 
five shrunken and cankered, four normal, five shrunken and can- 
kered, top joints to all appearances normal. This sequence is un- 
doubtedly due to an alteration of wet and dry periods. 

In every case examined canes showing cankers, even if of one 
internode only, have also been found to have all the leaves mottled. 
On the contrary it has been very common to observe field after 
field showing mottled leaves in abundance but with no stalk cankers 
present. 

There have been reports of apparent recovery from the mottling 
condition, but it has not been possible to investigate any such cases 
and they are considered very doubtful at best. 

A rotting of the bud is never a sign of this disease and such 
limited cases as do occur can always be attributed to Diatraea or 
other agencies independent of mottling. 

Nothing abnormal has been found in so far as the roots are con- 
cerned. As would be expected with cane growing under the condi- 
tions which have prevailed in the infected territory, there can always 














98 JOURNAL OF THE DEPARTMENT OF AGRICULTURE. 
be found great numbers of dead roots, but no more than in normal 
cane growing in the same region. The presence of one or more 
root fungi, of course, often complicated diagnosis, a point discussed 
under another heading. 

Cuttings of normal and mottled cane (B-3922) taken from the 
same relative parts of the stalks and as nearly equal in size and age 
as possible were placed in standard nutrient solution. Wateh was 
kept on root development over a period of several weeks or until 
the cultures were overgrown by molds. At no time was there any 
observable difference between the two lots. 

A series of these cane cuttings were planted in the green house 
and one of each (normal and diseased) dug up carefully at intervals 
of a week, beginning as soon as the first shoots broke through the 
soil. As in the preceding experiment it was not possible to find 
any differences worthy of note. 

It is not believed that there is any noticeable loss in germinating 
power of seed from affected stalks except those in advanced stages. 
Nothing of this nature has been noted in the planting tests nor has 
it been reported or observed in the field, although very little seed 
visibly infected has been planted, at least in the last year or two. 

The symptoms of the mottling disease in brief may be said to 
be a mottling of the leaves, with no other observable change in the 
plant at first followed, generally in the first or second ratoons, by 
a dwarfing of the plant, the presence of cankers or lesions on the 
stalks, and a decrease in the amount of juice. 


OTHER HOSTS. 


Constant search has been made for other host pests since the 
finding of any such might well shed light on the origin of the disease, 
or make possible the obtaining of other valuable data. Grasses grow- 
ing in and about cane fields have been particularly watched with 
this object in view. A number of specimens, for the most part malo- 
jillo (Panicum barbinode, Para grass), were found or sent in by cor- 
respondents showing varying amounts of chlorosis. These plants 
were set out in the plant house and grown for observation. The 
resulting new growth in all cases was entirely normal indicating that 
the clorotic condition observed in the field was physiological in 
nature. 

Lyon! states that corn (Zea mays) is very subject to an infec- 
tious chlorosis in Hawaii, closely resembling if not identical with 
what he designates as ‘‘yellow striping’’ of cane. This condition has 


1 Unpublished note. 

















YELLOW STRIPE OF SUGAR-CANE. 29 
not been noted as yet in Porto Rico. Longitudinal white stripes 
of varying width are common on the leaves of the corn here, as well 
as on certain cane varieties as noted hereafter. They are doubtless 
of the nature of color chimeras and are therefore of more interest 
to the plant breeder than the plant pathologist. 

The search for other host plants should be continued in order 
to thoroughly examine into the possibility of the theory advanced 
by some that the disease has originated on wild grasses in the up- 
land districts and spread from these to the cane. 


RELATION OF ENVIRONMENTAL AND CULTURAL FACTORS. 


The field survey. 

With the aim of inquiring into all possible conditions which might 
influence the disease directly or indirectly, or even be of a causal 
nature, various environmental and cultural factors have been studied 
both in field trips and in plant house experiments. 

Throughout the course of the studies a large number of field 
trips to all parts of the Island and of course to affected districts in 
particular were made. In addition to those made by the writer, 
assistants in the division of plant pathology have also aided in this 
phase of the work, and results here recorded include information 
hased on their reports as well as upon information obtained by cor- 
respondence and conversations with other members of the station 
staff, cane growers, and others interested. 

[t was realized, however, that while many facts were being ob- 
tained in this way, it was desirable to have data in greater detail, 
and in more orderly arrangement than the above methods permitted. 
Accordingly a form embodying the points upon which information was 
desirable was drawn up. The plan was to send out field agents to 
cover the entire Island as rapidly as possible, one of the forms being 
filled out for each field visited. This work was well under way before 
the writer left the Island and had advanced far enough to demon- 
strate its value. The outline used in this survey is as follows: 


FIELD SURVEY—CANE DISEASES. 


Pield Nee... ees é 
ACKOARE 2225-555 . 
Pads 2s see et es oe mee 
1, Location__---- a cs = 
2. Type of soil___--- a I a a 
2. Nature of tertain.._..........-.-.--.-===--+-=-4-4+.4=-=-____ === 
> Wanlety.-2-22522— a a a meee 














30 JOURNAL OF THE DEPARTMENT OF AGRICULTURE. 


6. History of the field: 


(e) Plant_..~-- aL ae nee eee ee SALOON oa os ae oa 
(b) Previous crops__------ ics ee eee ee ee 
(Oo) oars in canes = (d)) Septemen: = a= oe oa 


(If more than one variety present, give percentages for each.) 
(a) Percentage showing cankered stalks___._____-_--------~- pemieies a  e Ss 
a) Seen OIG COISGRNE SaIIEG ADDORT sss ass eso ee oeeeeoo eS. 
TOO) a | (ae a ee Did field show disease?___----__-_ 
9. Cultivation practices. 


6. Percentage of stools showing mottling_--- 


Lime 
i Ee: a ge ee ee ee pee 
Extent of plowing, harrowing. .2—. =... 2-o.65--205-5255 
Seed selection ~_-- 
Seed treatment 
Trrigation or drainage__-- 


SORBONNE URMMAUR ION 2. ooo a a am 
BRD OY MONI AUR oo ee ei eo bay Seta oe 
PPINIHAN GOT AMMEN Soe acon aek ea 


10. Other diseases present : MasteNaneonus 8 o-oon5 oot 
CU ae Be ei areata ean Belem iii et 
LE 2 ea ee Cercospora ~_-~-_-- Se eee mene 
Rind disease__----~-- stilt ate eel DARE MNGUR a 
TST EAE ee ee ee eye eee ereanesere eG AbPIpING = 38 at oe 

11. Insects: 

Diatraca......... pa oe eee ere poe eee ee NVINUES PIN ao oe 
[oT | a ae a ee Muisooueneots <2 222 oe bak. 
12, Remarks-_---- 


The aim of this outline was several fold, the data to be of use 
not only to pathological workers but to the entomologists and agron- 
omists as well. It was designed to provide in convenient form the 
character of cultural practices, the nature of the soil, the history 
of the occurrence of the disease, and any other information obtain- 
able as to presence of other diseases or injurious insects. Not only 
was it expected to prove of value in the mottling studies but to serve 
as a guide in other sugar-cane investigations. 

In the following table is given the salient features of a survey 
of a considerable portion of the sugar-growing lands of the lower 
Arecibo valley in so far as they apply to mottling in which these 
forms were used. This work was performed in the summer of 1917 


by Mr. E. D. Colén. 





a a ae ee ee 


GAR-CANE. 


1 OF SU 


E 


YELLOW STRIP 


UONBAT[ND poor 
UOTBAN[ UD poor 
uONBaN[Nd pov?) 
UONBAN [ND poor) 
UONBAN [ND poor 
UONBAL [Nd poor 
UONBAY[ND poor 
UONRA[ND poor, 
UOMBAN[UD poor 
UONBAN[ ND poor) 
UOT RAL [ND poor 
UONRAN[ND poor 
UONBAN[ND poor 
UONRBAT No poor 

UONBIS JUDUIAd X| WoL, pads 
UOT RIS JUBUTLIAad Xy WOU pa 
SOUB) SOT WOLJ pods 
UONBANTOO poop | ' 
UONBIS JUBUIIId XG WoL poas 
UONRAN ND pooy ) 
UO!]BIS JUdUTILAd XY WOT paas ) 
UONBANTND poor 
UONBAT]NO poor 
UOTIRAT[UD poor 
UONBATTND poor) 
UOMBAN[ND poor 
pordde sazynaag } 
UONBALND ABy Sf | 
UONBAN[ND poor 
UONBAN[ND poor 
SOSINOD 19}BM aSIOM 


ivou OSBASI(] 


SYIBUI Y 





6-08 


aSBASIp JO % 


9I6L pajuBjdai uooiey 
9I6L paiusldal uooiwy 
9161 po1uBidas u00 ie Yy 
UO0OTBRI ISAT 

“"gooIwl YO 
“"""""9uBo 1UBI[d 

“OuUBO TUBId 

“* yoo wl paly 


)° "moo BL YIN +4 
“*"" WOOTBRI PALL 
“*"Wo007]B1 Wun0d4 

"** TOOIBL ISAL] 
"** TOO TRA ISAT 
IUBD JUBId 
ouBd UBL 
“‘ouBo 1UB[q 


UBD JURE 
LIGI 
LIGI 


“9uBd JUBId 


U007TBI SILA 
LIGI “""guBd 1UB[ 
LI6I * 000]BI PILL, 
LI61 “** qooyel YANO 





9I6T “**" 007] B1I PALL 
ate de uo0oyes 
9161 piry) ynoqgy f 
9161 *"uoOIW ISI 
LI6I | foueo jue 

* m00OjBI puw / 


(3) FI6T +++ querd paxte ( 


porvodda 


asBasic] sdo1d JO ‘ON 


“Ajoyeutxoidde e108 [T = vpianp 


BpBABY 

*‘ epeisy 
* Bpercry 
BpBABY 

“"* BPBARY 
“"* BpBARY 
“* epBéuy 
BpRABY 
BpBAéBy 

“* BpeARy 
BepRiry 
BpBABY 

“ upRAny 
“* BpBivy 
“Bul BISAID 





ve ups Avy 
“806-4 

“BpBAByY 80c-A LIT 
“" BpBiny 

** BpBiBy 

“* BpBiRy 

“ss apedey 

“* epesry 
BpBARy 

BpBABy 

BpBABY 

“* epetey 


auBd UL 


SIBIOX AJOTIBA 


“sppsand UL VaALY 


“** ULBOT IIIS  O00F 

“* WBOT TIS | 009 
“*uBol 07 ApuBs 
UdATS JON 
uso; ApuBs 
“** (BOT ITIS 
“" UIBO] VIS 
WIBO] I[IS 
WBOT A[[AA BIA) 
“*"ureo] ABI) 
wWIBOT IIIS 
** BSOA-91GOS 
* &Byjo 0) Apurs 
WBO| Apuss 
* ULRO'T 
wot 
uLBo’} 


weo] Apuss 


“""upol Apusg 
"mp0, ApuBs 
“"urBo] Apuss 
**** UIBOT [AABIN, 
Se *@ABIT) 
— eid 
* ABIO 

“* wroy Apurg 
uvo] AABOH 


* WBO] TIS 


EBay: pid 





‘AOTIVA OQToeIy oy UT 


ASAING pPlepi JO sinsoy—' II e1qey 











32 JOURNAL OF TILE DEPARTMENT“OF AGRICULTURE. 


A study of the data here presented bears out statements to be 
enlarged upon further on that soil, variety, years in cane, and other 
cultural matters have no direct bearing on the disease. 


A similar survey was conducted in the Cayey district, an en- 
closed valley in the interior of the Island, which has been free of 
disease until comparatively recently. Some two thousand acres in 
six barrios were gone over here by Mr. Juan Simons, Deputy Agri- 
cultural Inspecter. 

A table from his field notes has not been prepared because of 
its similarity in salient features to the one already given; but his 
conclusions, adapted from his field report, are as follows: 

‘‘In all fields inspected the presence of the mottling disease of 
cane was noted. The infection varied from three to four per cent 
in the least diseased fields to sixty per cent or over in the most 
severe cases, With an average of ten to fifteen per cent. 

“It is to be especially noted that plant canes, with three or four 
exceptions in barrios Beatriz and Vegas which had an average of 
six per cent infection, were as heavily attacked as ratoon canes. 


