S18 



THE AGRICULTURAL NEWS. 



October 24, 1914. 



FUNGUS NOTES. 



WILT DISEASE OP LEGUMINOUS 

 PLANTS. 



A recent (x-eurreuee in .Mdutsenat on Ttphrosia Candida 

 of wilt disease, of the kind which has had veiy serious etfects 

 on leguminous plants in many parts of the world, renders it 

 advisable, in view of the expected increase in the cultivation 

 of leguminous food crops, to summarize the available informa- 

 tion respecting the disease. 



The ilontserrat specimens e.xhiliit the usual signs of 

 attack by Fusarium wilt disease: the vessels are tilling up 

 with colourless hyphae, the wood is turning brown in places, 

 and .spores of Fusarium type are being produced. The 

 .specimens examined are not in an advanced stage so far as 

 their general appearance goes. The wood is mostly sound, 

 the ti.ssues external to the cambium are softened but not 

 disintegrated, yet the roots bear on the outside very numer- 

 ous almost mature perithecia of Neocosmospora msmfecta, 

 Erw. Sni. 



This is the fungus \\hich for many years has been 

 regarded as the perfect stage of the widely distributed 

 Fusarium wilts of cotton, okra, melon, and amongst others 

 a wide range of leguminous plants, including cowpea, 

 pigeon pea, chick pea, indigo and Crotalaria. It" has been 

 found in association with such diseases in North America, 

 Africa and Asia. So far as is known to the writer it has 

 not previously been identitied from the West Indies. 



The history of the investigation of the disease is some- 

 what complicated. E. F. Smith published in 1899 the 

 results of prolonged studies of wilt diseases of cotton, cowpea, 

 and melon. He found that all were due to closely similar 

 l)arasites, which gave rise to the same type of disease in 

 tteir respective hosts, and produced morphologically indis- 

 tinguishable Fu.sarium and Cephalosporiuni forms of conidial 

 fvuctitication. On each host were also found the perithecia 

 of an Ascomycete, whose spores gave rise in pure cultures to 

 conidial stages like tho.se found on the diseased plants. 

 Attempts to produce the disease on its various hosts by 

 inoculation from pure cultures derived from the ascospores 

 were unsuccessful, and though it could readily be produced 

 by inoculations from cultures derived from the conidia found 

 on the plants, such cultures could not be induced to form 

 perithecia. While it was admitted that the chain of evidence 

 was incomplete, the presumption of the continuity of the dis- 

 ease-producing fungi with the Ascomycete was so strong, that 

 tlwy were regarded as identical: and the name JVeocosmosj^ora 

 vasinfecta, based on the perithecial form, was given to the 

 whole assemblage; the forms on the cowpea and melon, 

 owing to the failure of cross inoculations, being distinguished 

 as varieties under the names tracheip?dla ami nivea. 



A. Zimmerman found the perithecia of Neocosnio.spora 

 in (ierman East Africa on cotton in 1904. E. F. Butler in 

 1910 published the results of his investigations of Fusarium 

 \vilt diseases on cotton, pigeon pea, gram (chick pea), and 

 indigo in India. He found the perithecia of Xeocosmospora 

 occurring on the diseased roots in the same way as Smith 

 had described, but in a long series of experiments he failed 

 to secure infection by inoculations with cultures derived 

 from the ascospores, or to obtain perithecia in cultures of 

 proved parasitic nature derived from the diseased tissues. 

 In the following year B. B. Higgins in North Carolina also 

 reached the conclusion that the parasite on cowpea was 

 distinct from the perithecia-forming fungus. H. W. 

 AVollenweber has confirmed these results, and has pointed 



out that in cultures, certain differences occur between the- 

 conidial stages of Neocosmospora and the jiarasitic forms. The- 

 opinion is now generally held by mycolr.gists that Neocosmos- 

 pora vasinfecta is a harmless saprophyte, whose conidial 

 stages, though closely resembling those of the fungi which 

 produce the wilt diseases in question, are in reality tjuitfr 

 distinct from them. At the same time the constancy of the 

 association is a curious feature, unless Neocosmospora exists 

 as a saprophyte much more commonly than it is at present 

 known to do. For the pre.sent the parasitic forms obtained 

 have been returned to their old position in the genus Fusa- 

 rium. Much work has fieen and is being done in the exact 

 comparison by means of cultures of the members of this large- 

 and perplexing as.semblage of forms: and considerable 

 progress has been made in this direction. The fact is emerg- 

 ing that the wilt disease parasites found on various hosts are 

 separate forms or species, and are not interchangeable. Such 

 knowledge is very important in its practical bearing on 

 rotation of crops, since it enables a choice to be made of 

 a crop not susceptible to the wilt disease of the one pre- 

 ceding it. 



The deep-seated nature of the disease obviously renderi*. 

 any external treatment of affected plants hopeless, and the 

 use of sprays for prevention is of no avail, since all experience 

 goes to show that infection takes place to a very large extent 

 through the soil, which retains infective material in some 

 form for a period which must be measured in years. In 

 view of the latter fact it is obviou.sly very important in the 

 case of small outlireaks or sporadic cases to dig up and burn 

 the affected plants, while manure which is open tf) the 

 suspicion of containing infected material should not be used 

 for crops of the same allied kinds. 



Since the classical example of a disease-resisting \ai'iety 

 occurred in connexion with wilt disease of cotton, this avenue 

 i>f escape is hopeful in the case of similar disea.se of other 

 plants, and it has in fact been followed with success. Tlui.<4 

 varieties of cowpea and melon have been developed which 

 will thrive under conditions of soil infection which absolutely 

 prohibit the growth of the ordinary sorts. 



So far as the West Indies are concerned, Fusarium wilts, 

 with the exception of the Panama disease of bananas, do not 

 appear to have attracted much attention, and may therefore 

 be presumed to be uncommon or absent from other crops of 

 any importance. It is an interesting fact that the Rivers' 

 strain of cotton, from which practically all the Sea Island 

 grown in the West Indies is descended, was selected as 

 resistant to wilt disea.se, and has either maintained its resis- 

 tance or has not been exposed to infection here, the latter 

 being an improbable alternative. A case of severe damage 

 to a crop of pigeon peas is recorded as occurring in Trinidad 

 about 1900. A fungus was found on that occasion which 

 was regarded as an immature Nectria. 



DOWN THE ISLANDS. 



ITEMS OF LOCAL INTEREST. 



ST. viNCE.NT. The Agricultural Superintendent 

 (.Mr. W. N. Sands) returned to the colony from six month.s' 

 leave of absence in England by the Royal Mail during- 

 October. In this island, cotton growers though viewing with 

 apprehen.sion the position as regards cotton are for the 

 present confining attention to the crop soon to be reaped. 

 During this time they will have an opportunity of con- 

 sidering to what extent, if any, reduction in area should l»e 



