206 



THE AGRICULTURAL NEWS. 



June 21, 1913. 



FUNGUS NOTES. 



THE PANAMA DISEASE OF BANANAS. 



Those who are interested in the cultivation of bananas 

 will be aware of the existence of the Panama disease, of its 

 infectious nature and devastating effect, and of the contro- 

 versy that has arisen as to the identity of the causative 

 organism in different parts of the Western Tropics. It may 

 be remembered that the subject was dealt with at consider- 

 able length in the Agricultural Neics, Vol. XI, pp. 126, 127, 

 142 and 143, where available literature on the disease was 

 summarized and discussed by the then Mycologist to this 

 Department. 



One of the latest additions to the literature on the subject 

 is a paper in the /liillftin oMhe Dej 'art merit of A'jriculturt , 

 Jamaica, for January 1913, which describes an investigation 

 of the disease in that Colony, by S. F. Ashby, B.oc, the 

 Government Microbiologist. 



It appears, from this paper, that the typical symptoms 

 of Panama disease were first observed in Jamaica early in 

 1912. The cases were of a sporadic nature. Referring to 

 the external signs observed, it is pointed out that the yellow- 

 ing of the leaves and their eventual breakage from the 

 main axis, cannot be relied upon in view of the fact that such 

 symptoms can often be attributed to drought. A great deal 

 of attention is given, therefnre, to the internal symptoms and 

 to the study of the characteristics of the organism which 

 was isolated. 



In regard to the former aspect, it is stated that a section 

 across the bull> or head of a diseased sucker will show 

 minute discoloured dots corresponding to the positions of the 

 vascular strands. The colouring may be yellow, orange, 

 claret-red, purplcred, and in advanced stages dark-brown. 

 The writer was able to trace in some cases the discoloured 

 bundles from the bulbs of the affected suckers through the 

 connecting necks into the parent root-stocks. 



The examination of diseased tissue microscopically 

 revealed colourless septate hyphae closely adpressed to the 

 inner walls of the vessels. Hyphae could not be seen outside 

 the vessels. ^licroconidia were also present in the vessels, 

 but were never olistrved in quantity sutticient to lead to 

 the view that they caused serious obstruction. 



Cultures were made from different parts of diseased 

 tissue — from bulbs, roots, leaf-sheaths and stalks, with 

 strands in all stages of discoloration; and they always 

 yielded the same fungus. This organism was seen to have 

 a typical star-like appearance when grown artificially on 

 media. It produced three forms of spore-bodies: (a) micro- 

 conidia (similar to those observed in tlie vessels) formed 

 near the surface or under the surface of the medium, (b) 

 macroconidia, being, when mature, four-celled, sickle-shaped 

 and much larger than the microeonidia, (c) chlamydospores 

 or gemmae (resting spores). 



The author therefore describes the fungus as a Fusarium, 

 the microeonidia being the Cephalosporium stage. That no 

 perithecial stage was "btained will be carefully noted, since 

 this circumstance provides the chief point in which Ashby's 

 results disagree with those of Drost in Surinam. 



As well as isolating the parasite just referred to, Ashby 

 found another Fusarium on decayed banana plants free from 

 symptoms of Panama disease. This organism was grown in cul- 

 ture and its characteristics detei^mined with sullicient accuracy 

 to render the two fungi distinguishable. They are apparently 

 different species. The Panama disease Fusarium (Fusarium A) 



differed markedly from the saprophyte (Fusarium P.) by not 

 developing a typical Cephalosporium stage, nor sclerotia. An 

 important diagnostic feature is the fact that the waxy 

 masses of conidia of species B become dark-blue, especially 

 on bananas, and look very like the similarly coloured 

 sclerotia of species A. 



No inoculation experiments have yet been performed 

 with either fungus. 



Leaving the purely botanical observations, and passing 

 over the author's discussion of the literature on Panama 

 disease*, attention may be given next to the treatment and 

 prevention of the disease. 



As in most other diseases, once the fungus has gained 

 entrance little can be done to save the plant. The effect of 

 the fungus is to choke the vessels thereby curtailing the 

 plant's water supply. It is also believed that a toxin or poison 

 is secreted by the organism. The fact remains that preventive 

 measures only are of use Of these, the cultivation of 

 resistant varieties may be considered first. In this connexion, 

 the author advocates the planting, in infected areas, of the 

 Silverskin and Apple bananas, which are edible varieties, and 

 although susceptible, are much less so to the disease than 

 Gros Michel. Reference is next made by the author to 

 the proclamation issued in June 1910 forbidding the impor- 

 tation of banana plants or labourers' implements from 

 Trinidad and Central and South America. 



As regards the destruction in Jamaica of diseased 

 plants, it is stated that the boundaries of the affected areas 

 are fixed at a distance of one chain from the nearest 

 diseased stool: each tree is cut down and repeatedly charred 

 and then buried in freshly slaked lime. Although the des- 

 truction of the plants in this way was as thorough as could be 

 reasonably expected, enough infected material remained to 

 make replanting undesirable for a time A small plot on 

 one area was railed oft" and replanted six months ago; 

 a number of the young suckers have already shown signs of 

 the disease. The question is raised as to whether the 

 Fusarium can live in the soil as a saprophyte. The presence 

 of sclerotia would lend to support this speculation. 



In conclusion, the writer api)ears to attach sufficient 

 importance to such outbreaks as have alreadj- occurred in 

 Jamaica as to advocate the introduction of the I'ongo 

 banana, and the hardy, but much maligned dwjrf banana, 

 called 'Governor' in Trinidad, which, though somewhat 

 coarse, is a heavy yielder, and can be carried successfully 

 tincrated from the West Indies to England, and be readily 

 accepted by importers. 



Ne'W Exotic FutJgi. — It is stated in the Kew Bulletin, 

 No. 3, 1913, that six new fungi from various parts of the 

 Tropics have recently been identified at Kew Of those 

 which are likely to be of the greatest interest in the West 

 Indies :uay be mentioned (Hi^osporiuia tovo/'hiltan, Wakefield, 

 which was collected by Mr. F. W. South, H.A., late Mycolo- 

 gist of this 1 )epartment, in St. Vincent, on the petiole of 

 the coco-nut palm (Cocas nucifera). The second one of 

 interest is an Aseomycete, identified as Apion/iorium atrutn, 

 Massee. This organism was sent from Kuala Lampur 

 F.M.S., by Mr. C. K. Bancroft. It was found on the dead 

 branches of Para rubber trees but is not considered as a para- 

 site. Three of the new fungi described, developed on a small 

 piece of cattle dung forwarded from Singapore, Straits 

 Settlements, by Mr. I. 11. Burkill. 



* It may, however, be noted in this connexion, that Ashby 

 regards the disease in Surinam a.s identical with that in Panama, 

 Costa Ricn. Jamaica and Trinidad, ai\d probably witlitliit in 

 Cuba. 