‘*Ratoon cane with rare exceptions was generally severely at- 
tacked by this disease, having in almost all cases more than twenty 
per cent of mottled stools. In barrio Rineén for instance there was 
an area of more than two hundred and seventy-five acres of ratoons 
with an average of sixty per cent of mottled stools. Canes from 
these fields are being used for seed purposes in the new plantations 
which, of course, means the dissemination of the disease, and hence 
the high per cent of infection in plant cane. 


“The soils in this region are for the most part of heavy clay, 
but are usually well drained. The fields are mostly hilly or rolling 
although there are great extensions of plains, but in no case was 
it noticed that the disease favored any particular class of soil or 
terrain, being found in equal intensity on hills and lowlands. In 
general the mottling disease is widely spread throughout the cane 
region of Cayey.’’ 

This will suffice to give an idea of the scope and purpose of the 
field survey. Most interesting data should result from the complete 
reports. As these records are made for individual fields, the location 
and name or number of each field being recorded, it will be possible 
in selected localities to make a second survey and so obtain informa- 
tion as to the course and behavior of the disease from season to 
season. 








Cu 


at 
tis 
al 


Ca 

















YELLOW STRIPE OF SUGAR-CANE. 


Cultural factors. 

Because of the very great importance of cultural methods in 
their relation to most other cane diseases than the mottling, much 
attention has been given them throughout the course of these inves- 
tigations. The cane troubles known as root disease and deterioration 
are so prevalent on the Island, and so widespread, that too much 
cannot be said as to the value, and, in fact, the necessity, of proper 
methods of cultivation, using the word cultivation in the broad sense, 
even though as is now apparent cultural factors do not in themselves 
serve to influence mottling. 

The reiteration of these recommendations in various publications 
during the time the disease has bee: under study, as well as the 
earnest. effort of the various sugar companies and growers to do: 
everything possible to combat the mottling disease, have resulted in 
a thorough trial of all possibilities in this direction. The results. 
will be briefly summed up below. 

Deep plowing has been carried out in a number of localities both 
by means of steam plows and by tractors which are now well estab- 
lished on the Island. In some places at least, where the disease was 
present in disastrous amounts the fields been prepared for planting 
were plowed five and six times. Sufficient fields have been examined 
which had had excellent cultivation including a number of deep plow- 
ings to make it evident that such work was without any practical 
results as far as control was concerned. As much disease would be 
present, other conditions being equal, as where shallow holes only 
were made by hoes and no subsequent cultivation given. There 
would, of course, be an increased yield and relative freedom from 


other diseases. 


Effect of fertilizers. 

Great attention has been paid to the matter of fertilizers. Of 
recent years it had been found profitable on practically all the cane 
lands of the Island to apply chemical fertilizers. With the break- 
ing out of the European war the supply was interfered with, cer- 
tain ingredients becoming unobtainable, and even those available 
were very high priced. Many growers were inclined to place the 
blame for the poor condition of the cane on the lack of fertilizer, 
and they were doubtless correct in so far.as yield and other factors, 
with the exception of mottling, were concerned. 

The Insular Experiment Station has conducted over several years 
a number of very careful fertilizer experiments in various parts of 
the Island, and more especially in the western portions. Results. 





34 JOURNAL OF THE DEPARTMEN'T..OF AGRICULTURE. 


of these all appear in the annual reports of the station, and while 
they show clearly the value of fertilizers, often resulting in as high 
as fifty per cent gain in yields, there has never been the slightest 
evidence that there was any effect in controlling, or even in checking, 
mottling. This has been borne out by fertilizer experiments con- 
ducted by some of the sugar companies themselves. The following 
paragraph taken from a report prepared by Mr. Bourne in charge 
of experimental work for the South Porto Rico Sugar Company is 
representative of these tests. 

‘‘Tablon 7, in addition to its thorough tilling had a fairly good 
dressing of cow peas. In December 1917, sulphate of ammonia was 
applied at the rate of 300 pounds per acre to the 7.5 acres of B-3922 
in Tablén 7. This part of the field was most affected and the sul- 
phate of ammonia was applied to see if it would help to throw off 
the disease or turn the foliage greener. No change for the better, 
however, could be seen except that it caused a slight stimulation 
in its general growth. 

‘*About the same time an experiment was conducted in triplicate 
plots in Tablon 9 with sulphate of ammonia, lime and filter press 
sake (cachaza). The sulphate of ammonia was applied at the rate 
of 540 pounds per acre, lime at the rate of two tons per acre, and 
the cachaza at the rate of thirty and sixty tons per acre. Check 
plots were left without any treatment, and up to the present there 
is no noticeable difference in any of the treated plots to those not 
treated.”’ 

To test the matter under more nearly controlled conditions an 
experiment was laid out in the plant house. Two-eyed cuttings of 
the variety B-3922 as nearly comparable as possible were used, ten 
each of normal and diseased being planted, and each in a separate 
container. After germination fertilizer of a standard 12-6 formula 
(twelve units of nitrogen and six of phosphate, potash not being 
obtainable nor for that matter necessary) was applied as follows: 
Four ounces to each of four cans, two ounces to each of four cans, 
leaving two without any applications as checks. Two to four ounces 
is the usual amount applied per stool in field practice. No effects 
were seen at any time, other than the slightly better growth of 
normal cane. 

Claims were made that sodium nitrate would ‘‘cure’’ the dis- 
ease and experiments were in order to prove or disprove this claim. 
Again using potted cane in the plant house, two ounces of sodium 
nitrate were applied to each of four cans, and four ounces to each 
of four, leaving two cans in the row of ten as checks. At the time 














— SS ee 


wt 


\u 











YELLOW STRIPE OF SUGAR-CANE, 385 
of application the canes in all ten cans had reached a height of about 
two feet and all were typically mottled. The four-ounce application 
was sufficiently strong to cause the death of the plants to which it 
was applied. In the case of the two-ounce doses there was a deep- 
ening of the green color of the leaves which somewhat obscured the 
mottling, but otherwise there was. no change, and certainly no cure 
in any sense of the word. It was doubtless this effect, seen without 
careful examination, that led to the statement made. Where the 
cane had been killed, replantings of diseased two-eyed seed pieces 
of B-3922 were made. These suffered the same fate ultimately as 
their predecessors, showing mottling, however, as long as they were 
alive. Field tests in various localities have given the same results. 


Liming. 

Great hopes were at one time entertained as to benefits to be had 
from liming. As with other possibilities trials were made under 
varying conditions but with negative results as far as mottling was 
concerned. In following out this proposition several limed fields in 
the western section of the Island were very carefully gone over. 
Moreover a plant house experiment was set up and only served to 
make the negative results more evident. In this experiment cuttings 
of the same kind as used in other plant house tests were employed. 
Ten pots of mottled cane were assigned to this test, two serving as 
checks, two with a half ounce of air-slacked lime, four with one 
ounce, and two with two ounces. Lime is of value only in so far 
as it increases yields. 

Ground or powdered limestone has been reported as a certain 
cure and is said to have been tried out by a number of growers but 
there does not seem to be any general movement to apply this ma- 
terial. The writer has not been able to locate any fields where it 
had been applied successfully. As a fertilizing agent it would be 
of somewhat less value than slacked lime because of its limited 
availability. 


Seed treatment. 

Seed treatment at the time of planting has been advocated as 
a preventive measure for the pineapple disease or black rot (7'hiela- 
viopsis paradoxa) and has been generally adopted for this purpose. 
In all publications on the subject it has been clearly stated that the 
dipping or soaking of cane seed in Bordeaux mixture was not effec- 
tive for the control of any other disease than the pineapple disease. 
In spite of this warning, however, Bordeaux treatment has been re- 
peatedly tried in the hope of checking the mottling, and of course 








35 JOURNAL OF THE DEPARTMENT _OF AGRICULTURE, 


with absolutely negative results. At no time after the infectious 
nature of the disease became apparent was dipping recommended. 

No direct experiments were performed, the experiences of the 
growers being sufficient, but it may be noted that of several hundred 
diseased cuttings planted in the green house experiments all were 
soaked in strong Bordeaux mixture for at least fifteen minutes and 
without exception all produced mottling shoots. 


Ratooning. 

In comparison with Santo Domingo and Cuba very limited ratoon 
crops are possible in Porto Rico, and in fact in large portions of 
the south coast it is the custom to replant every year. As a general 
rule not over two ratoon crops are obtained although there are excep- 
tional cases where as high as fifteen or twenty crops have been ob- 
tained. In such cases, however, much replanting is necessary every 
vear. In a disease of the nature of mottling there is an accumulative 
effect which, as has already been pointed out, proves disastrous in 
the third year or second ratoon in the usual course of events in 
Porto Rico. Where the disease has gained considerable headway in 
a given field no further attempt should be made to obtain a ratoon 
crop but the whele should be plowed up as soon as possible after 
cutting. 

Drainage and irrigation. 

These two points while of the very greatest importance in any 
consideration of root disease, deterioration, or similar cane troubles, 
do not seem to have the slightest connection with mottling. The 
results of field observations combined with the data of the field sur 
vey fail to indicate any such relation. All types of fields are invaded 
alike, 

Disposition of trash. 

This phase of field practice, discussed at some length in an earlier 
report. (26) is now seen to have little effect on the mottling. The 
stand taken in that report is not receded from in so far as it applies 
to cane growing independent of the disease. Burning of the trash is 
2x most objectionable practice and every effort should be made to 
conserve it for the benefits to be derived fresa its presence on the 
land. There will be an indirect benefit, even i the disease situation, 
since proper handling of the trash makes for increased yield which 
will serve to counterbalance in soime measure losses from the disease. 
As far as the results of the field survey have been examined there 
is no evidence that burning or non-burning of trash has had any 


direct influence on the disease. 














MoTzeIg JWourtrodxg eMsuy ‘MeTA epts-yyou ‘esnoyweld—“s ‘OI 


___ ss Lid 


AR-CANE. 


=) 
1 


OF SUC 


9 
“ 


& 
A 
—_ 
i 
cc 
| 
= 
RN 
» 
= 
- 
oe) 
5 
| 
~ 
a 























88 JOURNAL OF THE DEPARTMEN¥ OF AGRICULTURE. 


Effect of soils. 

As with the preceding topics negative results only can be re- 
ported concerning the relation of different soil types. This was a 
point given consideration in the field survey and, as noted in the 
discussion under that heading, it was impossible to detect any effect 
of the different soils on prevalence or absence of the disease. A 
glance at the table on page — will show that the cane on practically 
every class of soil varying from sand to the heavy red clay of the 
uplands is subject to attack. 

In tests carried out in the plant house three types of soil were 
used, a pure white sand such as was being used for building opera- 
tions, the black loam used in propagating work at the station, and 
a red clay subsoil. Cuttings used were from diseased and normal 
stalks of B-3922, cut to two buds or internodes per piece, and all 
dipped in Bordeaux mixture fifteen minutes before planting. There 
was never at any time any effects as far as absence, presence, or rela- 
tive virulence of mottling was concerned. Diseased cuttings pro- 
duced diseased stalks, the normal cuttings healthy stalks, and there 
were no changes throughout the season. There was of course great 
variation in the amount of growth, plants in clay and sand thriving 
poorly except when aided by chemical fertilizer. 

A very striking illustration of the conclusion that the nature 
of the soil has no effect on the disease is furnished by the field in 
which the disease first appeared near Rio Piedras. The soil was 
very fertile, had not been planted to cane for many years and gave 
what was probably the highest yield of any field on the north coast. 


Rainfall and soil moisture. 

Of the considerable number of theories suggested, the one which 
warrants most serious consideration is the relation of the weather, 
and more particularly the periods of drouth to this epidemic. The 
records of the United States Weather Bureau have been studied 
in an endeavor to correlate the rainfall, or perhaps the lack of rain- 
fall, with the inception and spread of the mottling, but this has 
not not been very successful. The greatest difficulty has been in 
the nature of the rainfall of Porto Rico, which in large part comes 
in the form of numerous local showers. This means that there is 


the greatest possible variation in precipitation from locality to lo- 
cality. For instance, one valley may be suffering from a prolonge | 
drought while only a few miles away there may be a sufficiency of 
moisture. Therefore if it is found, for example, that the precipits- 
tion for Camuy was at a certain figure for any month, it does not 

















YELLOW STRIPE OF SUGAR-CANE. 39 


mean that the country directly to the south had the same amount 
of rain by any manner of means. 

