Studies on the mechanical transmission of cocoa swollen shoot virus: some factors affecting virus multiplication and symptom development
1974
Adomako, D., Cocoa Research Institute, P.O. Box 8, Tafo,Ghana | Owusu, G.K., Cocoa Research Institute, P.O. Box 8, Tafo,Ghana
The presence in cocoa (Theobroma cacao L.) of cocoa swollen shoot virus inhibitors, the effect of pre-germination of cocoa beans on infection with the virulent strain A of this virus, and the kinetics of symptom development in cocoa seedlings were studied by manual inoculation of germinated and ungerminated cocoa beans with partially purified virus preparations and by inoculation with viruliferous mealybugs (Planococcoides 1'!ialensisLaing). Although germinated beans are practically resistant to infection with cocoa swollen shoot virus by mechanical inoculation, germination of beans did not affect their infection with the virus by mealybugs when the latter was investigated using 10 insects per bean. The presence of small molecular weight (dialysable) virus inhibitors was demonstrated in cocoa beans and leaves but there was a negative correlation between their concentration and the resistance of germinated beans to virus infection by mechanical inoculation. This phenomenon and the fact that other tissues of the cocoa plant can be infected with the virus by mealybugs but not by mechanical inoculation were attributed to the tissue specificity of the virus and the ability of mealybugs to introduce it into the tissues favouring multiplication and development. Percentage infection and the rate of symptom development in seedlings raised from manually inoculated beans were found to be related to in oculum concentration and the total surface area inoculated, which also determine the number of infective centers established and the optimal virus concentration in affected plants.
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