'SESSlON-';;'PATl:IOLOGIOAL AND E~rTOMoltOGI(1Ar. $ElOTfONiS,

Mr. O. E.Pemberton, Ohairman.

paper on the" Importance of the Virus Diseases of )Sugar Cane,"Brandes and .T. Matz, was read by the authors. IIIi introducing the

r Dr. Brandes stated that it was a retrospective survey of the work done'{rus diseases over the last 15-20 years and was nota definite contribution(Ow facts. In the paper they had assumed that sereh and dwarf diseases

virus diseases. In commenting on the question of virus strains hehed that there were now recognised 59 strains of tobacco mosaic,

Paper.

Importance of the Virus Diseases of Sugar Caneby

E. W. ~RANDES, P'r'i/ncipal Pathologist in Charge,and JULIUSMATZ, Pathologist,i· ,

ion of Sngar Plant Investigat{01~'s,Bureau. of Plani Industry, United StatesDepartment; of Agriculture.

General and TheoreticaL Oonsiderations.

Without question, the virus diseases of sugar cane,' as a group, takeplace at present among the disease hazards of this staple crop plant,

ough other diseases, especially those caused by soil inhabiting organisms,attain to this unenviable distinction later if they do 'not prove amenable

easures of control, which, in the case of most virus diseases, have been wellanced. The economic importance of cane virus diseases" belting the globehey do, would be difficult to state in terms of capital loss and reducedme. As a somewhat inadequate measuring stick, the losses caused by onlyof, them, mosaic,in the 'United States during the period 1919"1929, has beenated at more than $100,000,000. The United, States supplies its own

s of sugar from cane very insufficiently, the yearly output being enough tod the population for only three weeks. 'The toll taken by mosaic in thistively unimportant sugar industry will give some conception of the poten­hy for damage to sugar cane the world over by these diseases. In com­ing the different virus diseases" from the standpoint of significance tomercial cane culture it must be held in mind that they are here consideredveral aspects, historically as well as currently, and to give them a definiteing would, be confusing. It will be sufficient, therefore, to indicate in a

'.eral way (1), the extent of injury to individual plants caused by the differentUs diseases; (2) the areas where they are known to occur and the coneentra-

of diseased plants in those areas; (3) the manner and velocity of spread

* Several of phe diseases reviewed in this paper are, by the majority of plant patholo­who have experimented on them,provisionally classed as virus diseases because of one

ore points of similarity in common with such diseases, but without definite proof thatare caused by filterable viruses.

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tohe~lthyplants, ~nd (4) the probable efficacy of control measures. In somediseases thesepoints,have yielded to study, and knowledge is fairly complete.In other cases efforts of long duration have not' been very productive, and instill' other cases the time has been too short to advance knowledge to any extent.These features considered with certain other incidental ones not common toall virus diseases of cane, form a basis for evaluation which will enable theattentive observer to assign the individual diseases to positions .of .relativeimportance.

As some aspects of the virus diseases seem to connote a relationshipof the whole group, these aspects may be considered first, followed by brief,separate considerations of the individual diseases.

The general conception is that the virus diseases are new and one iscompelled to acknowledge that they are new in the sense that anything approach­ing complete factual acquaintance with them is of recent date. The question,of whether these are new manifestations in sugar cane possesses for us morethan philosophical interest because the hope that they may be held in checkby naturai means, i.e., by, some protective device or principle' in the plant,would seem to be more justified if there is reason to believe that sugarcanehas been continuously or..intermittently exposed to' infection for' thousands ofyears and survived it, rather than if the evidence points to very recent exposure.If the virus diseases are ancient there must be some explanation for belatedrecognition of them. Why did identification of the virus diseases as ,maladieslag behind recognition of the fungous and bacterial diseases, or disturbancescaused by environmental factors Or deficient or unbalanced nutrition ~ In thecase of most other troubles cause and effect were more easily correlated becauseof the presence of conspicuous lesions associated with foreign organisms, whichcould be artificially cultured, or the presence of other signs traditionally asso­ciated with soil, water or weather relationships. With a few exceptions therewas no obvious relationship of the plant infected 'with a virus and anythingthat was possible to visualize or with any condition that was tangible .or con­ceivable until the trail was blazed by the classic work on tobacco. The investi­gation of tobacco mosaic is, in contrast with studies and advances in knowledgeof the orthodox forms of maladies, of such recent date that it comes within thespan of life of many of us who do not admit to more than middle age.with the guiding light ofthebrilliant work on tobacco mosaic, which was quicklyseized upon by animal pathologists as well as some plant pathologists to elucidateformerly obscure diseases, many years elapsed before there was any intimationthat viruses were concerned with sugar-cane abnormalities. Twenty-severipassed by before anything like proof that would stand scrutiny wasto identify the" matizado" or "gelestrepenziekte" with a filterable virus.explanation is many-sided but not .difficult, Clouded and burdened by prejudices:we resist ihcideathatis' unfamiliar. If, when it is presented first to view;,'the riewly forged chain requires an additional .link (in this case, clear evidence:of infectiousness and its method of operation) we are Ied to accept irilieuthe discontinuous· sequence of strong links,varioustraditional but