Considering the annual precipitation, it is found that Arecibo 
tends to approach the average for the Island, that Isabela and 
Camuy fall below, often as much as twenty inches, but that Utuado 
and the districts east of Arecibo exceed the average. <A_ serious 
drouth in the region from Arecibo west occurred in the first months 
of 1916, and was preceded by excessive rainfall during the latter 
part of 1915. <A similar drouth occurred during the first part of 
1917 but was not so serious as that of the preceding year. This 
state of affairs was sufficient to bring on a serious condition of the 
eane. In fact it had a tendency by the yellowing of the leaves and 
stunting of stools to obscure the mottling. That it had no relation 
to the disease is evident when it is considered that Utuado and other 
districts which had not suffered from these severe drouths, at least 
as far as the weather records show (Utuado had 21.70 inches of 
rain from January to April, 1916), have also been severely infected, 
and that although the season of 1917 was normal as to precipitation 
the disease spread unchecked. 

An experiment to test the effect of the moisture neni was set 
up in the plant house in the same manner as already described for 
other tests there, using black loam soil. Half of each of four series 
of ten cans was planted with normal cuttings, the balance with dis- 
eased. The resulting plants were allowed to grow several months, 
being watered normally or about once a day on the average, until 
they were about eighteen inches in height and well established. Be- 
ginning at this period one series of ten cans was watered to satura- 
tion, drainage holes in the bottoms being plugged; one series was 
watered normally ; and two series were watered only at long inter- 

vals when wilting became pronounced. About one quart at ten day 
intervals was the amount given this series. At the end of two months 
one of these two latter series was treated as the first one, the soil 
being kept practically saturated for the duration of the experiment. 
The purpose of this was to simulate the alternation of drouth and 
long periods of rainfall, such as are of common occurrence in the 
western sections of the Island. 

Normal cane made the better growth in all cases, which condition 
was particularly noticeable in the heights attained during the first 
few months. Canes under drouth conditions practically ceased to 
grow with the cutting off of the water supply and most of the series 
finally died. Much the same effects resulted in the saturated series. 


There were no other results. 










































40 JOURNAL OF T'HE DEPARTMENT OF AGRICULTURE. 


A similar experiment was set up in three series of ten cans each 
using the red clay subsoil. These were treated in the same fashion 
as the preceding except that the alternation series was omitted. It 
was necessary to supply chemical fertilizer to secure satisfactory 
growth even in the normally watered series. Here again there was 
a dying of plants in dry and saturated soils of both normal and 
diseased lots. 

The same series planted in a white sand gave the same results, 
it also being necessary to supply fertilizer to secure growth. Based 
on the results of the field survey and the plant house experiments 
it is a safe conclusion that water supply has no direct influence on 
the mottling disease. 


NATURE OF THE DISEASE AND POSSIBLE CAUSES. 


The endeavor to learn definitely the nature of this disease has 
proven rather baffling, and has led to experiments and studies along 
a considerable number of lines. Several theories have been tenta- 
tively considered from time to time, each of which has in turn given 
way to another as more facts came to hand. The progress of these 
studies will be briefly reviewed with the addition of such data as 
has been obtained since the writing of the last report. 

It was first thought that the trouble was a manifestation of dete- 
rioration or running out of an old long established variety, the 
situation being accentuated by unfavorable climatic conditions. This 
view was soon abandoned because of the spread of the disease to 
other varieties and to districts where weather conditions had been 
normal. Much of this deterioration trouble is present, however, in 
all sections and represents a problem of no little importance, but 
is so sufficiently distinct that confusion need not arise. 

Degeneration, a theory advanced at one time to account for the 
disease, likewise proves unsuitable in the light of further facts as 
the following exposition will make clear. 


Inoculation tests. 

Although all inoculation tests made in the preceding year gave 
negative results, field evidence proved rather conclusively that the 
disease had means of transmission other than by infected seed pieces, 
so that it seemed desirable to make further trials at artificial transfer 
of the disease. 

In the first experiment a typical mottled stalk was ground in 
an ordinary food chopper and the expressed juice used as the in- 
oculum. A hypodermic needle was employed to make inoculations. 





Tallos Cancerosos. Variedad Cavangerie 
( Cafia de Vino) 


Cankered Stalks. Variety Kavangerie. 




















YELLOW STRIPE OF SUGAR-CANE. 41 


A convenient plot of cane (Yellow Caledonia) some distance from 
any infection areas was selected and twenty-two stalks in all stages 
of growth from six inches in height to mature canes were inocu- 
lated. The punctures were made in some instances in the buds, in 
others at the growing point, and in still others into the internodes. 
Corresponding stalks were punctured as checks but not inoculated. 
None of these stalks, neither the inoculated nor the checks, has shown 
any signs of mottling. 

As a second test another diseased stalk was similarly ground to 
furnish the inoculum and the material applied as before to canes 
of the variety B-3922 growing in the plant house. Twelve lots were 
inoculated in various ways with corresponding checks. Results were 
again negative. 

Three series of these experiments were made the year before the 
varieties involved being Otaheite (Blanca), Yellow Caledonia, Ra- 
yada, D-117 and B-376 for a total of over one hundred inocula- 
tions. No positive results were obtained at the time, nor have any 
of the stools shown mottling in the present season. 

Acting on a suggestion that the mottling might be similar to 
bean mosaic in its reactions, a series of tests was made in the plant 
house by inserting small bits of diseased tissue into various parts 
of normal canes. <A set of inoculations was also made by rubbing 
growing tips of a number of healthy stalks after a diseased tip had 
been crushed in the fingers. It had been found by investigators 
that the bean mosaic could be transferred in this manner but not 
by using the expressed juice. There had been no developments from 
these tests at the last observation. 


Chemical tests of the juice. 

Limited tests of the juice of diseased canes were made in the 
division of chemistry of the station, from canes furnished by this 
division, with particular reference to the glucose ratio and a pos- 
sible reduction in sugar content. It has not been apparent at any 
time that data of any great bearing on the problem was obtainable 
( in this direction, but it was considered desirable to try out this 
possibility in common with all others. 

The results of some of these analyses are given in the following 
table: 

















42 JOURNAL OF THE DEPARTMENT OF AGRICULTURE. 


Table III.—Chemical Tests of the Juice of Diseased and Normal Canes. 





Date 1917 | Condition Source Variety ene Sucrose Purity 
| 
‘lo re Normal ...... Cambalache..) Rayada... 12.23 6.47 52.9 
Ue Sere Diseased...... Cambalache.. Rayada... 12.43 6.83 54.9 
September 29,..... | Normal ...... Rio Piedras, .) B-376...... 11.51 6.43 57 60 
September 29...... | Diseased...... Rio Piedras,, B-376...... 11.51 6.84 59.42 
October 17......... Normal ...... Rio Piedras, .| B-208.,.... 13.88 10.40 74.9 
Lo le > ae Diseased...... Rio Piedras, .| B-208..... 12.68 8.75 69.0 
November 8....... Normal ...... Kio Piedras, . 3925 15.84 12.47 78.72 
November 8,...... Diseased...... Rio Piedras, . 14.47 12.57 86.86 
November 8....... Normal ,..... Rio Piedras... 14.88 11.89 79.90 
November 5....... Diseased... .... Kio Piedras, . 14.98 12.20 81.44 








It is realized that handmill tests of the juice of one or a few canes 
only cannot be taken as conclusive, but it is thought that these tests 
are sufficient for comparative purposes. It seems apparent that canes 
in the first stages of the disease, that is before the cankers and split- 
ting are present, are but little affected, as far as their sugar content 
and purity of the juice are concerned. Losses would be due to a 
reduction in tonnage as indicated in the experiment by Lyon already 
described. In fact as will be noted from the table diseased canes 
in some cases actually showed a higher sucrose content than corre- 
sponding normal canes. Individual differences in age of cane or other 
factors explain this, however, since the two lots of cane always came 
from separate stools of course. It is interesting to note that at least 
one Central reported the same state of affairs in their mill tests 
in contrast to others which claimed a high glucose ration. As al- 
ready noted this high glucose content is thought to be due to the 
fact that in advanced stages the openings in the rind splits and 
eankers) permit the entrance of bacteria and fungi with resulting 
fermentation. 

As a final test along this line two lots of cane of the variety 
B-3922, one diseased and one normal were cut, care being taken 
to obtain canes as nearly of the same age, size, and other conditions 
as possible. Two canes of each of these lots were analysed by Mr. 
J. Lépez Dominguez daily as long as the samples lasted. The re- 
sults are given in the following table: 














YELLOW STRIPE OF SUGAR-CANE. 


“~~ 
~ 
> 

= 
> 
% 

> 
i) 
s 
¢<) 
i} 
= 
~ 

— 

by -4 
© 

~ 

~ 
~ 





FIG. 6.—Leaf spot of cane. 











44 JOURNAL OF T'HE DEPARTMENT OF -AGRICULTURE. 


Table IV.—Chemical Tests of Diseased and Normal Canes. 





Date 17 Condition Brix Sucrose | Purity 


November 


| 
I | 
Normal 14.90 11.96 | 82.96 





November LT REG pene 15.10 12.00 79.47 
November Sc. | ie jf 13.80 10.55 | 76.44 
November ET Ea eee ee 14.10 10.74 | 76.17 
November hc | er 15.20 11.07 | 72.82 
November Diseased........ “ae 14.20 10.24 | 72:11 
November BMA cyciccicle ests Sete 13,00 5.42 | 12.07 
November (aaa 13.58 9.45 | 60.58 
November Cc Se 14.76 9.37 | 63.48 
November ee, OI 14.00 8.40 60.00 
November Ll mee 14.93 10,20 68.31 
November Diseased... ..........s0c- 13.53 8.71 64.37 
November 2 PN ba os Sex os aise 15.8 10.8 | 68,35 
November 20., TS ER Saree. 15.2 10.06 | 66.18 





ITere again no constant differences appear, confirming the results 
of the previous tests. 


Relation of fungi or bacteria. 

Lecves.—From the appearance of affected leaves, the presence 
of funei or bacteria as causative organisms would not ordinarily be 
suspected. Early in the work sufficient examinations were made to 
clear up any doubts as to this point. Microtome and free-hand see- 
tiers failed to show any differences between normal and = diseased 
leaves other than the absence or deficiency of chlorophyll in the 
chlorotic spots. A number of attempts were made to obtain bv the 
plating cut process a responsible organism but none appeared. Those 
forms obtained did not oceur uniformly and were either plainly 
seprophytic or the characteristic symptoms produced by them on 
the leaves when parasitic were well known. They were found on 
the older leaves for the most part, recently unfolded leaves proving 
eonerally free of any organism. 

Particular attention was given on field trips to the relation, if 
any, of the various leaf-spot diseases to mottling but it was never 
possible to find any such connection. There was practically as much 
spotting due to Leptosphaeria sacchari and Helminthosporium sac- 
chari on normal as on mottled cane. 

Stalks.—Sufficient work to amply justify the conclusion that or- 
ganisms attacking the stalk were not directly involved as causes of 
the disease were carried out last year, and may be here briefly 





reviewed. 

The absence of any distinctive internal symptoms in the form 
of rot or gumming made it very doubtful from the first whether a 
parasite would be present. A special search was, of course, made 
for rind disease (Melanconium sacchari), red rot (Colletotrichum), 

















YELLOW STRIPE OF SUGAR-CANE. 45 


gumming (Bacterium vascularum), or other parasitic stalk diseases. 
Suffice it to say that while isolated cases have been found of the 
common stalk diseases of Porto Rico (gumming does not occur here) 
they have not been present to even an extent where appreciable 
damage was being caused, nor was there any connection with the 
mottling. 

The common, easily recognizable fungi having been eliminated, 
attention was turned in the laboratory and in the pot cultures to 
an attempt to find a more obscure parasite or other cause. Tissue 
cultures and damp chamber tests were made from time to time, both 
of cankered stalks and of stalks which were normal appearing ex- 
cept for leaf mottling. Cultures of representative cankers made 
November 1 gave Valsa sp. and Trichoderma lignorum. On Novem- 
ber 11, tissue cultures of stalks of B-208 and Yellow Caledonia 
proved sterile. In sterile moist chambers sections of the stalks pro- 
duced a growth of Trichoderma, and in one instanee of Schizo- 
phyllum. Seven lots of cankered canes were tested in damp chambers 
under sterile conditions, beginning December 26. Of these. two 
remained sterile, one produced Trichoderma, and four were over- 
erown With Aspergillus niger, but were otherwise sterile. 

