THE AGRICULTURAL NEWS. 



Septemisei: 13, 1913. 



FUNGUS NOTES. 



WITOH BROOM DISEASE OF CACAO. 



A [laper by J. B. liorer has just been issued b)- the 

 Board of Agriculture of Trinidad and Tobago, which shows 

 that in all probability the witch broom disease of cacao is 

 caused by a Basidiomycetous fungus and not by Colleto- 

 Iricliuii: In fiUcum, as was formerly supposed but never 

 definitely proved to be the case. 



As is well known, the above disease has occasioned 

 severe loss to the cacao industry of I»utch Ouiana, and has 

 occurred in British Guiana and the fact that up to the time 

 of the present investigation the parasitic origin of the 

 malady was a matter of some uncertainty, its study constituted 

 one of the most interesting of tropical pathological problems, 

 ilorer made two visits to Suriname in connexion with the 

 disease; the first visit was for the purpose of deciding 

 whether or not the disease existed in Trinidad; the second 

 visit was taken to carry out a more detailed mycological study 

 of the disease and to make observations on methods of 

 control. The first visit led to the formation of the conclusion 

 that witch broom disease is not present in Trinidad. The 

 second visit has materialized in the form of the present piper. 



E.\RLV INVESTIGATIONS UXSUCCE.?>FrL. 



Kitzema Bos in 1900 was the first to make a microscopic 

 study of witch broom disease known to the Dutch under 

 the name Kndlnten. This investigator considered the trouble 

 to be due to Exoascus t/ieohromae although no figures or 

 description of the fungus were given. In 1901, specimens of 

 the disea.sed tissue were sent to Kew, and to the Imperial 

 Department of Agriculture at Barbados, The material sent 

 to Kew was examined by Massee who found neither asci nor 

 spores of an Exoascus. In Barbados, Howard, too, was 

 unable to find any evidence of an Exoascus but noticed 

 a species of Fusarium fruiting on the bark which he stated 

 might have been connected with the disease. The malady 

 was first studied in detail by Went. This worker found an 

 intercellular mycelium in the tissues of all parts of the 

 witch broom including stems, petiole, leaf blade, calyx, 

 stamens and pistil. It was lacking only in the im- 

 mediate growing point. No fructifications were found, 

 and Went concluded that E.vo'ncus tlieobromat- was not 

 likely to be connected with the disease. He obtiined 

 a pure growth of the mycelium which he noticed 

 in the tissues but was not able to produce fructi- 

 fication nor were the infection experiments successful. 

 He came to the conclusion that infection very probably took 

 place in the bud or in the shoot just beneath the bud as he 

 never found the fungus growing through sound tissue from 

 one to another. 



From a study of dried witch brooms sent to the United 

 States Department of Agriculture, Charles has suggested 

 a possibility cf a species of Lasiodiplodia being the cause of 

 the trouble. 



THE COLLETUTUlc IH M OF VAN II.\LL AND DllOST. 



In 1905, van Hall and Drost began an extended study 

 of the malady. They i.solated a Colletotrichum from the 

 diseased tissue and it aiii>eared to be a new si^ecies to which 

 the authors gave the name C. lu.iitinnn. This fungus has 

 hitherto been regarded as the cause of the malady. 



Although Kredholme in his English translation of 

 a paper by these investigators stati-s that inoculations 

 had demonstrated the particular fungus origin of the 

 disease, this rendition is demonstrated by Rorer to be 

 inaccurate. A'an Hall and Drost reported no inocula- 



tion experiments of their own, and in the paper referr- 

 ed to, reference is evidently made to Went's inoculations 

 which were not successful as has already been mentioned. 

 Van Hall and Drost agreed with Went that the pathological 

 condition known as 'indurated' pods is caused by the same 

 fungus as witch liroom disease, and in addition called attention 

 to 'star blooms' — the production of great numbers of crowded 

 blossoms on the cushions — as another symptom of the disease. 

 (See Aijrkulliiral A'ews, Vol. IX, p. 57.) Among these 'star 

 blooms' vegetative shoots often develop into small witch 

 brooms. 



INKAPPINC. METHOll OF rOXTKOL. 



In the treatment of the disease the authors gave 

 up spraying with Bordeaux mixture on the score of 

 inefficiency and expense and advocated the cutting back or 

 inkapping method of control. Briefly stated, this method 

 consists in removing the whole crown of the tree by cutting 

 off the main branches 2 or 3 feet above the point of forking. 

 As soon as the trees begin to put out new shoots they must 

 be carefully watched, and all witch broom must be cut off and 

 burned. 



In connexion with C. litririciun as a possible 

 cause of the disease, mention may be made of the 

 fact that although witch broom such as described from 

 Suriname has never been seen in Trinidad, a fungus 

 identical in microscopic api)earance to C. hiiiticnm is 

 commonly found there, but inoculation experiments have 

 shown it to be merely a saprophyte or possibly a weak 

 parasite. 



Both Went and van Hall have already pointed out 

 that mycelium is always present in the diseased tissues of 

 stems, leaf, flowers and pod. As soon as the branch begins 

 to die .several species of fungi are found fruiting on the sur- 

 face. Rorer fniind no evidence however of an l]xoa.scus. 



A FUNGUS WITH I LAMP-CONNEXIONS. 



During the last visit to Suriname, Rorer made sixty-one 

 cultures from the inner tissues of diseased material. Every 

 one of these cultures was apparently pure, and of the same 

 fungus. After about two weeks, the white surface of the 

 agar slant was covered with a matted surface of mycelium 

 which had a liglit yellow colour and showed slightly accen- 

 tuated concentric rings of growth There wa.s no marked 

 aerial development of hyphae. In older cultures, the mycelium 

 became felt- like and slightly darker in colour. The fungus 

 from the diseased pods was identical wiih that obtained 

 from other tissues. No fructitications were produced on the 

 mycelium The only cltte to the identity of the fungus was 

 the fact that the mycelium possessed clamp connexions (which 

 Went evidently missed) and this naturally places it with the 

 Basidiomycetes. Clamp connexions were observed in all 

 sixty-one cultures. Fresh material sent to Hedges at Wa,sh- 

 ington were found independently by this investigator to 

 contain mycelium possessing clamp connexions both in the 

 tissues and in culture. 



It may be mentioned here that owing to the fact that 

 witch broom disease docs not occur in Trinidad, inoculation 

 experiments there are out of the question, but these are 

 being conducted bj' Hedges at Washington on cacao plants 

 under glass, and in due course a paper will be published by 

 Rorer and Hedges following on this the preliminary report 

 on the disease. 



To continue I lorerV observations in Suriname, it .should 

 be stated that this investigator endeavoured to find out 

 whether there was .any likelihood of ants conveying the 

 disease in the form of the mycelium which freiiuently occurs 

 in small masses on the surface of the bark. No evidence 