"

"·,-"i·"'·

'" 'Mutatiop.," 'tdegeneration,' depleted .soils, ulllfavOllIrllble,v-vea,tllJ3r'explanations were at different'times mvokad

"ic. It is not hard to understand either the belated recordmg(distinctive manifestation in cane, or the failure to properly Clfli3S:Lfy

;: The virus diseases are most likely not new and the one that We are~concerp.edwithmay have caused many an old Papuansorcererto apostro­il, fora consideration, the spirit of the rain on behalf, of horticultural clients

ago.

This leads naturally to a second group consideration, of the virus diseasesgar cane. Where did they originate and has this question any implication'

he evaluation of the diseases asa continuing threat to the industry. Theiraphical .points where they were first observed and recorded should ben into account, but in generaf these are not very illuminating because of" of evidence tending to link them with diseases of other plants locally and, because of insufficient evidence on the course of migrations of the canet to those points. It is the opinion of many that sugar cane itself originated, elanesiaand adjacent .south-eastern Asia; therefore,an examination ofe areas, particularly the sections where no great interference with natural

uditions has taken place, might throw light on th~place of origin of thefllses. If the diseases are found on cane in aregion where cane has not beentroduced by man and -natural conditions are relatively undisturbed, the weightevidence would lean toward that region as the place of origin of the disease.

'Mr such places have been examined with special attention to sugar cane, anddiseases but the great island of New Guinea is an exception, severalexpe­

ions having made cane a special object of inquiry. 'His reasonable to supposeit no sugarcane has been taken to New Guinea and planted in recent years,l.'haps not for thousands of years. There would be no point in such an intro­etion because of the abundance of sugar cane crudely cultivated by the natives;d the profusion of wild and transition 'forms, sufficiently explaining' thesence of the cultivated ones.' The significant fact is that two of the virus:ases of cane, mosaic and Fiji disease, have been found in New Guinea.

ither disease is conspicuous or abundant there but, assuming one-way trafficsugar cane outward from New Guinea and not inward, presence of theease in any amount would seem to establish that this island is a place-of

'gin of the diseases mentioned. Together with the records tracing the out­eaks of Fiji disease in Fiji, Australia and the Philippines to cane originally,om New Guinea, the evidence is enough to incriminate New Guinea beyond,x'easollable doubt. It imiy be of interest to record that a third virus disease,'eak, is, under suspicion of being an inhabitant of New Guinea.

'l'wo and possibly three-of the virus diseases of sugar cane are in ~e)¥'

,,)nea and the possibility that others are also there is not precluded. OPl)oi'­'flilitieR for observation by trained investigators have been limited and failureQ'seeother virus .diseases if present may be excusable, because the onesrecorded~de:finitely known to be of rare occurrence.