Similar tests were made in January of portions of mottle-leafed 
and cankered stalks brought in for planting tests. Pieces of eight 
stalks of Otaheite, Rayada, B-3412, and Sarangola produced only 
the customary saprophytes mentioned above. 

A further series of tissue cultures was made, all precautions to 
obtain sterile conditions being taken. Short sections of stalks were 
immersed in mereurie bichloride (500-1) for several minutes, rinsed 
in sterile distilled water, and in the culture chamber, fragments 
removed with sterile instruments for planting in beef agar plates. 
The majority remained sterile until completely dried out, Aspergillus 
niger appearing on some, but quite plainly as a contamination. 

To still further examine into any possible relation of the more 
commonly occurring fungi, several imoculation experiments were 
carried out. In the first of these Colletrotrichum falcatum was used 
as the inoculating agent, and D-117 cane as the host. Ten stalks 
were punctured with a hypodermic needle and material from a 
pure culture inserted. Ten other stalks were similarly prepared, 
except that sterile water was used in place of the fungus. From 
time to time inoculated stalks were cut and examined. At no time 
was there any evidence of even the beginning of red rot. The only 
abnormal sign was the red discoloration around the puncture, such 
es cesurs areund any wound. The checks remained without change. 











46 JOURNAL OF THE DEPARTMENT OF AGRICULTURE. 


In addition to these laboratory experiments several extensive 
field tests were carried out with Colletotrichum falcatum and other 
fungi commonly occurring on diseased cane. As mottling did not 
appear in any of the canes grown in these experimental plots it was 
evident that the fungi were saprophytic only, or at least had no 
connection with the mottling. These tests are reported in detail 
in the 1916-17 report. 


Nature of the cankers. 

The cankers or lesions on the stalks of badly diseased cane are 
apparently the result of the general weakening of the stalks. Since, 
as has already been mentioned, they are first noticed before the leaf- 
sheaths loosen, and hence before fungus spores or bacteria could 
have penetrated, they are not primarily due to the action of fungus 
parasites. This conclusion is borne out by the cultural studies made. 
The various fungi, which are always present in abundance in and 
about the cane stools, doubtless are washed down as spores or my- 
celial fragments behind the leaf-sheaths as soon as these latter 
become loosened. The lesions already formed are then enlarged in 
size and depth by their action. They cannot, however, be concerned 
to any extent as primary agents since otherwise innumerable cases 
of red rot, rind disease, and other stalk rots would be found, the 
fungi causing these being omnipresent in all cane fields. Inocula- 
tions in an attempt to produce cankers have failed. 


Bud tests. 
While taking notes on the experiment in the plot of B-3922 a 


considerable number of stalks were found from time to time which 
showed mottling on the upper leaves only. When a new stalk he- 
came diseased, or rather when it first gave external evidences of 
being diseased, the mottling symptoms first appeared in the unfolding 
leaves. All succeeding leaves would then be mottled but the lower 
leaves would continue green and unchanged. At the transitional 
region one or more leaves might be marked in part only, for instance 
for a few inches out from the base, for half the length, or on one 
side of the mid-rib only. 

All such stalks encountered were tagged at the point of transi- 
tion and after growth had progressed long enough to form a number 
of nodes above the tag, they were cut for planting tests. These 
were conducted in the plant house, and the aim was to ascertain 
as to whether or not the entire stalk contained the virus of the 
disease, or only the portion above the transitional area. The buds 
were numbered from the bottom up, the stalk cut into two-eyed 

















YELLOW STRIPE OF SUGAR-CANE. 47 
cuttings and the ends tarred. Ordinary soil was employed in which 
eane had not been previously grown. 

Details of the behavior of buds from several characteristic stalks 
will suffice to show the course of the experiment. 

Stalk No. 124.—Cankered above the point where mottled leaves 
occurred. Shoots from all eyes mottled. 

Stalk No. 175.—Cankered and split above the transition. All 
buds produced mottled shoots. 

Stalk No. 2.—No cankering, though the stalk was not normally 
plump between the nodes. All buds produced mottled shoots which 
remained so throughout the season. 

Stalk No. 193——Cankers and shrinkage of the stalk present over 
several internodes below the transition. All shoots produced were 
mottled. 

There were no exceptions to this sort of behavior in any of the 
series of plantings made of stalks of this nature. 


Effect of chemical applications. 

One of the possibilities that immediately suggested itself when 
studies of the disease were undertaken was that it was due to lack 
of iron, or to inability of affected plants to assimilate sufficient iron 
in the presence of an excess, of some other chemical. 

Potted specimens were sprayed with a four per cent solution of 
ferric ammonium sulphate, iron potassium sulphide, and ferrous 
sulphate, the only iron compounds at hand at the time. There were 
absolutely no results from this treatment. 

In a latter experiment ferrous sulphate alone was used. Of ten 
plants, two were left as checks untreated, four were sprayed with a 
ten per cent solution and four with a five per cent solution. Several 
grams of the crystalline salt were placed in the soil of each pot. 
This treatment was repeated three times at intervals of a week. 
There having been no observable results after a lapse of a month, 
125 cubie centimeters of ten per cent solution was poured on the 
soil of the first four, and the same quantity of five per cent solution 
on the other four. Again there were no results and the cane was 
cut to permit it to ratoon. After another month the solutions were 
again applied as above to the new shoots, but without results. It 
was apparent that the disease was not related to the chlorosis dis- 
eases of pineapple or cane, which have been clearly shown to be due 
to lack of iron in the soil, or to inability of affected plants in the 
presence of an excess of iron to assimilate sufficient iron for normal 


growth. 








48 JOURNAL OF THE DEPARTMENT OF AGRICULTURE. 


Copper sulphate was also tried with the view in mind that it 
might serve to restore normal green color to mottled leaves. Two 
plants were sponged with a two per cent solution, two with a five 
per cent. A quantity of each strength was also poured on the soil 
of each pot. This was repeated twice over a period of two months, 
but without the slightest effect. Mottled shoots remained mottled 
at all times. 


Manner of transmission of the disease. 

A number of tests were made to ascertain as to whether or not 
the disease was carried over in the seed. For this work five-gallon 
oil cans only were available, which were rather small for growing 
cane to maturity. In all of these plantings the seed pieces were 
recut prior to planting, soaked fifteen minutes in Bordeaux mix- 
ture and planted immediately. Unless otherwise noted, the soil has 
been a fair quality black loam such as is used in all propagation 
work at the station. 

The first planting was made on December 9, seed for checks 
being taken from fields on the station grounds. Examinations were 
made from time to time as to the presence or absence of mottling, 
and the number of shoots produeed. Neither in this experiment 
nor in any of the others was there any apparent correlation between 
the disease and the number of shoots produced. The results of the 
first and last examinations only are given unless intervening dates 
showed facts of importance. 


Table V.—Results of First Series of Pot Experiments. 








Group Can Soil | February 8.1917 | July 25, 1917 
No, | 
| 
| 
Sterilized (steam)....) Leaves mottled ......| Leaves mottled 
2 | Untreated........... | Leaves mottled ..... | Leaves iottled 
A eeeeeeee eee eeeees Si Pinmtreared. ....<. sess Leaves mott'ed ......| Leaves mottled 
1 | Untreated ........... Leaves mottled ...... Leaves mottled 
{ 5 | Untreated .... ..... Leaves mottled ......; Leaves mottled 
‘ ! 6} Sterilized........... Leaves mottied ...... Leaves mottled 
Boveeeeceeeee cence ; 7 | UNGTORIEG: ... «occ Leaves mottled Leaves mottled 
6 | Untreated .............- Leaves mottled ..... Leaves mottled 
{ % | Sterilized ...... ... | Leaves mottled ...... Dead 
SS ee ee ene } iO] Untrested. ....4..5.5. Leaves mottled ......| Leaves mottled 
| ii | Dmtreated...... <5... in ee ren een eeae ee 
12 | Untreated,,.......... | Leaves mottled ...... Leaves mottled 
D 13 | Untreated........... | Leaves mottled ...., Leaves mottled 
ark ee 14 | Untreated,...........) Leaves mottled .....} Dead 
15 | Sterilized.,.......... | Leaves mottled ...... | Le»ves mottled 
{ 16 | Sterilized....... : | Leaves not mettled,.; Leaves doubtful 
B cscs seeeescceeee 17 | Untreated........... Leaves not mottled __| Leaves not mottled 
H 18 | Untreated... Leaves not mottled, .| Leaves not mottled 
f 19 | Sterilized............- Leaves not mottled, .| Leaves not mottled 
“a ee ) 901 Detrented ......se.s. Leaves not mottled, .| Leaves mottled 
eras oe | | Leaves not mottled 


21 | Untreated .......ccess Leaves not mottled,. 





. Yellow Caledonia.—Seed obtained from near Arecibo, plant 


-— 




















YELLOW STRIPE OF SUGAR-CANE. 49 


cane, seed for which was obtained from this station. It had been 
planted in soil said never before to have been in cane, although sur- 
rounded by diseased fields. The field showed about thirty per cent 
of mottling, and later the first ratoons were a total failure. This 
test was made with uncankered stalks, the leaves of which were 
mottled. 

B. Rayada.—From near Arecibo, typically mottled and cankered, 
nodes shrunken. 

C. Yellow Caledonia—Same as A, except that the stalks were 
lightly cankered, and but little shrunken. 

D. Same.—Stalks very badly cankered and shrunken. 

E. Check. D-117.—Seed from s‘ation fields. 

F. Check. Yellow Caledonia.—From station fields. 

Soil for the second experiment (planted December 13, 1916) 
was a heavy clay obtained from a field in the Arecibo district, which 
had been abandoned to cane culture because of the disease. A por- 
tion of this was sterilized (cans Nos. 1, 2, 3) by steam (one hour 
at about sixty pounds pressure), and the remainder untreated. The 
seed used was the same as that of the first planting. 


Table VI.—Results of Second Series of Pot Experiments. 





! 
Can No. | seed February 8, 1917 July 25. 1917 
| 


Leaves mottled || Leaves mottled 
Leaves mottled ..| Leaves mottled 
Normal... ccs: Leaves mottled 2 
Leaves mottled ,.) Leaves mottled 
Leaves mottled ,.| leaves mottled 
NORMALE ....6555. Normal 

NOFMIQE © %. ccc: Leaves mottled 
MORMERE cscs a Normal 

Leaves mottled || Le aves mottled 


Leaves mottled ..; Leaves mouled 
Normal Norma] 











1 Soil sterilized. : ; 
2 Mottling was first noted on two out of six shoots on March 6, this proportion con- 
tinuing until June 25, by which time all were affected. 


On December 23, another set of plantings was made in order to 
obtain further data on canes which were being examined in the 
laboratory at the time. Steam sterilized soil was used. 

1. Catia de vino (Cavengerie).—A stalk from Camuy, apparently 
normal but from a stool other stalks of which were showing mottling. 
In the local test all shoots from buds of this stalk remained normal. 

2. B-3412.—Stalk of mottled cane obtained near Camuy, seed 
for which had been sent from this station. Most of the field was 
showing mottling. All shoots from the piece planted were mottled. 














JOURNAL OF THE DEPARTMENT QF AGRICULTURE. 


3. Otaheite—From near Camuy, a field showing 100 per @ent 
infection. All shoots produced mottled. 

4. Crystallina.—A diseased stalk from near Camuy, field showing 
about fifty per cent of disease. All shoots mottled. 

A fourth and final planting experiment was started January 5, 
using the ordinary station potting soil untreated. The seed was 
all obtained from various badly diseased fields near Central Alianza. 


