31S 



THE AGKICULTUi^AL NEWS. 



October 6, 1917. 



PLANT DISEASES. 



INTERNAL DISEASE OF COTTON 

 BOLLS IN THE WEST 



INDIES. 



The current number of the West Indian Bulletin (Vol. 

 XVI, No. 3, issued September 10, 1917) contains a paper by 

 \y. Nowell, D.I.C., Mycologist on the staff of the Imperial 

 Department of Agriculture, which deals with the facts 

 ascertained and the conclusions reached in the study, as yet 

 incompiete, of an affection of cotton bolLs in the West Indies, 

 characterized by the progressive staining and rotting of the 

 lint in green unopened bolls of healthy external appearance. 



Such staining is shown to be due to the infection of the 

 contents of the Isoll with certidn specific fun^ii, previously 

 de.soribed by the author, or with bacteria aa yet undefined; 

 which organisms gain access to the interior of the boll by 

 means of the punctures made by bug?, mainly Dysdercus 

 spp. (cotton stainers) and Nezara viridula (green bug). 



Four .species have been found, referred to for the present 

 by the letters AD. All bear elongated spores in sporangia 

 which originate as expansions of simple hypbae. In species 

 A the spores show no orderly arrangement. In .species B 

 they occur in two conical bundles interlocking at the base; this 

 form ai>pears to correspond with Ereiuotheciwa cyvibalariae, 

 Borzi. In species C and IJ the spores typically lie in two 

 equal groups end to end, some distance apart but connected 

 by the whip-like appendages of the .«pores. The thallus of 

 species A-C is typically hyphal; that of D is typically yeast- 

 like, but assumes the hyphal form under some circumstances. 

 Species closely resembling 1 ) have been described as forming 

 the genus Nematospora. P.oth the genera named occur so far 

 as is known only in fruits. 



In bolls which are approaching to full size and in which 

 the lint is well developed, the result of an infection is the 

 production of a stained patch due to the growth of the 

 invading fungus or bacterium on the lint. According to 

 circumstances this may be small, or may, alone or with other 

 infections, spoil the contents of the whole lock. The effect 

 on younger bolls is more uniformly sevtre, owing to the more 

 susceptible condition of the boll contents, and the longer time 

 afforded for the growth of the invading organism. Many- 

 such bolls are shed before nialurity, and in the remainder the 

 contents of the infested locks are more or less coriipletely 

 rotted. 



The prevalence of the affection is much greater in some 

 islands than in others, and in some seasons than in others. 

 Heavy losses from the disease are experienced only in the 

 second half af the picking season. In the years and situa- 

 tions most marked by its prevalence the losses in the first 

 picking of May-planted cotton (September-October-November) 

 are commonly negligible, and have not been found to exceed 

 20 per cent, in the local outbreaks which have occurred, but 

 during the second picking (November December . I n.nuary) 

 they rise very rapidly and in the last-mentioned month may 

 be close upon 100 per cent. The yield of early planted 

 cotton is thus not seriously affected but that of late cotton is, 

 on occasion, almost totally destroyed. 



A review of the entomological literature of the subject 

 show.-, that the idea once gecerally held that plant bugs give 

 rise to staining of cotton by means of their excrement and 



through being crushed in the gins has been widely ques- 

 tioned, but that no convincing explanation has-been offered 

 of the extensive staining often experienced in connexion with 

 bug attacks. 



Certain pathologists have suggested that in.sect punctures- 

 afford means of entrance for boll- rotting bacteria. 



The occurrence in the West Indies of internal boll 

 disease as defined m this paper was noted in the year following 

 the resumption of cotton growing in 1902. The affection 

 has since been found to be generally distributed in the 

 British islands where cotton is grown, from .Jamaica through 

 the Lesser Antilles to British Guiana. 



Experiments have demonstrated without exception the 

 dependence of the disease on the infection of bug punctures. 

 It seems most probable that, at least in the case of the fungi 

 concerned, the infecting organisms are carried by the bugs 

 themselves. 



Under ordinatj' conditions fungoid infections greatly 

 predominate over those due to bacteria, but under circum- 

 stances which appear to be connected with wet weather, the 

 proportion of the latter miy be largely increased. Weather 

 conditions have not been found to affect the occurrence of 

 fungoid infections. 



The results of plant bug attacks on the boll, as seen when 

 the punctures have remained uninfected, are (1) the production,, 

 observed in young bolls only, of dead brown patches of lint, 

 which are small and localized ; (2) the occurrence of, 

 proliferated tissue on the inner surface of the carpels and, 

 on punctured seeds ; (3) the death of a certain number of 

 feeds in bolls severely attacked. The amount of stained 

 lint produced in this way is negligible. The returns of 

 stained liot obtained in these islands are mainlj- due, 

 in varying proportions, to (a) internal boll disease, and 

 (b) ordinary bacterial disease. The latter only becomes, 

 serious in wet weather. 



The varying incidence of the disease is shown to depend 

 in general on the relation between the time of planting, the, 

 length of the crop period, and the time when infestation 

 with stainers occurs. 



The infestation of the cotton fields with stainers origin- 

 ates from waste land on which their wild food-plants exist,, 

 and proximity to such a source leads to earlier and more 

 severe invasion. Migratory flights of stainers, with an, 

 unknown range, have however been ob.served. 



The principal food-plants on which the stainers breed 

 freely out of the cotton season are the silk-cotton tree 

 (Eriodendron) ami the mahoe (Thespesia) ; they also breed 

 to some extent on various Malvaceons herbs or shrubs. 

 They feed, without breeding, on a large variety , of other 

 plants. 



An addendum to the paper states that when this was 

 already in print specimens of diseased tomatoes and cow- 

 peas, received from the Sr. Vincent Experiment Station, were 

 found to be heavily infested, the tomatoes with species A 

 and the cowpeas with species D. In both cases the fruits 

 were externally sound, but bore small scars such as would 

 be produced by bug punctures, and had internal proliferations. 

 On cutting open an affected tomato one or more sectors 

 were found blackened, the placental tissue and the seeds 

 infested with the fungus, and the Juice charged with very 

 numerous spores. In the case of the cowpea,?, minv seeds 

 still succulent showed a brown dot on the testa with a cir- 

 cular fungus infestation on the cotyledon beneath. The 

 subsequent growth of the fungus .shrivels the cotyledons 

 very severely by the time the seed should be ripe. 

 A total loss of crop on one plot of cowpeas is reported 

 which, according to the s|)ecimens sent as representative, was 

 due almost entinly to this affection. 