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Serehand chlorotic ,streak are known in Java, where sugar .cane mayhave independently originated. Although. the problem of whence sugar canesprang is not before us, the accessory question, place of origin ,of the virtu;diseases, cannot very well be divorced from it and we venture to say that thereis no reason to doubt independent development of the cultivated cane varietiesfrom related wild forms throughout practically the whole area represented bythe range of the latter. It seems, however, that the more slender cultivatedvarieties are found at the fringes of the area, in northern India, southern Chinaand Formosa, and the thicker-stalked cultivated varieties are nearer the centre.~This corresponds to the ranges of the thin and thick stalked wild formsalthough, of course, the thin wild canes co-exist with the more robust ones atthe' centre. The latter, similar to S. robusiwm; are known only in New Guineaand the Celebes. Wild forms intermediate in size, but assigned to the speciesS. eponiomeum. are found in the Malay peninsula and Sumatra. It is postu­lated, based on these gross morphological characters, but also in a measureconfirmed by cytological evidence, that in the main the cultivated examplesof S. barberi and S. sinense are derived from the numerous wild forms of S.spontanet~m and that the cultivated examples of the so-called S. offiGinartmn,*descended from S. robuetum. or, since they freely cross, many of them fromboth S. robusium» and S. spontaneum.

From the area where the wild progenitors of cane are found movementor migration of cultivated sugarcane has been exclusively centrifugal and,withthe exception of insignificant amounts in recent years, 'continues to. be directedoutward. The virus maladies, mosaic, Fiji disease, chlorotic streak, serehand probably streak, are all found within this area. The insignificant backwashof sugar .eane into the region, represented by a few recent, well recorded.importations of varieties by experiment stations, does not account for thepresence there of these diseases and the logical assumption is that they alloriginated within: the area. The presence of these diseases' in all other areascan, with a few exceptions (notably streak in South Africa) be definitelylinked 'with the radiating movement of sugar cane from this centre. In manyinstances the presence of the diseases in countries where cane is exotic canbe traced to particular importations from the countries where it is indigenous.To cite a few examples, sereh in Formosa can be traced to Java; Fijiin Fiji,and Australia to New Guinea; chlorotic streak in Puerto Rico to Javamosaic in Argentina to Java. The examples could be multiplied but are already"well known to 'cane pathologists. A fact that compels attention is thatin its earlier migrations, including that carried by those incomparable marmers.,the Polynesians, seems to have been singularly free from these diseases,diseases following much later. In the case of what may have been the firslong journeys, those to the widely separated tiny peaks of land in the souther

* The thick-stalked, "noble" varieties of sugar cane are usually assIgned to thi;species, said to have 40 chromosomes, which happens to be the number found in S.robustu'However (in our experienee), 40 chromosomes are f'ound in relatively few of the 'varieties, .most of which have larger numbers.

the diseases have in some cases not yetpursuit of .the cane. The inevitable conclusion

e time when intensive cultivation of sugar cane developedindustry the diseases were present there but disease incidence was not

at and this is borne out QY the previously mentioned scarcity of mosaicIji disease in New Guinea. An explanation for the extremely rare occur­of the diseases in Nsw Guinea and their assumed rare occurrence inst over the whole area is to be found partly in the wide separation of

cry small cultivated plantings, the effective barriers of jungle between.the constant feuds between tribes and villages which limited intercom­ation to infrequent raids, and partly in the demonstrated ability of

~to recover from at least one disease, mosaic. In another paper [5] it has. suggested that .mosaie is not a naturally occurring disease in cane butrids upon occasional and transitory infection from some other source,ably a wild grass associated with cane where it is indigenous. Nothing canid as to possibility of similar relationships of the other virus diseases.

'her they represent primitive, exclusive associations of cane and virus'ot, it is almost certain that cane has been exposed to. infection for a verytime and has survived it measurably well. .

This should encourage the hope that within the genus Saccharum is to beinherent resistance to the virus diseases and that is precisely what has

€lady been demonstrated in varying degree for several of .the diseases,uding mosaic, sereh, Fiji disease, and apparently chlorotic streak.