Table VII.—Results of Fourth Series of Pot Experiments. 

































| | ‘ 
Can ' Tarlety ‘ondi Pseed | Fe 917 | July 25, 
No. Variety Condition of seed | February 8, 1917 1917 
| 
| 
$. AMMO IS VIDOS.. cociccssee! Sesee WOLKMAl .. is scccss ...| Normal Mottled 1 
la of AD FUN) 6 icsc scecniose vee cine i Ee ae Mottled Mottled 
DP cic us-anaie | Bamboo... .| Cankered .... Mottled .... .| Mottled 
ih ovecesen | Bamboo..... Diseased . ..| Mottled ., Mottled 
eas Caia de vino........ ...| Normal .. ..| Normal .. .| Normal 
ee SPE. sug Suk sicsicnshesseeeeene ee ey Normal ,. Normal 
EEE | Bamboo...............+++++.-- | Cankered, mottled... Mottled Mottled 
4a.........| Bamboo (same stool).......... MIO 5s vecacesenes Normal Mottled 
| RRS 1 CMO OO WAND 5 occ oseccccseess NI eek isicspaid siete Mottled Mottled 
ee ; Cafia de vino (same stool)..... MOCIOG, 6 kcccecocses Normal (?)....... Doubtful 
| KE | Catia de vino (same stool)..... Cankered, mottled... Mottled........... Mottled 
Yellow Caledonia.............. oe on, MOPMR) oooc6s cscs Normal 
.| Yellow Caledonia (same stool)| Cankered, mottled...) Mottled .......... Mottled 
Bi ee ee ee DORON 055 peewee cee | Mottled .......... Mottled 
Rayada (same stool) .......... ME opi ouceccs caus | Mottled .......... Mottled 





1 Changed to diseased condition during May. 


These results seem to warrant certain conclusions as to the beha- 
vior of diseased canes, although it is recognized that they are by 
no means conclusive. However, even from the limited tests made 
it is quite certain that all cane shoots springing from seed pieces 
which were from cankered or mottled-leaf stalks will be diseased in 
spite of soil sterilization and disinfection of the seed. One exception 
only occurred in our tests, and that one was very doubtfully normal. 

Of the various seed pieces taken from apparently normal stalks 
or stools which were diseased in part, about half produced normal 
shoots and the remainder mottled. This phase of the experiments is 
rendered uncertain by the fact that a stool of cane under the plant- 
ing system usually employed in the western portion of the Island 
consists of the growth from about four seed pieces, and since it is 
apparent that the disease is transmitted through the individual seed 
pieces, it is undoubtedly a fact that many instances of. planting of 
one, or two. diseased seed pieces together with normal ones aecounts 
for the presence of both types of stalks in the same stool. After 
the first cutting it is difficult to trace the separate plants composing 
the stool. There have been found, however, examples of normal 
and mottled shoots arising from the same rhizome. The virus of 








it 











YELLOW STRIPE OF SUGAR-CANE. 51 


the disease is present in all such stalks whether they show outward 
signs or not, and this fact will aecount for the results obtained in 
the above described planting tests with apparently normal stalks 
from mottled stools. 

The above experiments were those conducted in the previous 
season but the results have been confirmed most conclusively by all 
work since that time. All plantings, without exception, of cane 
from mottled stools made in the plant house and field experiments 
to a total of several hundred produced typically mottled shoots. 

The following results from an experiment by Mr. Bourne of Gua- 
nica Central add further exact data. 

“In January 1918, 100 cuttings taken from diseased stalks of 
B-3922 were planted in Tablén No. 8 at Santa Rita alongside of 
100 euttings taken from absolutely healthy stalks of the same va- 
riety. Both kinds of cuttings gave practically the same germination. 
Early in March an examination was made and it was found that 
all the shoots from the diseased cuttings had the mottling disease 
while those from the healthy cuttings had no sign of the disease. 
The diseased cuttings were then dug up and destroyed and the 
space replanted with healthy cuttings which have all germinated. 
At the time of writing an examination was made of the shoots from 
the healthy cuttings and about 1.7 per cent of them have developed 
the disease. From this experiment the importance of carefully se- 
lecting cuttings is very evident. It also proves that although a field 
is planted with healthy cuttings, the cane develops the disease after 
germination. ”’ 

It was very important to know before any system of control could 
be evolved whether the disease remained in the soil or not so that 
infection of healthy plants could occur from that source. To ascer- 
tain this under controlled conditions a series of ten mottled plants 
were selected in the plant house, the canes cut off at the surface of 
the soil and the underground portions cut sufficiently to prevent 
any ratoon growth. Seed pieces of normal B-3922 were then planted 
in each container. The stool from which the seed was obtained was 
marked as a check. No mottling appeared on any of the resulting 
plants throughout the season, nor on the following ratoons. The 
second series of pot experiments reported gives a further verification 
of this result. 

A series of forty pots was prepared in the same manner,- using 
mottled plants that had been used in other experiments, and _ re- 
planting with normal B-3922 as before. This test is still under 
observation but there has been no infection as yet of the new shoots. 











52 JOURNAL OF THE DEPARTMENT OF-AGRICULTURE. 


Similar experiments have been carried out in other sections of 
the Island on a field scale with comparable results. Some infection 
occurs of course in such cases but is explainable by aerial transmis- 
sion of the disease. 

It seems certain that the disease does not persist in the soil and 
that hence infection does not occur through the roots or rhizomes. 
It may, however, pass from the underground parts of a diseased 
plant to a healthy one where the two are in contact, although no 
certain evidence has been obtained on this point. 

It is thus absolutely certain that the mottling disease is trans- 
mitted by means. of diseased cuttings and this fact serves to explain 
in considerable part the spread of the disease from field to field, its 
appearance in fields never before planted to cane, and similar ques- 
tions. Not only has there been no attempt on the part of many 
growers to avoid use of such seed until the disease was present in 
overwhelming amount, but it has too often been true that such mate- 
rial has been planted in preference to healthy seed, since it was 
possible to sell the latter for grinding while the former was refused. 

The use of diseased seed will, however, explain the spread of the 
disease in part only, and it has become very evident as a result of 
field observations that there is some other method of transmission. 
In the absence of fungi or bacteria as causative agents whose trans- 
mission could be accounted for by wind, water, and other natural 
agencies it is rather difficult to arrive at any satisfactory conclusion. 

In the absence of any exact information the theory of insect 
transmission will be but mentioned and left for other workers to 
investigate and report upon. The writer feels certain that insects 
will be found which are capable of carrying the disease and this 
will then explain the appearance of the mottling in isolated valleys 
as well as accounting for its rapid advance from west to east. Wind 
cannot be considered as a carrier since the advance of the disease 
has been against the direction of the prevailing trade winds. It is 
supposed as another part of this hypothesis that these insects or 
insect occur primarily in the uplands, due to the presence there of 
wild host grasses, thus accounting for the prevalence of the disease 
in upland districts, and its rather peculiar behavior in jumping from 
valley to valley rather than working along the continuous coastal 


areas. The insects suspected in this connection are small sucking 


forms known as leaf-hoppers. Further support of this hypothesis 
is given in the discussion of the similar disease of sugar beets known 
as ‘‘curly-top,’’ where the causal relation of a leaf-hopper has been 
definitely proven. Aphids (Sipha flava and S. graminis), and the 




















YELLOW STRIPE OF SUGAR-CANE, 53 





mealy bug (Pseudococcus sacchari) have been also suggested, but it 
does not seem possible that these species which are so commonly 
present can be involved. They were present in abundance in the 
plant house in spite of precautions to prevent their entry, but there 
was no transferance of the disease, even though ants which carry 
them from plant to plant were also very abundant. 


Conclusion. 

With the mass of evidence presented it seems safe to conclude 
that the mottling disease of cane is an infectious chlorosis allied to 
similar diseases of cane, and other crop plants to be mentioned in 
following pages. It appears that it is not influenced by cultural 
factors, that fungi or bacteria are not present as causal agents, and 
that faulty assimilation or nutrition are not responsible. 

There is an infectious principle present in all parts of infected 
plants whether evident externally or not, which is transmitted in 
cuttings, and has some other mode of aerial transmission not yet 
ascertained. The causal agent may be considered an ultramicro- 
scopic organism as is known for some animal diseases and has been 
held responsible in the case of the tobacco mosaic. For those who 
do not believe in the possibility of such organism there is of course the 
theory of deranged enzymes. These will be found present of course 
in either event since enzymes not ordinarily present.in healthy cane, 
or abnormal amounts of those that are always present, would result 
from the attacks of the ultramicoscopie organisms. 

The weak point in this theory lies in the fact that it has not been 
possible to artificially transmit the disease to healthy plants, although 
there has been abundant field evidence that such transfers do occur 
in enormous numbers. This is held to be a problem that will be 
finally solved by changes in technique or manipulation of the virus. 
Similar difficulties have been had with other diseases attributed to 
similar causes. 


COMPARISON WITH DISEASES OF A SIMILAR NATURE. 


Yellow striping. 

A very interesting situation has arisen over the possible identity 
of mottling and a disease of Java and Hawaii known to the Dutch 
workers as ‘‘Gele Strepenziekte’’ or yellow striping as the name 
has been translated and applied in Hawaii. Lyon’ of the Hawaiian 
Sugar Planter’s Station in commenting on the writer’s paper (32) 
published in phytopathology first directed attention to this possi- 


1 Unpublished note. 











54 JOURNAL OF THE DEPARTMENT OF-AGRICULTURE. 


bility. In fact he went further insisting that they were identical 
and insinuating that the mottling was neither ‘‘new to Porto Rico”’ 
nor ‘‘alarming’’ as stated in the article in question. In passing it 
may be pointed out that the figures already given will testify to the 
alarming nature of the disease and it is quite certainly new to the 
Island. No claim was made as to its being new to any other part 
of the world. 

The ‘‘Gele Strepenziekte’’ was first mentioned by van Musschen- 
broek (37) in 1892 and in the following year Wakker (38) published 
on the same disease. Since that time there have been a number of 
other articles dealing with it in the Javan sugar-cane literature, 
which will be found listed in the bibliography appended. Both 
Wakker and Went (39), and Kriiger (18) deal briefly with it. It 
is said to have been first noted in Hawaii in 1909. The report of 
its occurrence there as well as a number of articles published since, 
dealing with the nature and prevalence of the disease have appeared 
in the Hawaiian Sugar Planter’s Record, which publication has not 
of course been available for reference. 

Concerning this yellow stripe disease Lyon writes as follows. 

‘It is an infectious chlorosis akin to the mosaic disease of tobacco, 
The causal agent operates at the growing point of the stem and in 
the unexpanded leaves which are rolled up in the spindle. Every 
lateral bud is infected as it is formed, so the disease is certain to be 
transmitted through cuttings from infected stalks. All varieties of 
cane growing in Hawaii are susceptible to this disease, but some 
much more than others. Likewise some varieties are far more sensi- 
tive to the disease than others, while others stand up well under the 
disease. 

‘‘In Java and Hawaii the disease is held under practical control 
by the selection of healthy sticks only for cuttings. 

‘“We have authentic records of the occurrence of yellow stripe 
disease in Hawaii, Fiji, Australia, New Guinea, Java, the Philippines, 
and Egypt.’’ 

With the exception of the brief paragraph in Kriiger’s work, 
none of the Javan references were seen until after the writer’s con- 
nection with the mottling work had been ended. Since then several 
of the more important ones have been obtained. In particular the 
plates in the article by Wilbrink and Ledeboer (40) were examined, 
and while these illustrate a phenomenon which resembles mottling, 
considerable doubt is still entertained as to the identity of the Porto 
Rican and Javan diseases. As far as the writer is concerned it has 

















YELLOW STRIPE OF SUGAR-CANE. 55 
not been thought advisable to jump to the conclusion that the two 
diseases are identical since specimens of the yellow striping have 
not been available for comparison. 

Lyon as noted has been positive of this identity basing his opinion 
on an earlier paper (32) of the writer. Since then it is reported 
that he has examined authentie Porto Rican material and confirmed 
his preventious diagnosis. 


Sereh. 

A very baffling disease of cane known as sereh has been present 
for many years in Java having been epidemic at one time. It has 
also been reported from other eastern cane-growing countries. It 
resembles mottling in some respects so that a short comparison of 
the two as to signs and characteristics will not be out of place. Dr. 
Smith’s (25) account of the Sereh is followed in the main. 

‘‘The sereh appears at first only sporadically; the year following 
one finds usually sereh plants everywhere and the third year the 
disease occurs in such severity (when no measures are taken againt 
it) that a failure of the crop results.’’ This corresponds very well 
to the course of the mottling disease. Other signs are also in close 
agreement, principal of which are the transmission of the disease 
from old plants to new ones by means of cuttings and a shortening 
of the internodes. On the other hand sereh is described with a 
number of points not noted in connection with mottling important 
of which are the presence of gum, slime, or crystals in the bundles 
or parenchyma tissues of the stalk, red staining of the bundles, 
yellow stripes (not mottling) of the leaves, excessive production of 
new shoots and roots above ground, the clinging of the leaves beyond 
the usual time of falling, and the dying of the foliage from below 
upward so that apparently the top of the cane is less diseased. Cer- 
tain other points, particularly the inclination to bloom early, have not 
been noted sufficiently well to be contrasted. In addition the Porto 
Rican disease possesses the very characteristic mottling and canker- 
ing of the stalks lacking in sereh. 

