216 DISEASES OF TROPICAL PLANTS CH . 



widely distributed disease is caused by Fusarium 

 ly coper sici, Sacc., an organism which is very closely 

 related to the species which cause similar diseases on the 

 cotton, melon, and cow-pea. It is especially character- 

 istic of warm climates, lives in the soil, and probably 

 gains entrance to its host through wounds on the roots. 

 The diseased plants undergo a gradual wilting and 

 dying. The fibre-vascular bundles are discoloured and 

 filled with the white mycelium of the fungus. As the 

 disease progresses the part of the stem just above the 

 ground becomes covered with the mycelium and the 

 conidia. 



Fortunately this fungus does not maintain itself in 

 a soil which is free from the host plants as long as some 

 related species of this genus. Therefore, it is possible 

 to combat it advantageously by short rotation of crops. 

 Care should be taken to use seed from healthy plants. 

 Spraying is of little or no value. This disease is also 

 said to attack potatoes, egg-plants, etc. 



Bacterial Wilt, This is another wilt disease, but is 

 due to an entirely different organism. It is caused 

 by Bacillus solanacearum, Erwin F. Smith. It has 

 been reported from Western Australia and Straits and 

 Federated Malay States, and is quite common in the 

 Southern United States and in the West Indies. The 

 general appearance of the diseased plants is very similar 

 to the plants which are suffering from Fusarium lyco- 

 persici. The leaves wilt and the stem shrivels, chang- 

 ing to yellowish green, brown, and black, and sometimes 

 there is a gummy deposit on the surface of the stems. 

 A cross-section of the stem shows a discoloration of the 

 fibro- vascular bundles, and a microscopic examination 

 reveals the organisms which cause the disease. These 

 organisms also live in the parenchyma and in the bark, and 

 are transmitted from plant to plant by means of insects. 



The diseased plants should be pulled out and 

 destroyed. Spraying with Bordeaux mixture or other 

 fungicides is of no value ; but if a treatment to destroy 

 the insects can be given, it will be advantageous. 