In contrast, the expectation of resistance if tlie evidence pointed to a.erent geographic origin of host and virus would be much less. If, as has

suggested, the viruses were peculiar to grasses or other plants in areasere the most striking epiphytoties have occurred,places remote from the ho~e

'sugar cane, the chance of quickly locating resistant forms would be diminishedd problems would be presented as serious as curly-top in' sugar beets or

;'Hows in peaches. These plants, introduced to America encountered there'rus diseases entirely new to them and progress in finding even slightlysistant beets has been slow and laborious, while dependence on other expensive'

.ethods of controlling yellows has been forced upon the growers. A feelingr helplessness and resignation attaches to many of the examples of sudden'.• pact of new and unaccustomed diseases with plants, animals and even man,•d it becomes important to give what assurance is possible that in the groupt virus diseases of cane we are not dealing with such cases. Because observa­ions and records are fragmentary much that has been said regarding thentiquity and place of origin of the diseases is admittedly based on reasonablessumption, together with patchwork evidence. However, most plant patholo­

gists will agree that with no evidence at all the main thesis is a logical.supposition, in keeping with the majority of better documented cases and the~ccessory postulations in respect to the effect of such relationships represent;the rule rather than the exceptions.

,. ' , ,",

Ocean, the diseases have in some cases not yet theireSS pursuit'. of .' the cane. The is that

e the time when intensive cultivation of sugar cane developed in the cradlee industry the diseases were present there but disease incidence was noteat and this is borne out by the previously mentioned scarcity of mosaic

'Fiji disease in New Guinea, An explanation for the extremely rare occur­e of the diseases in New Guinea and their assumed rare occurrence inpast over the whole area is to be found partly in the wide separation of'very small cultivated plantings, the effective barriers of jungle between

the constant feuds between tribes and villages which limited intercom-,ication to infrequent raids, and partly in the demonstrated ability ofto recover from at least one disease, mosaic.. In another paper [5] it hassuggested that mosaic is not a naturally occurring disease in cane but

nds upon occasional and transitory infection from some other source,.' ably a wild grass associated with cane where it is indigenous. Nothing can

isaid as to possibility of similar relationships of the other virus diseases.;ether they represent primitive, exclusive associations of Cane and virus'

ot, it is almost certain that cane has been exposed to infection fora verytime and has survived it measurably well. .

This should encourage the hope that within the genus Saccharum is to bend inherent resistance to the virus diseases and that is precisely what has~ady been demonstrated in varying degree for several of .the diseases,uding mosaic, sereh, Fiji disease, and apparently chlorotic streak.

In contrast, the expectation of resistance if tlie evidence pointed to aerent geographic origin of host and virus would' be much less. If, as hashsuggested, the viruses were peculiar to grasses or other plants in areas

'ere the most striking epiphytotics have occurred, places remote from the home~ugar cane, the chance of quickly locating resistant forms would be diminished~'•• problems would be presented as serious as curly-top in' sugar beets orlows in peaches. These plants, introduced to America encountered therers diseases entirely new to them and progress in' finding even slightlyfstsntbeets has been slow and laborious, while dependence on other expensive'thods of controlling yellows has been forced upon the growers. A feeling.. helplessness and resignation attaches to many of the examples of suddenpact of new and unaccustomed diseases with plants, animals and even man,

it becomes important to give what assurance is' possible that in the group.virus diseases of cane we are not dealing with such cases. Because observa-ns and records are fragmentary much that has been said regarding thetiquity and place of origin of the diseases is admittedly based on reasonableumption, together with patchwork evidence. However, most plant patholo­ts will agree that with no evidence at all the main thesis is a logicalposition, in keeping with the majority of better documented cases and the

,cessory postulations in respect to the effect of such relationships represent~ rule rather than the exceptions.

I'ilIi

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'I'hedisease ltiiown.as dwarf is the latest addition to the group of virusmaladies, and because so little is known' of it no fruitful consideration ofthese points is possible. 'It is fortunate that following the impetus given bythe first advances' in knowledge of the biology of mosaic" which definitelyclassified it as a virus disease 15 years ago, investigations of similar diseasesin widely separated countries have been in unusually competent hands and itmay be confidently expected that new light will quickly be thrown on diseasesrecently admitted' to the circle of virus diseases and continued progress willbe made on the old ones.