Every possible cause has been asigned by one worker or another 
to sereh, including plant and animal parasites to a_ considerable 
number, unfavorable soil conditions, wrong fertilizers, abnormal 
weather (drouth or excess of water), degeneration, dying of the 
roots, and improper cultivation practices. Workers on the disease 
have not settled on any definite cause as yet. 

Without, of course, ever having had any experience or direct 
knowledge of sereh, the writer is very much inclined to believe that 








56 JOURNAL OF THE DEPARTMENT OF AGRICULTURE. 


the mottling is a disease of the same nature and that both are due 
to ultramicroscopic organisms. 
Curley-top of sugar beets. 

A study of the literature on the ‘‘eurly-top’’ of sugar beets has 
shown many points of agreement with mottling, and the desease 
is of especial interest because of the relation of a certain insect as the 
earrier of the infecting agent. 

This is a disease which causes a distortion of sugar beet leaves, 
and a dwarfing of the plants with an accompanying reduction in 
yield. The losses vary from season to season but have often reached 
$1,000,000 in the western United States. Various theories have 
advanced from time to time but it was finally proven by Ball (4) 
that a leafhopper (Eufettis tenella) was responsible for transmission 
of the disease, and this conclusion has been verified by other workers. 
The insect in question is a native species found on a number of 
indigenous plants. Under certain conditions these insects pass in 
swarms to the sugar-beet fields, the curly-top developing soon after. 

It was found that leafhoppers ‘‘taken from wild plants did not 
transmit the disease until they fed on diseased hosts. Three hours 
on a beet rendered them pathogenic. It is probable that some wild 
plant carries the disease and leafhoppers coming from this plant are 
able to transmit it to the beets’’ (Ball). 

A most interesting feature of the work on this disease as it 
relates to the sugar-cane situation is the fact that it has never been 
possible to transfer the disease by inoculations, although it has been 
transferred by grafting. Mottling could of course also be trans- 
ferred in this manner if grafting of monocotyledons was possible. 


Tobacco mosaic. 

Probably the best known of the diseases of this class is the 
tobacco mosaic (2, 6), which oceurs in practically every tobaeco 
growing country in the world including Porto Rico. Affected leaves 
are mottled or blotched and in other than light cases distorted. 
Diseased plants are greatly stunted. Although the disease is highly 
infectious it has never been possible to find fungi or bacteria present 
as causal agents. It is very easy to transmit the disease to unaf- 
feeted plants by rubbing them lightly with the fingers after erushing 
a diseased leaf. In fact a great number of plants can be infected 
by an exceedingly small quantity of the virus, and it is by handling 
that the infection is spread to a large extent. 

Two theories are held as to the cause, one considers ultramicro- 
scopic organisms as the causal agent, the other enzymes or the 

















YELLOW STRIPE OF SUGAR-CANE. 57 


product of enzyme activities. The former seems the preferable 
theory. Insects, particularly one or more species of aphids have 
been demonstrated to be capable of carrying the virus. The strik- 
ing point of difference between tobacco mosaic and cane mottling 
is the failure to date to carry out artificial transmission of the latter, 
which is so easily done with the former. 


Spinach blight. 

Spinach blight (21) is a disease of the trucking region of the 
eastern United States, and has caused annual losses as high as $200,000. 
It is a specific disease characterized by a mottling and transforma- 
tion of the leaves, and a decided stunting of the growth. Diseased 
plants may occur in definite areas or they may be scattered over 
the field. 

Fungi or bacteria have never been found associated as causal 
agents. Nature of the soil, fertilizers, drainage, and other cultural 
factors, though all considered at different times have been found to 
be without any direct relation to the disease. 

It has been possible to transmit the blight by transfers of the 
juice of infected plants. Certain species of aphids and one in par- 
ticular (Macrosiphum solanifolu), have been demonstrated to be 
earriers of the virus and very interesting data has been collected on 
the relation of these insects to tle disease. The causal agent is con- 
sidered to be an ultramicroscopic organism. 


Peach yellows. 

Peach yellows has been known in the United States for considerably 
over a hundred years and has caused very heavy losses. It is char- 
acterized by a premature ripening of the fruit which is red spotted 
as well as being of poor quality. Slender abnormal appearing shoots 
are produced from the trunk, which bear pale yellowish-green leaves. 
Leaves on the normal branches may also be yellowish-green. 

No remedy has ever been found and infected trees invariably 
die after a number of years. Pruning of infected branches is always 
without avail, the virus being present in all parts of infected trees, 
even though portions appear normal. Control is secured by dugging 
out diseased trees as fast as they are discovered. 

The usual range of supposed causes including poor culture, wet 
or dry weather, wrong fertilization, insects, fungi, and over bearing 
has been gone over by various workers and all finally shown to be 
of indirect importance only. Here again the cause is doubtless an 
ultramicroscopic organism, although the enzyme theory has also been 
advanced. No insects have as yet been found which act as carriers. 














58 JOURNAL OF THE DEPARTMENT OF AGRICULTURE. 
It has been found possible to infect healthy trees by budding or 
grafting in diseased material. 


Cucumber mosaic. 

A disease, which has but recently made its appearance in the 
middle west where it is said to be the most serious disease of the 
crop present, is the cucumber mosaic. Typical mosaic symptoms are 
produced with a pronounced dwarfing or even final death of infected 
plants. 

It has been found possible to transmit the disease artificially by 
inoculations, and the striped cucumber beetle has also been proven 
a carrier of the infective principle. The disease has not been found 
to carry over in the soil or to be carried in the seed. A number of 
other species of the Cucurbitaceae have been found susceptible upon 
inoculation, but the same is not true with beans, tomatoes, potatoes, 
tobacco, or other non-cucurbitaceous plants. Those who have worked 
on the disease consider the cause to be still in doubt, but from the 
facts known concerning it seems to fall readily into the class of 
diseases under consideration. 


Potato mosaic and related abnormalities. 
Under this heading may be grouped for discussion those diseases 
or abnormalities of potatoes variously known as mosaic, curly dwarf, 
and leaf curl. By some workers they have been considered as merely 
varying phases of one disease and by others as distinct. They are 
sufficiently alike to indicate the same or closely similar causes. 

Leaf roll is characterized by an upward rolling of the leaflets at 
the tips of the branches or even of the entire plant in severe cases. 
The normal green color becomes yellowish often with a red tinge. 
Affected plants are stunted. In the eurly dwarf condition stems 
and leaves are shorter than normal, resulting in a dwarfing of the 
plants. The leaves are normal in color, but wrinkled and curled 
downward. The leaves of mosaie plants are, as the term implies, 
mottled and often wrinkled, resembling the same condition in tobacco 
leaves. All three of these abnormalities are transmitted through the 
tubers. 

Most of the investigators who have considered these potato disease 
have decided that they were non-parasitic, and have favored the 
degeneration theory as an explanation. Prof. Stewart has summed 
up his observations as follows: 

‘A striking feature of the study was the frequency with which 
the progeny of plants having normal foliage and high yield suddenly 
degenerated into worthless dwarfs.’’ 








Ne 


Oo! 
cu 


> Re 


a 


ae 

















YELLOW STRIPE OF SUGAR-CANE. 59 


‘‘There is no evidence that any one of the forms of degeneration 
named is communicable from one plant to another except through 
the medium of the seed tubers. They are not due to any parasitic 
organism, neither are unfavorable soil or weather conditions of the 
current season responsible. 

‘‘Neither normal foliage nor high yield is a guaranty of produc- 
tivity in the progeny of the following season. Degeneration may 
occur quite suddenly. 

‘Tt is unsafe to select seed potatoes from fields containing many 
degenerate plants. Even the normal plants from such fields are 
liable to produce worthless progeny.”’ 

In the report of last year the writer applied the above conclu- 
sions to the mottling disease and so asigned it to degeneration. The 
further evidence obtained since that time very effectively combats 
this tentative theory and likewise leads to doubt as to validity of 
degeneration as a cause for the potato troubles. They would seem 
to belong more nearly in the infectious chlorosis group of diseases. 
Such a theory better explains the various phenomena reported, such 
as the sudden appearance of disease or ‘‘degeneration’’ and its manner 
of spreading. 

A disease of beans also known as mosaic has been reported which 
clearly belongs to this group of diseases due to ultramicroscopic 
organisms or infectious virus. There are doubtless others as yet 
unstudied. 


ABNORMALITIES WHICH MIGHT BE CONFUSED. 


There are a number of abnormalities of cane due for the most 
part to non-parasitic causes which occur wide spread in Porto Rico 
and which can be and often are confused with mottling. 


Deterioration. 

This term is applied to the general unsatisfactory condition of - 
cane so common in Porto Rico and apparently in all other parts of 
the world as well judging from the literature, which varies from 
a mere lack of vigor to a ‘‘running out.’’ It is readily attributable 
to long continued cultivation of one variety, to unfavorable weather, 
to poor cultivation, and any other factor which tends to reduce the 
vigor of the plants. Harrison (13), who has given the most extended 
account of this matter, presents five principle causes for the deterio- 
ration or running out of cane varieties, basing his conclusions on 
observations of the downfall of the Bourbon variety in the West 


Indies. These causes are as follows: 











60 JOURNAL OF THE DEPARTMENT OF AGRICULTURE. 


‘*(1) Lack of vigor induced by continuous cultivation in the 
same soil, 

‘*(2) Continuous cultivation of the land to the same depth. 

**(3) No care being taken in the selection of suitable material 
for planting purposes. 

‘*(4) Spread of diseases. 

‘*(5) Changes in the varieties themselves.’’ 

The first three of these are primarily responsible for deteriora- 
tion, at least under Porto Rican conditions; the fourth has, as far 
as the present situation is concerned, been eliminated; and the fifth 
is an indefinite statement but one which applies very well and helps 
to explain such points as why certain varieties after thriving for 
a time begin to fail. 

The first symptoms as noted in the leaves may readily be confused 
with those of mottling. In facet, the spots or discolored areas can 
with certainity be distinguished only by their color, which is of a 
decided yellow rather than the white or nearwhite of the mottling 
disease. They are not to be differentiated from the yellow spotting 
described on a following page. 

When the unfavorable circumstances persist, the deterioration 
becomes more marked, resulting in a dwarfing of the stools, dying 
of the leavesand roots, and general appearance of unthriftiness. It 
becomes especially marked in each succesive ratoon crop, and if the 
field be not abandoned an exceedingly large number of stools die 
each season. In these advanced stages the rhizome and base of 
the plant will be thoroughly rotted and permeated by the white 
mycelium of one or more fungi (Himantia stellifera occurs most 
commonly). It is this situation that has lead to the designation 
of this condition as ‘‘root disease’? by many writers. 

Deterioration is wide spread in Porto Rico, being especially com- 
mon in its early stage for instance, where unsuitable varieties are 
being grown, where cultivation and fertilization have been delayed 
in heavy soils, or during periods of drouth. The fact that there is 
a recovery (that is the new leaves are normal) from this stage and 
that the growers have confused it with mottling, probably explains 
certain persistant claims that the latter disease has been ‘‘eured’’ 
by fertilization or other methods. 


The former has always been a prominent factor in cane cultiva- 
tion in the western portion of the Island because of drouth and 
cultural conditions prevailing there, and is still, of course, very 
much in evidence and still causing heavy loss. Innumerable eases 








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Jatt 
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Jav 
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(16 


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Ma 
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she 
sta 
ahi 
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YELLOW STRIPE OF SUGAR-CANE. 61 


occur Where it acts in connection with mottling, but sufficient observa- 
tions and tests have been made to indicate that it is distinct from the 
latter malady. 

The presence of a non-parasitic type of root disease resulting in 
deterioration has been recognized by other workers, particularly in 
Java. Wakker reports an hereditary constitutional disease charac- 
terized by yellow spots in the leaves, and Kamarling and Suringer 
(16, 17) studied a root disease due to a compacting of a heavy soil. 


Root disease. 
In addition to the above, there is another and somewhat similar 


disease quite clearly, however, parasitic in its nature. Several fungi 
occur in and about cane stools suffering from this type of disease. 
Marasmius sacchari has been the one most commonly held responsible 
but the writer does not believe that it is at all concerned. The 
stellate crystal fungus (Himantia stellifera) and the granular leaf- 
sheath fungus (Odontia saccharicola), the latter probably the perfect 
stage of the former, are of even more common occurrence. As 
already noted elsewhere (15) the entire matter of the relationships 
of these various fungi, and their connection with root disease of cane, 
is a subject requiring definite experiments under controlled condi- 
tions before exact statement can be made. 

