248 DISEASES OF CROP-PLANTS 



Symptoms. 



The presence of the disease is first shown by a slight drooping 

 and yellowing of the lower leaves, similar to the effect of drought. 

 A little later the petiole of one of the leaves gives way just at 

 the base of the leaf-blade, and all the other leaves quickly fail 

 in the same way. Eventually the terminal leaf bends over and 

 the plant dies and rots to the ground. The longitudinal sphtting 

 of the leaf-sheaths characteristic of Panama disease is absent 

 from this affection. 



" Transverse sections of the pseudo-stem show that 

 practically all the vessels are discoloured, the colour ranging 

 from pale yellow to dark brown or bluish black, and filled 

 with bacteria. The discoloured bundles run back into the 

 true stem and thence into the young suckers and buds. Some- 

 times in badly diseased plants the tissues of the leaf-stalks 

 and stems are broken down completely so that fairly large 

 bacterial cavities are formed. 



" If transverse sections of leaf or stem are allowed to stand 

 for a short time the cut surfaces soon become covered with 

 bacterial drops which have been forced out from the ends of 

 the bundles. If the sections when freshly cut are put in large 

 covered dishes away from the air, pure cultures of the organism 

 may be obtained directly from these drops. If the disease 

 is not severe, or a plant does not become infected until it has 

 formed a bunch of fruit, it may remain perfectly healthy 

 looking, but many of the young fruits, or ' fingers ' do not 

 properly mature ; they remain small and eventually become 

 black and rotten. In such cases it is found that there are some 

 discoloured bundles filled with bacteria in the leaves, stem, 

 fruit-stalk, or fruits. When diseased suckers are planted the 

 terminal leaf frequently turns black and dries up, so that the 

 plant dies " (Rorer). 



Causation. 



The organism was isolated in pure culture and was found in a 

 series of experiments to reproduce the disease in typical form 

 from inoculations made on the petioles of young leaves. In 

 several cases the whole stool was infested and killed. 



The bacterium was distinguished in cultures by the blackening 

 produced on potato cylinders. It is short lived and loses its 

 pathogenic power quickly. Control has been effected by sanitary 

 measures : digging up and destroying diseased plants as soon as 

 they are found and sterilizing by fire the implements used. 



Eelworm Black-Rot, 

 In Grenada the banana known as the bluggoe, a cooking 

 variety extensively grown as temporary shade for cacao, is 