Mention has been made of the fact that control measures for some of thevirus diseases have been . well advanced but, with the possible exception ofsereh, it cannot be said that any of the diseases have become negligible threatsto the industry as a result of progress in controlling them. In general, thevirus diseases are perpetuated by vegetative propagationof'affected plants,and this suggested roguing as the most obvious and consequently the earliestused method of control. Unusually large amounts of disease sometimes presentin mill fields contra-indicate roguing, but in many cases the method isjustifiable. Where it can be used, a device of\ more utility is roguing of seedcane fields, thus insuring practically disease-free planting material. Anymethod of extermination applied directly to the diseased plants in mill fieldsmust be used with due consideration of the chance of net gain, which may beexpected due to elimination of all or part of the sources of virus by destructionof injured but valuable "millable plants,and this, of course, involves predic­tionof the amount of secondary spread. Because the rate and amount ofsecondary spread are often unpredictable; good judgment and an understandingof the essential biological principles must dictate the course of action. Effortsin this direction, however carefully performed, almost never result in com­plete eradication because the diseases cannot be detected in the "incuba,tionperiod." There remain always a few infected. plants, which may eventually

-result in a surge .of spread that would nullify and make unprofitable theexpenditures in roguing. The, use of roguing" is. obviously indicated whereareas are newly invaded and the numbers of infected plants are small, and inareas where epiphytotic conditions are temporarily halted, offering the chanceof effective work in reducing 'the danger' of massive spread, if subsequentlyconditions become favourable for rapid secondary infection. During a ful­minating epiphytotic it is practically useless to attempt control by roguing.Records over periods of 10 to 20 .years indicate that in the case of mosaic, atleast, certain regions are singularly free from serious epiphytotics and otherregions are subject to periodic outbreaks correlated with the seasons, while stillothers are observed to have outbreaks at irregular intervals. These phenomenaare certainly correlated with conditions affecting the wild hosts and the insect

The insectvectors appear.to be' indispensable agents of virus transmissionnatural conditions in',. the '. cases of mosaic,', streak, and Fiji disease" and

ctsmay, be involved in the transmissionofsereh, chlorotic streak, and '. dwarf.virus in no case has been proved to existin theair,in water or in the

'but so, far as known resides' only in-the ' infected living '" plants and in,in speciesofinsects thathave~fedupon them. This suggests the possibilityontrol by interposingSOlnethingbet",eentheplant and insect, distasteful'oisonous to the latter or elimination of the insect as a factor by some'l' means. 'The manifestadvantageoL destruction or control of the'ct constituting as it does the, only known vehicle between infected and",." '. .:. - ,,':,,' -' ".' '-, "

lthy plants, has stimulated thought on the subject 'but, thus faras not beep fruitful. ,The insects are true bugs with sucking mouthpartstherefore stom~ch poisonsspraye'd on. the cane plants would not kill them,

11 if the problemsofeffective coverag(jandeconomicalapplicationcould beed. No progress has been madeoncontrol of the 'insectshythe use ofsites or by other biological control measures; , Although it is almost certain

(we have in the insect vector the exclusive "bottleneck, " it has, defied'rts to insert the cork and. some method, until 'now 'occult, must come intow if we a:reto take advantage of what at first sight seemed, to he, an,prtunity to stop th(lfloW' of virus to new plants. '

Yi, Natural" ~ecoverr" of sugar .eane and other plants infected with mosaic~sbeen reported in Cuba, Hawaii, theUnited States,. and other countries. In'me cases, the, evidence seems to indicate actual throwing off, of the virusjudged bytheperforinance of~aneplantsarisingfrom the eyes of' formerly~eased stalks,." Different eyes from such stalks may give rise to healthy or~asednewplants ,and in the limited instances reported there seems to

'little if any relation of recovered and diseased buds in their positions on'. stalk. 'In, other words.. considering a •single. stalk, the recovered, portionsy be discontinuous 'or, i~terruptea,withportions intervening that,give

to diseased plants. What appears to be akin to this phenomenon hasn reportedinsereh and chlorotic, streak. .: In the latter disease cuttings

Om diaeased.plantssomebimes give rise to apparently healthy plants. Althoughbt definit(llyproved the systemic character 'of thevirusdiseases-rs assumed,Om evidence_ of the presence of virus, in many parts and fromabnormalo~

'thological condition of the vascular system generally; therefore all these, ses may represent recovery. In addition to 'the, examples of individual:EJcoverywe have, seen mass reyoVEiry from mosaic where~he plallts oLentire~ids definitelyknowu, to have been one hundred per cent. affected later,ecame, to all appearances, one hundred per cent. healthy and remained tao