In typical cases of root disease there is no spotting of the leaves, 
other than that they are very susceptible to Leptosphaeria. They 
die back uniformly from the tips and along the margins, the lower 
ones dying first. For some time, except for the dead and dying 
roots and leaves, no other symptoms appear. Finally, however, one 
or other of the fungi mentioned grows up around the stalk binding 
the leaf-sheaths rather firmly together with a white mycelial mat. 
A musty odor is present. Practically none of this disease has been 
encountered in the territory where the mottling prevails. 


Chlorosis. 
Prominent among the abnormalities which have been confused 


with mottling is the whitening or yellowing of the cane leaves known 
as chlorosis which occurs only in a limited area on the south coast. 
This trouble is found generally in small definite areas from a few 
feet to an acre or so in extent. All canes in the given area will be 
affected so that the spots stand out prominently from the surround- 
ing cane. Individual stools may be considerably stunted, and the 
leaves yellow to white in color. The discoloration in this ease is 
uniform with no trace of a mottled appearance. 

The cause has been definitely shown by Gile (12) to be due to 











62 JOURNAL OF T'HE DEPARTMENT OF AGRICULTURE. 


inability of the cane plant to assimilate sufficient iron due to the 
presence of an excess of lime in the soil. This trouble can be over- 
come to some extent by applications of manure and ferrous sulphate 
applied as a spray. 


Yellow spotting. 

Another very common abnormality of cane leaves and one which 
is wide spread in all parts of the Island is what has been designated 
as yellow spotting. Certain varieties notably Yellow Caledonia and 
B-1809 are very susceptible to it. It is characterized by small 
yellow spots with indefinite margins very much resembling the 
markings of mottling except that the latter are more nearly white, 
and generally more linear. A further point of difference lies in the 
fact that this yellow spotting attacks the lower leaves first, new leaves 
issuing from the bud being always of normal color. Yellow spoted 
leaves are very subject to Leptosphaeria, and other leaf spots, and 
very often fall prematurely. 

This condition in the early stages yields to an increase in the 
moisture supply, and especially to fertilization and improved cultiva- 
tion. It is not transmissible through the seed, except in so far as 
a general tendency to the trouble is concerned when conditions are 
not of the best. This phenomenon is to be considered as the first 
stage of deterioration. 


White-striping. 

There is a striping of cane leaves, already referred to as a chimera, 
which is common particularly on certain varieties. This consists of 
stripes of varying width, rarely including the better part of an 
entire leaf, and running the length of the blade. These stripes are 
of non-parasitic origen, and result from little understood reactions 
of a cell or group of cells at the growing point of the stalk. The 
same phenomenon is common on Indian corn (Zea mays). 


Mite injury. 

At one point of the work with the cane in the plant-house a phe- 
nomenon appeared on many of the plants which was practically 
identical with mottling. This was due to an undetermined mite 
very similar to the common red spider which is so common as a 
green house pest. In several instances the only way in which it was 
possible to make certain which was which was to unroll the young 
still-folded leaves at the center of the plant. If a mottled condition 
did not appear on these, the markings were mite work. These pests 
were finally checked through the workings of natural agencies. 














YELLOW STRIPE OF SUGAR-CANE. 63 











FIG. 7.—Cane-sugar stalks, showing effect of sun burn. 











64 JOURNAL OF THE DEPARTMENT OF AGRICULTURE. 


Gray blotch. 

This phenomenon consists of gray, very irregular patches (PI. 
IV) on the internodes which often coalesce to encircle and_practi- 
cally cover the entire surface. They do not pass from one internode 
to another. These areas are superficial, including only the outer- 
most layers of cells or practically the epiderm only. Certain va- 
rieties, notably B-347, are very susceptible to these markings. It 
appears probable that they are merely a result of sunburn, since 
they have been observed on stalks at the edges of fields or in posi- 
tions exposed to the direct light. Fungi and bacteria may be helpers 
or secondary agents. 


COMPARISON WITH OTHER CANE EPIDEMICS. 


As a matter of general interest it is proposed to give a_ brief 
account of certain other cane disease epidemics of the past which 
will to some extent at least throw light on the present situation. 


The Porto Rican Epidemic of 1872-80. 

There have been several other serious epidemics of cane disease 
in Porto Rico before the present one. The one entailing the greatest 
loss (estimated at $796,500) occurred between the years 1872-80, 
reaching its height about 1876. A commission of three local men 
was appointed by the Government to study the disease and in 1878 
they presented a lengthy report (1). The region infected as given 
in this publication, included the cane lands around Mayagiiez, Agua- 
dilla, Hormigueros, San German, Cabo Rojo, and to a limited extent 
some territory beyond these municipalities, both on tle north and 
south coasts. This was what constituted the fourth department of 
the Island. 

In many respects the observations of the commission corresponded 
with those noted for the present trouble. The disease spread rap- 
idly, quite irregularly, and was not checked by rivers or hills. The 
symptoms are described as follows: 

‘Los fendmenos que presagian el principio de la enfermedad son 
regularmente cierto tinte amarillento que se nota sobre los cana- 
verales, el desarrollo tardio y dificil de las canas, y una vez cose- 
chadas y molidas, la baja en cl rendimiento. Al aio siguiente, en 
las canias que nacen, al parecer buenas y lozanas, reaparece el tinte 
amarillento del primer periodo y continiian asi hasta 4 6 5 meses, 
que corresponden al desarrollo de los primeros caiutos. - - 

“‘Después continia el color verde amarillento en todas las hojas 
que acaban por secarse, primero las inferiores y sucesivamente las- 








dc 

de 
ar 
to 


di 


di 


C0 


a 














YELLOW STRIPE OF SUGAR-CANE. 65 

demas, mientras los caiutos que van saliendo permanecen cortos y 
delgados; la yema terminal o cogollo se seca a su vez, y por fin, 
arrugandose primero los canutos superiores o mas débiles y después 
toda la cana, termina ésta por secarse completamente. 

*“Canas enfermas procedentes de canaverales enfermos, sembra- 
das en terrenos sanos y distantes del foco de la enfermedad han pro- 
ducido canias sanas, y canas sanas extraidas de las mds e.xccelentes 
_canaverales, transplantadas a los que sufren o sufrieron han pro- 
ducido caias enfermas.’’ 

There were no other consistent symptoms. The occasional cases 
of internal red rot and rot of the buds were probably due to specifie 
causes: The common cane insects were studied and a decision made 
that they were not directly concerned. <A study was also made of 
weather conditions with particular reference to drouth, but it was: 
found impossible to make any correlations. All measures such as 
increased fertilization, use of lime, ashes, and a number of chemical 
poisons were without effect. The commission after frankly admitting: 
that they had been unable to find a cause advised the immediate: 
extension of planting of several hardy varieties, particularly Morada 
and Crystallina in place of the universally grown white cane (Ota- 
heite), which had shown no resistance. They also advocated the 
introduction to the Island of new varieties from other parts of the 
world. 

While in some respects this epidemic resembled the one now 
raging the perusal of the symptoms as compared with those of the 
latter does not make it seem probable that they are the same. No 
reference is made to mottling or stem cankers, but to a yellowing 
of the leaves only, followed by a drying of the bud. 

Some years later Don Manuel Fernandez Umpierre (11), admin- 
istrator of Central San Vicente, published in his work on sugar-cane 
an account of the same epidemic and his experiences in controlling 
it. According to his statements, the disease yielded to careful cul- 
tivation with particular attention to drainage, even though the very 
susceptible Otaheite was used. It is quite probable that by the time 
he took up the problem the disease had about run its course, and 
even at its height it had hardly extended as far east as San Vicente. 
Other points, such as origin of the seed used in his experiments, 
are not sufficiently clear to warrant further discussion of this paper. 

In 1895, Don Fernando Lépez Tuero, director of an experiment 
station (not the present station) published (19) as part of his work 
on sugar-cane a lengthy article on what he considered to be the 
same disease. After investigation of a number of possible factors 














66 JOURNAL OF THE DEPARTMENT OF AGRICULTURE, 


he decided that white grubs (Phyllophaga spp.) are ‘responsible, and 
proves this theory to his own satisfaction by a series of field observa- 
tions and planting tests) The present writer inclines to the belief, 
after a close perusal of Lépez’s paper that he was correct in his 
surmise that white grubs were responsible for the death of cane 
over large areas. His description at least does not suggest the mot- 
tling disease, but is fairly exact for white grub injury. 


Other Porto Rican cane disease epidemics. 

This, so far as known, includes all recorded cane disease epi- 
demics of any importance up to 1907. About this year trouble was 
again experienced with the Otaheite variety, this time in the Na- 
guabo district. The disease here was very clearly a deterioration 
of a long planted variety brought about by rind (Melanconium 
sacchari) and root disease (Marasmius, Odontia), and other un- 
favorable conditions. The symptoms were characteristic in all re- 
spects for these two maladies, and no signs of mottling were seen 
at any time. The situation was overcome by the introduction of 
new varieties to replace the white (Otaheite). 

It thus appears that although Porto Rico has suffered from severe 
epidemics of cane disease in the past, the present peculiar type has 
not occurred heretofore. Not only has the literature failed to bring 
out anything suggestive of it, but conversations with old residents 
who had personal knowledge of the sick cane of 1872-78 does not 
make it all probable that the two were the same, at least in so far 
as visual symptoms are concerned. 


Serious cane disease in other cane regions. 
Practically every sugar-cane growing country in the world has 
suffered at one time or another heavy loss from disease, deteriora- 
tion, or a combination of the two. For example, Porto Rico 1872-78, 
Mauritius 1841, and again in 1872, Java 1882, Antigua and others 
of the British West Indies 1895-99. Some of these visitations have 
been due to unknown causes, others have been designated as rind 
disease, sereh, or root disease. As a matter of fact most of them 
come under the head of deterioration. In a considerable number of 
these epidemics the Otaheite or Bourbon cane has been involved. 
One of the most striking instances of this kind was the running 
out of this variety over a number of years (1895-99) in Barbados, 
Antigua, and others of the British West Indies. This has always 
been ascribed to the rind disease, and was satisfactorily checked by 
the substitution of new and more resistant varieties, a measure 
which has served to overcome the various epidemics as well. 








— tet, CA ~*~. 


=" 

















YELLOW STRIPE OF SUGAR-CANE. 67 

During recent years the Lahaina cane of Hawaii (probably the 
same as the Otaheite) has been failing in certain districts, giving 
rise to what is known as the ‘‘Lahaina trouble.’’ Various agencies 
have at one time or another been held responsible, top-rot, stellate 
erystal fungus, poor drainage, senility, and others but the actual 
cause is still obscure. New varieties and possible changes in cultiva- 
tion and fertilization seem to be the control measures now being 
tried. 

It is apparent that the system which had universally prevailed 
in all cane countries, at least until serious diseases have appeared, 
of growing one variety to the practical exclusion of all others, has 
resulted in all of them, though at different times, in a deterioration 
of the plants so decided as to assume the proportions of an epidemic. 
In each instance secondary factors, such as rind disease and other 
fungi, have appeared, so that the visual symptoms have varied over 
a considerable range, though the underlying causes were the same. 


=) 


Rind disease. : 

Principally because of resemblances to the ‘‘rind’’ disease epi- 
demic of the British West Indies particular attention was given to 
a search for this disease. The drying and shrinking of the stalks 
from the top downward with consequent death of the leaves and the 
final production of the innumerable conidial masses was conspic- 
uously absent, much less being found in mottled fields than occurred 
in normal fields elsewhere. Not even in abandoned third phase 
fields could Melanconium be found, except in isolated cases. Near 
Camuy a field of Rayada of nearly fifty acres was discovered which 
it had not been possible to cut for the mill, and which was being 
left until the following season. Not a sign of mottling was present, 
but it was fast approaching total loss due to rind disease. 

No evidence has been obtained to bear out the theory that JJelan- 
conium may be present in stalks which appear normal. 


Gumming. 

