GENETIC-STUDY OF COCOA (THEOBROMA-CACAO L) BEHAVIOR TOWARDS BLACK POD DISEASE CAUSED BY PHYTOPHTHORA MEGAKARYA

Genetic study of cocoa (Theobroma cacao L) behaviour towards black pod disease caused by Phytophthora megakarya. The relationship between yield and black pod disease of cocoa caused by Phytophthora megakarya has been studied over 3 years in a diallel 6 x 6 trial set in Barombi-Kang experimental station (Cameroon) in 1974. The general combining abilities were the only significant factors on effective yield and black pod losses. The superiority of the parent UPA 134 was confirmed. Logistic models were used to define the parameters of the epidemic dynamics. A diallel analysis of these parameters was suggested. The maximum speed of disease propagation was heritable and the black pod losses were dependent on this parameter. The classification of the clones was different from that obtained with pod artificial inoculation tests. The vertical pod distribution in the trees and pod load of the different crosses could not explain this divergence. A hypothesis was proposed to :explain the clone classification differences between these 2 evaluation modes: clones with a short pod cycle seem to be less susceptible in the field than during artificial pod inoculations because the pathogenic exposure of their pods was shorter.