~ -' , , , ' ' , ,

for,s~vp,rill

suchhas been observed only in \I~~"a,"ll Y~HV"·Y~ --c­

that both innate characteristics of the plants and conditions of the environ-ment are involved in recovery and possibly operate in unisonto bring it about.It is well known that in sereh some condition of the environment in highaltitudes and in the higher latitudes suppresses the disease, but whether it actsdirectly on an infective principle,supposed to be associated, withsereh, orindirectly on it by some change in the physiological processes of the plant

has not been demonstrated.If it may be permitted to indulge in more speculation, the observed

recovery and all phenomena associated with it is not inconsistent with a theorypostulating the existence of some protective principle in the plant which is,present in different amounts in the same variety according to changiIlg eon­ditions of the environment, and in a larger measure the quantity of the protectiveprinciple varies in the different varieties. This protective substance orparalyzer is generated at the growing tip of the cane stalk and, dependi~g onits activity at any given time, the eyes and nodes, developing in rapid succes­sion, are endowed with the virus and a surplus of the paralyzer or the virusand a deficiency of the paralyzer. If, as has been suggested, the virus islocated in the phloem, the downward course of the associated virus and paralyzerwould account' for the discontinuous or interrupted recovery of the series ofeyes on an individual stalk. In other words, at any given time, these downwardpulsations of substances in conflict would be reflected in the disease-carryingcondition of the eyes at that time, as demonstrated by cutting the stalkplanting the eyes individually. Applying the same hypothesis to all' obsl>"'~TI>(lphenomena of infection, recovery, resistance, and immunity it is seentothe virtue of general applicability, but the difficulty comes in proving it."

Natural recovery seems in some ways related to natural resistanceimmunity and this brings us to a consideration of the most satisfactory measureof control, the utilization of the races of sugar cane having some measure of 31resistance to the virus diseases even under conditions that seem to favour the ,$diseases. The question presents too many aspects to be treated exhaustively~in a short summary such as this, but a few points may be advantageously t~considered. There is no doubt that resistant varieties, if they meet the numerous:!;other commercial requirements, constitute the ultimate solution of these prob-,(1lems as they eliminate special field operations which represent items of expense~and, therefore, reduce costs of production. It is possible that in the course'lof time, with the developn;.ent of more perfectly adapted resistant varieties,'i~

* In 1934 in an attempt to test the relation of diseased and recovered eyes and the ($presence or absence of active virus in all intervening internodes, cell sap was extracted,'(W

, individually from nearly 30.0 internodes of supposedly "recovery" cane ,of P.O.J. 213':11,representing 20 complete stalks. The eyes were planted and the. sap was' used to inoculat~;~1,500 test plants, but the amount of. recovery proved so disappointingly low that it was not,.,)',:

possible to reach anycone1uSion.;!~

unsafe to predictent on and. mosaic indicating that distinct strains of relateds exist and are selective in respect to the. nature. and violence of attack

ifferent varieties the uncertainties have been multiplied. That more strains"-develop or will become known is a safe prediction. It must be borne in':<1 also that resistance is the ideal solution for disease problems other thande caused by, viruses and to develop varieties resistant to .virus diseases,:which are easy targets for bacterial or fungus pathogenes, will not answer,requirement. The responsibility of the plant breeder is seen to be one.: cannot be taken lightly, but it is also evident-that nature has provided

. ts of departure in the building of disease resistant varieties and theibility of improvement iby breeding has been amply demonstrated.

, The points of departure are not numerous but for some disease or groupdiseases they may be found in every species of sugar cane,even in Saccharilm'inarum, if we accept the rather inclusive array of original varieties assignedih~t species. These varieties, referred to as the "noble" canes because ofi1' aristocratic .appearance, have thereputation of being specially susceptible~lmost every disease or unfavourable condition. However, Badila, which is

r to S. offietinarum than to any other species yet erected, is unusuallytant to many diseases, including several of the virus group, and theormance of Badila is reasonably. satisfactory' in Queensland where, disease

'blerns are numerous and varied. The several varieties .' of S. sinense, whilebJ.ect to streak (also smut and numerous other diseases caused by micro­