The question will arise in the minds of many as to whether or 
not mottling is connected with gumming disease (Bacterium vascu- 
larum) of sugar-cane, if not in fact that identical disease. A sum- 
mary of the symptoms of this latter disease, practically none of 
which apply to mottling, should clear up this ponit. Quoting Dr. 
Erwin F. Smith (25), ‘‘The most conspicuous signs of this disease 
(gumming) are dwarfing, striping of the leaves, drying of the tops, 
decay of the heart (terminal bud), and the appearance of a yellow 

















68 JOURNAL OF T'HE DEPARTMENT OF AGRICULTURE. ' 


slime or gum in the bundles of the stems and leaves. Many of the 
bundles are also stained red.’’ 


CONTROL. 


Particular attention naturally has been given to the very im. 
portant subject of control, and a number of popular accounts (35, 
34) of the disease have dealt largely with this topic. It has been 
necessary to modify from time to time the measures recommended 
as further data on the course and nature of mottling became avail- 
able, but with the definite knowledge now at hand it is possible to 
outline a satisfactory system for control. 

It will be noted that it is control measures and not remedies or 
a ‘‘eure’’ that it is proposed to discuss. It has at all times been 
apparent to those working on the problem that a remedy was out 
of the question, although this has been the persistent demand of 
many of the cane growers. Much time and effort have been ex- 
pended in attempting to combat theories based on such views and 
to make clear the fact that a plant once it is attacked remains so, 
and that there is but one thing to be done with it—destroy it to 
prevent spread of infection. 

Several instances have been reported of individuals who were 
offering remedies for sale. It was never possible to obtain samples 
of these products nor definite information concerning them nor does 
it appear that any results were obtained from their use, if indeed 
they were ever used. 

A suggestion was made in last year’s report that where the per- 
centage was not too high, diseased stools should be dug out and 
destroyed. At the time the idea in mind for the most part was to 
prevent any chance of diseased material being taken for seed. When, 
however, the infectious nature of the disease became so clearly evi- 
dent, an experiment started for studying the spread of the disease 
(already described) was changed to one for eradication. The chart 
(Fig. 2) will show the number of stools dug from the field up to 
November first. Since that time several additional scoutings have 
been made and a considerable number of newly diseased stools re- 
moved. In the beginning of this work mottled stalks only were 
removed in order to ascertain whether the disease would appear 
later in other portions of the same stool. This was what actually 
occurred in all cases, so that it can be stated that in attempting 
eradication work entire stools should be removed no matter now 
few stalks actually show mottling. This partial removal complicated 
the task of eradicating the disease in the field in question, as did 














he 











YELLOW STRIPE OF SUGAR-CANE. 69 
the fact that it had been permitted to spread unchecked over one 
full season However, results in the main have been satisfactory. 

Some attempts on a field scale have been made to eradicate the 
disease by digging out of affected stools, but the difficulty of securing 
the united or continuous effort necessary to insure the success of an 
undertaking of this nature has made its thorough carrying out almost 
impossible. Apparently only the prospect of complete ruin can 
force this action. 

One specific case has been under observation for the past two 
seasons where work of this kind has been in progress. This is a 
finca of about 500 acres situated in a badly infected district. In 
addition to digging out diseased stools at the time the cane is about 
two feet high, the best of culture including seed selection, liming, 
fertilization, deep plowing, and similar measures have been prac- 
ticed. The white cane has been eliminated and the hardier Rayada 
and Cavengerie canes are being used. The fields composing this 
tract are contiguous on two sides to other cane fields which have 
been given ordinary care only and are badly diseased, so that the 
whole constitutes a severe test of the eradication proposition. Re- 
sults have been very favorable and form an object lesson of what 
could be accomplished by united action. 

The value of seed selection with elimination of seed from diseased 
stalks should not need more than passing mention because of its 
already demonstrated relation to control. All experiments and field 
observations prove absolutely that diseased cane always results from 
diseased seed, hence the vital necessity of eliminating it. This has 
been ignored by many of the growers or at least not thoroughly 
attended to. 

There is of course a difficutly experienced at this point because 
of the fact that seed pieces may be diseased without giving outward 
signs once the leaves are removed. Cankered pieces could of course 
be readily eliminated. This problem brings up again the advisa- 
bility of cutting out mottled stools before the cane reaches any great 
height. Some infection will doubtless occur after the cane has closed 
in and is of such a height as to make it inadvisable to scout the 
fields further, but the amount would be reduced to a minimum. 

The ultimate solution of the problem lies in the finding of im- 
mune or at least strongly resistant varieties as is the case with so 
many tropical plant disease problems. Several of the seedlings pro- 
duced by the Insular Experiment Station and tried out in infected 





1The plan of eradication proposed in Circular 14 of the Insular Experiment Station, 
Rio Piedras, P. R., has been widely adopted on this Island.—Ep1Tor. 














70 JOURNAL OF THE DEPARTMENT OF AGRICULTURE. 

areas, give promise but certain results can only be secured by trials 
carried out over a series of years. Since a disease similar if not 
identical to the mottling, occurs in Java and Hawaii and is there 
kept in check by resistant varieties it is not at all improbable that 
some of these will prove of value in Porto Rico. Lyon in this con- 
nection suggests the striped Mexican (which seems to be the same 
as the striped or Rayada of Porto Rico), D-1135, and Badilla, all 
of which are reported ‘‘as very resistant to yellow striping.’’ 

Even though it has been shown that cultural factors are not 
directly concerned with the presence or absence of mottling or its 
relative virulence, it must not be lost sight of that these are still 
matters of vital importance to the cane growers, and should be given 
constant attention since other diseases are always present in Porto 
Rican fields, and may easily cause serious damage if neglected. Im- 
proved cultural methods will give greatly increased yields in spite 
of the presence of the disease and so help to overcome the losses due 
to its occurrence. 

The measures recommended then for control may be briefly 
summed up as follows: 

Seed should not be taken from diseased stools. Certain fields 
should be assigned to seed production and a determined effort made 
to clear of mottling by digging out any stools which become infected. 

Seriously diseased fields or those where the returns will be so 
reduced by the presence of the disease as not to cover expenses 
should be plowed up. Because of the great number of volunteer 
diseased shoots that would appear, replanting immediately should 
be done only in case of necessity, and then only after very careful 
preparation of the soil. 

Where the amount of disease present is not over a small per 
cent of the total number of stools, an attempt should be made to 
eradicate the disease by digging out diseased stools, using care to 
get out all the rhizome or underground portion of the plants. Such 
holes can be replanted since there is no evidence that infection is 
spread through the soil. The dividing line between fields to be 
ploughed up and those to be ‘‘rogued’’ must be determined by each 
individual grower, since it involves the economic side of the situation. 

In planting the hardier canes should be used and whenever pos- 
sible new varieties should be given a trial. 


SUMMARY. 


A serious epidemic of cane disease has been raging in Porto 
Rico for several years and continues unabated. 








YELLOW STRIPE OF SUGAR-CANE, ql 


While various names have been applied to it, mottling disease 
is the preferred name. 

The disease first appeared in the northwestern section of the 
Island (Arecibo-Aguadilla) and has spread rapidly eastward, until 
only a portion of the east and southeast coast regions remain unin- 
fected. Indications point to continued progress of the disease. Up- 
land fields have as a rule been the most severely attacked. 

Losses to date are estimated at $2,500,000. Losses are produced 
by a reduction in tonnage. Difficulty is often experienced in hand- 
ling the juice of diseased canes in the mill. 

Observations and experimental plots demonstrate that the dis- 
ease spreads by other means than infected seed pieces. 

The mottling disease has been found on several varieties in Santo 
Domingo where is was not epidemic. One infection area has been 
reported from St. Croix. 

The white (Blanca) or Otaheite was first seriously attacked, but 
in succeeding seasons the Rayada and other native types have sue- 
cumbed. The numerous foreign varieties, mostly seedlings, vary 
greatly in their behavior, certain ones being very susceptible, while 
others give promise of proving satisfactorily resistant. Some of the 
station seedlings are promising. 

The disease is characterized by a mottling of the leaves, followed 
in advanced stages by a stunting of the entire stool and the presence 
of gray, sunken lesions on the stalks. The appearance of the mot- 
tling varies greatly with the variety infected. Approximately a 
three-year course is followed, the disease becoming more pronounced 
with each succeeding ratoon, and ultimately causing death of the 
affected stools. No other hosts have been found. 

A field to field survey has confirmed the opinion held that nature 
of the soil, years in cane, method of preparing the land, drainage, 
and other cultural factors have no direct relation. 

Field and plant house observations and experiments demonstrated 
that fertilizers, liming, seed treatment, manner of disposing of the 
trash, soils, moisture content of soil, and all similar points have no 
direct influence. There is an accumulative effect in successive ratoon 
crops. 

It has not been possible to transmit the disease artificially. 

Chemical tests of the juice do not show any abnormal glucose 
ration or any constant difference between the juice or normal and 
diseased canes. 

Fungi and bacteria are not associated in any way as causal 
agents, either on the leaves or stalks. The cankers are a result of 











72 JOURNAL OF THE DEPARTMENT OF AGRICULTURE. 

the general weakening of the plant, and are not primarily caused 
by fungi, which may, however, invade them later on in their develop- 
ment. 

Planting tests of stalks showing leaves mottled in part only 
demonstrate that the infectious principle is present in all parts of 
diseased plants. 

The disease is transmitted by means of diseased seed pieces, but 
has also some other means not yet apparent. It does not persist 
in the soil and infection is aerial. Certain insects are suspected as 
carriers. 

The disease is considered to be an infectious chlorosis due to « 
virus or ultramicroscopic organism. The degeneration theory pre- 
viously advanced is completely abandoned. 

Lyon of Hawaii suggests that the yellow striping disease of Java 
and Hawaii is the same. There are many points of similarity, but 
lack of literature and authentic material of the vellow striping makes 
a final conclusion undesirable at this point. 

Sereh is an infectious cane disease of Java which has been epi- 
demic at times. It resembles mottling in some respects but is suf- 
ficiently distinct. The causes of the two diseases are thought to be 
of the same nature. 

A comparison of symptoms, manner of transmission causes, and 
related points is made between mottling and the curly-top of beet, 
tobacco mosaic, spinach blight, peach yellows, cucumber mosaic, po- 
tato mosaic and other abnormalities of potatoes, all of which it is 
thought are due to similar causes, 7. ¢., ultramicroscopie organisms. 

There are a number of diseases or abnormalities of cane which 
have been or might easily be confused with mottling. Deterioration 
is a phenomenon due to long continued cultivation of one variety, 
to poor cultivation, to unfavorable weather or other non-parasitic 
conditions. It is marked by a yellowing of the leaves and stunting 
of the stools. 

There is a form of root disease due to the action of parasitic 
fungi which have not yet been clearly differentiated. Chlorosis is 
a yellowing or whitening of the leaves of entire stools in limited 
areas due to inability of the plants to assimilate sufficient iron in 
the presence of an excess of lime in the soil. Yellow spotting is 
characterized by spots on the leaves resembling those of mottling 
but more yellow in color. The condition is due to lack of cultiva- 
tion or drouth. 

Certain varieties of cane are subject to long white stripes on 
the leaves which are of the nature of chimeras. Under green-house 











YELLOW STRIPE OF SUGAR-CANE. 73 


conditions mites produced markings on the leaves almost indistin- 
guishable from those of mottling. 

Sun burning and possibly surface-growing fungi produce gray 
blotches on exposed stalks. 

A very serious epidemic of cane disease occurred in Porto Rico in 
1872-80 and was studied by a royal commission without the cause 
being ascertained. In some respects it resembled the mottling but 
cannot be considered to have been that disease. It was controlled 
by natural factors and the use of resistant varieties. A later phase 
of the same situation was shown to be due to white grub attacks. 

There have been minor epidemics, and one in particular of rind 
disease, but it has not been possible to trace any earlier occurrence 
of mottling, indicating that it is a recent introduction. 

There have been serious outbreaks of cane disease in practically 
all other cane-growing regions of the world, including Java, Mau- 
ritius, and the West Indies. The mottling disease has no connection 
with either the rind (Melanconium) or gumming (Bacterium vas- 
cularum) diseases. 

Control lies in the use of disease-free seed, and the elimination 
of diseased cane either by plowing badly attacked fields or by dig- 
ging out diseased stools. United action on the part of all cane 
growers is necessary. The more resistant varieties should be used 
to the exclusion of the very susceptible types, and continued search 
made for varieties still more resistant or even immune. 


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1914. Mosaic Disease of Tobacco. U. S. Dep’t Agric. 
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1918. Instrueciones para la Eradicacién de la Enfermedad 

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(12) Girz, P. L. 

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