Vol. IV. No. 83. 



THE AGEICULTUEAL NEWS. 



189 



FUNGOID DISEASES. 



Ripe-rot or Anthracnose of Banana. 



This disease is widely spread ; it was first recorded 

 from Australia and has since been noted in the United 

 States. A very similar, if not the same, disease has 

 recently been noted on bananas in the West Indies. 

 The disease is caused by a fungus, Gloeospovium 

 musarum. 



The following description of the disease, by 

 Dr. N. A. Cobb, is taken from the Agricultural 

 Gazette of New South ^Vales (Vol. XIV, p. G38):— 



As soon as the fruits reached a length of about 3 inches, 

 and sometimes earlier, they began to change colour and to 

 shrivel, passing through greenisli-yellow, yellow, brown, or 

 French grey, to almost black. At the brown stage the 

 colour became pruinose, and the final blackening was 

 accompanied by a pink eruption of Gloeosporium spores. 



The spores occurred on all parts of the fruit, but in 

 some specimens they were most abundant on the basal half, 

 being particularly abundant at the very base of the stem. 



The disease extended to the entire bunch, which in 

 consequence was rendered worthless. 



No other disease-producing organism was to he seen on 

 the specimens sent, A^'hich included most of the middle part 

 of a bunch. 



The sender wrote that he felt certain that cold weather 

 had nothing to do with the matter. It was apparent that 

 the disease had attacked the fruit at an early stage of its 

 existence. 



Later, the fungus fruited freely on the main stem of the 

 Ijuncli of bananas. The facts observed seemed to establish 

 the ability of the fungus to prevent completely the fructifica- 

 tion of the banana. 



A considerable number of fruits suffer from ripe- 

 rots, caused by different species of Gloeosporlum. 

 Among the fruits are apple, pear, quince, guava, 

 tomato, egg-plant, etc. Dr. Cobb made .'i special study 

 of these rots, and came to the conclusion that the 

 fungus causing thenj was really one and the same in 

 each case. He conducted a number of cross-infection 

 experiments with successful results. For instance, he 

 inoculated bananas, tomatos, mangos, etc., with spores 

 of the ii[ie-rot fungus of the apple, with the result that 

 these fruits were infected and became diseased. 



Diseased fruits should be removed and destroyed 

 as soon as the rot is noticed, as otherwiise the whole 

 bunch will soon be infected and destroyed. 



Pod Diseases of Cacao. 



Three cacao pod diseases are known in the West Indies, 

 but only two of them are of great practical importance. 

 These are the 'Trinidad pod disease' caused by the fungus 

 riiytophthora, omnivom, and the 'brown-rot' caused by 

 Diplodia cacaoicola. This latter is the same fungus that 

 causes the 'die-back' disease of the stem. 



The PJiytopihthova, as its specific name implies, attacks 

 a large number of plants, mostly seedlings ; it is a marked 

 parasite. The Diplodia, on the other hand, is distinctly 

 a facultative saprophyte, and is cajtable of growing on 

 a large variety of dead substance?, including dead cacao 

 twigs, the dead husks of the pods, etc. 



Pods attacked Ijy Pliytophthora turn dark in colour. The 



darkening generally starts at one end, and in a few days, 

 under favourable conditions, spreads over the whole pod. 

 A white mould makes its appearance, after a time, on the 

 surface of the pod. It generally appears first in the furrows. 

 This white mould represents the reproductive organs of the 

 fungus. Numerous spores (conidia) are produced on this 

 mould, and these are carried by wind, etc., to other pods, 

 which in turn become infected. The conidia are large, 

 egg-shaped, colourless, and one-celled. 



The fungus mycelium spreads through the whole of the 

 inner tissues of the pod, oven attacking the seeds. Resting 

 spores, capable of retaining their vitality for a considerable 

 time, arc produced in the diseased tissues. The conidia 

 produced externally are delicate and soon die unless they are 

 carried to a spot suited for their germination. 



The brown-rot also starts as a small brown patch on the 

 pod, generally either at the insertion of the stalk or at the 

 free end. In from six or ten days later the pod is destroj'ed. 

 The mycelium of Diplodia also spreads to the interior of 

 the pods. It destro}'s the tissues both of the pod itself and 

 of the seeds. 



So far the two diseases are very similar; the two fungi 

 difier, however, markedly in their methods of reproduction. 

 The spores of Diplodia are formed in small chambers under 

 the skin of the ijod. Large numbers of them are produced 

 in each chamber, and finally the pressure on the skin becomes 

 so great that it is ruptured. The spores are expelled as 

 small heaps of black [lowder. On microscoDic examination 

 they are .seen to be elliptical in shape, dark-brown in colour, 

 and two-celled. The two fungi also difl!"er in their vegetative 

 hyphae, those of Diplodia being septate, while those of 

 Pht/tophthora are without septa. 



In dealing with both diseases, the most important 

 remedial mea.sure is the burying of all dead husks or shells 

 instead of leaving them on the surface of the soil to decay. 

 In the case of Pliytophthora, this measure destroj'S the 

 resting spores by which the fungus passes over from one season 

 to another. In the case of Diplodia, it destroys a convenient 

 breeding ground for the fungus. At the recent Agricultural 

 Conference, Mr. .1. H. Hart, F.L.S., stated that on one 

 estate in Trinidad, this treatment, systematically carried out, 

 had resulted in an increased yield of 2.5 per cent. 



Diseased pods, also, should be removed and buried or 

 burnt as soon as noticed. They will give no yield, and only 

 serve as a source of infection for other pods. 



Severe local outbreaks of Phytopjhlhora could be checked 

 by spraying the young pods in the aflFected locality with 

 Bordeaux mixture at intervals of, say, ten days. 



In all probability, both diseases occur in all caoao- 

 producing colonies in the West Indies. The relative 

 abundance of the two apjiears to depend on local conditions. 

 In Trinidad and British Guiana, for instance, Phytophthora, 

 is the more abundant and destructive. A very humid 

 atmosphere probably would favour Pliijtoj^hthora more than 

 Diplodia. It would be interesting to have accurate 

 observations on the relative aliundance of the two diseases in 

 Grenada, where cacao is grown without shade, and where, 

 consecpicntly, the atmosphere, round the pods, is less humid 

 than in Trinidad. 



In Surinam, there is another serious pod disease, caused 

 by the same fungus as that causing the witch broom disease. 

 The disease is known to the Dutch planters as ' versteening ' 

 (petrifaction). The fruits show first a discoloured patch, 

 which later becomes black. They are distinguished from 

 those attacked by other diseases by their hardness, which is 

 seen at once if they are cut. 