'ganisms) are outstandingly resistant to. mosaic.'. S. spontaneuni. in its:luerous varieties is. not known to be affected by any virus -disease but is,'4dily attacked by downy mildew. 'I'hisepeciea, together with varieties of'.barberi have been and still are used'iu breeding for resistance to sereh.

intriguingyseeming enigma is presented in .the unverified report thatunnee, a variety assigned to the species S~ borberi and susceptible to mosaic

,ssed with Black Cheribon, a noble variety also susceptible to mosaic, gave'e to an immune hybrid in the F3 .generation; 'I'his questionable case isntioned because it is entirely possible, that mating susceptible varieties that: in fact hybrids heterozygous for mosaic resistance may give rise to resistanteven immune plants in the progenies. S.robilsturn from ~ewGuinea has11 proved susceptible to mosaic but that is no r.easonfor discouraging theof this valuable plant inbreeding for resistance to Iilosaicifit is crossed

.h a hybrid having some S.spontaneum blood. Incidentally' cuttings from'eased stools of S. rO'bustum sent to Washington from F'lorida have come UI)

lthy ina fairly .large proportion, proving that recovery takes. place readilythis species. In the foregoing comments on variety groups in relation toeases the current classification 6£ forms in the genus Saccharurn has been

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usq~ !~"on~<\ni",~,";<f~i~";e. \4".pJ"'I1~"·X"'QU'1'~,i"'fll.· MA"pIi()~Ogistsjj""dg,ueiids" ,",eu~t ""ti,ely in a,p-,enwllt.Olltbe ,l."w,aliQll ari~ Inrll",Idivision of species into subgroups or species is likely. .

From the consideration of the general aspects of the virus diseases asa whole attempt has been made to "philosophize" in the hope of presentingsome. stimulating and. directive viewpoints for research on the virus problemsperse and on'control.We now' take stock of progress in research and present

a brief synoptic account of the sugar-cane virus diseases.

,..-........~IIIIIIIIIIII...........,....~""7T ____IIII

The identity of the mottling Ofisugar cane in Puerto Rico with thestrepenziekte of Java, andthe yellow-stripe disease of Hawaii and other regions;.was finally recognized and' brought to attention by· the' investigatorssubject in 'Puerto Rico, and the infectious nature of the disease was .generallyacceptcd by them.. Adequate evidellce of its being infectious was still lacking;.however. The experiment aa eviden/3e was meagre and not free. froIll .-possibility of error. Theperpetuationo£ the disease through infected "seed·"I·cuttings was evident but nothing waslmownregardingsecondary dissemination;

to healthy plants in the field.

The disease now known.a~suga:r:cane mosaic has been the subject of:,inyestigations and reports bY various .workers, first in Java, later in Hawaii,and more recently in the West Indies,theUnited.8tates of America, Argentina,Natal, and India. In 1892, Van Musschenbroek [15] published adescriptionof 'the disease under the symptomatic name "gelestrepenziekte," orstripe disease, and in 1893 there appeared a multicolour reproduction ~hn",;-n~a portion of a sugar-cane leaf affected with the disease,. together withon its occurrence, by ArendsenHein [1]. Since 1919, the disea~e has peen-recorded as affecting not only sugar cane and other species ofbut also maize (Zeamays L.); sorghum (Sorghumvulga,re Pers.) and owec.species of sorghum millet (Penni~s(jtum glaucibm (L.) R. Hr.) ; and thegrasses DigitMia' s<Jm'guina,lis (L.). Scop., Paspalum bos'cialinumFlugge, Setarialutescens (Weigel) Hubb., S. Magna Griseb., PaniGum dicho,to'l'YlJijlor'umMichx..•Eleusine indJica{L.). Gaertn.,EchinobhlOaCru~galli(L.) Beauv., E.(L.) Link, and Brachiaria exterisa ·Ohase. The disease of maize reportedGuam, Hawaii, and Ouba, known as corn stripe, is distinctly different .j'""",-

mosaic in maize.

M. W.Beijerinck [2] in 1898, distinguished the virus as a contagious

fluid, and not a bacterium.

Summary of Results of Research.

MOSAIC.. History.-AdolfMayer [12] in 1886, gave the descriptive name,'

"mosaic" to the tobacco disease.