254 



THE AGRICULTURAL NEWS 



AtrcJU.sT 5, 1911. 



FUNGUS NOTES. 



TWO BANANA DISEASES OF THE 

 WEST INDIES. 



In the Aijyifultuial News, Vol. X, p. 110, appeared an 

 article dealing with some diseases of the banana which occur 

 in certain parts of the West Indies and of Central America. 

 Since its issue, two valuable papers have appeared treating 

 of two of the most important diseases at greater 

 length than has been the case in previous publications. 

 These two diseases are somewhat similar in outward appear- 

 ance, though dirterent in origin. There is a considerable 

 possibility that one or both may occur in some of the islands 

 of the Lesser Antilles and, in consequence, it is thought that 

 a further account of the two diseases may be of interest. 

 The original papers from which the information given below 

 is taken are: A Bacterial Disease of Bananas and Plantains, 

 by liorer, issued as a publication of the Board of Agricul- 

 ture, Trinidad, and The Panama Disease, Parts I and II, by 

 E. Essed, B.Sc, published in the Annals of Botany, 

 Vol. XXV, p. 343. 



THK PANAM.v DisKAsi'; TMs occurs in Costa Hica, 

 Panama, Surinam, Trinidad and probably in Cuba, while 

 according to report it is also to lie found on the Atlantic side 

 of Nicaragua, Honduras and Guatemala. It is of consider- 

 able importance in the first two countries, though the damage 

 done there would not appear to be as great as that inflicted 

 on the banana plaiitations in Surinam. The most susceptible 

 variety of banana is the Gros Michel, though various others, 

 both of bananas and plantains, are also said to be more or less 

 liable to be attacked by the disease. It was thought for some 

 time that the Congo variety was more or less immune, though 

 recently it has been found to be attacked quite frequently, in 

 Surinam. 



In the first stage of the disease, according to Essed, the 

 symptoms consist of a peculiar withering of the leaves along 

 the margin, while discoloration may be observed along 

 a mid-dorsal line on the midrib. Sometimes the youngest leaf 

 withers first, and is unable to unfold, while the older leaves 

 are healthy; at other times, the first symptoms appear on the 

 older leaves. In the next stage of the disease development 

 ceases, the leaves droop and the plant looks as though it were 

 suffering from drought Wrinkles tlien appear on the sheath 

 and midrib of the leaves; and finally the latter dry uji, and the 

 pseudo stem falls over. ^ 



On examining the rhizome of an infected plant, it is 

 seen that this is the part principally affected. The healthy 

 whitish colour is replaced by a yellowish hue; while reddish- 

 brown spots and streaks are scattered through the infected 

 parts, and a yellowish or brownish mucilage exudes from the 

 cut ends of the slime canals. The roots are usually free from 

 disease until the tissues at their base become affected, so that 

 it is evident that the fungus does not enter through them. 

 The water-starved appearance of diseased plants is due to 

 the occurrence of masses of mycelium and spores of the 

 causative fungus within the vessels of the vascular bun- 

 dles, which constitute the water-carrying region. From 

 these the fungus can spread into the cells of the ground 

 tissue, where it causes an almost complete rot. 



Essed has given the name Uslllafjinoidi'lla musaeperda 

 to the causative urganism, and has siiown, by means of infec- 

 tion experiments, that this fungus, and not any of the bacteria 

 associated with it, is actually responsible for the disease. The 

 fungus itself has many curious reproductive arrangements, 



but includes among them a simple Fusarium stage (see Agri- 

 cultural iVifi'v Vol. IX, p. 175). Such a reproductive form 

 has been found on tlie fungus as.sociated with a similar disease 

 of bananas in Cuba by Dr. Erwin Smith, and with the 

 Panama disease, as known in Trinidad, by Rorer. The 

 Surinam fungus belongs to the group Hypocreales (see Agri- 

 cultural News, Vol. IX, p. 127), and is distantly related to 

 the genus Nectria. Another closely related species, Ustila- 

 ffinoidella oedipigera, was found by Essed to be responsible 

 for elephantiasis of the banana in Surinam — a disease men- 

 tioned in the article in the Agricultural Neivs first referred 

 to above Another closely related species is responsible for 

 a disease of rice, in the same country. 



There is nothing that can be done to save plants that 

 have once become affected with the Panama disease, and at 

 present no reall}' successful measures have been discovered 

 for preventing its spread. All that can be undertaken, is to 

 make every attempt to discover a really immune variety, and 

 then to propagate this. 



MOKO DISEASE. Under this name, Rorer has described 

 a bacterial disease which attacks particularly the ' moko' fig 

 variety of plantain, much employed in Trinidad as a shade 

 plant for young cacao. It also occurs on the Creole and French 

 varieties of plantain {Musa paradisiaca), and on the dwarf 

 or Cavendish banana {Musa chihcnsis). It does not attack 

 the Gros Michel banana or the Manila hemp jilant {Musa 

 te.ciilis) to any considerable extent. 



The disease usually appears first in the lower leaves. 

 The leaf blades droop a little more than usual, and have 

 a slightly yellowish tinge. Then the petiole, or stalk, of one 

 of the leaves breaks just below the leaf blade, and those of 

 the other leaves soon follow. Eventually, the terminal leaf 

 also bends over, and the plant dies and rots down to the 

 ground. When the disease is not severe, or when the plant 

 does not become infected until after it has formed a bunch of 

 fruit, it may remain perfectly healthy in appearance; many 

 of the young fruits, however, do not mature, but eventually 

 become black and rotten. When the pseudo-stem is cut 

 across, it is .seen that the vascular bundles are discoloured, 

 the colour varying from pale yellow to dark brown or bluish 

 black. These discoloured bundles run back into the true 

 stem, or rhizome, and thence into the young suckers and 

 buds. Sometimes, in badly disea.sed plants, the tissues of 

 the leaf stalks and stems are broken down completely, so 

 that fairly large cavities are formed, which like the vessels, 

 are filled with bacteria. When kept for a short lime, trans- 

 verse sections of the leaves or stem become covered on their 

 cut surface with bacterial drops, which exude from the 

 vascular bundles. 



The symptoms of this disease are very similar to those 

 of the Panama disease, but it may be distinguished as 

 follows: Although the vascular bundles of plants attacked 

 by the Panama disease are discoloured and often contain 

 bacteria, yet this bacterium is a gas former, and is not patho- 

 genic. .\gain, the longitudinal splitting of the leaf sheath, 

 which is a characteristic of the Panama disease, is not found 

 in plants attacked by the moko disease. The Panama disease 

 is due to a fungus which occurs plentifully in the infected 

 bundles. The Gros Michel variety is that principally affected 

 by the Panamft. disease, while it is practically inmiune to the 

 moko disease. 



The moko disease may be controlled, according to Rorer, 

 by the following sanitary measures; the destruction by 

 burning of all diseased plants when found; the sterilization, 

 by fire, of all tools and implements used in the work; and the 

 planting of healthy suckers. 



