ASSESSMENT AND HERITABILITY OF PRODUCTIVITY AND TOLERANCE LEVEL TO PHYTOPHTHORA MEGAKARYA IN TWO HYBRID POPULATIONS OF THEOBROMA CACAO
P.F. Djocgoue, C. Simo, H.D. Mbouobda, T. Boudjeko, D.J. Nankeu, N.D. Omokolo
The cocoa tree (Theobroma cacao L.) is a cash crop cultivated in humid tropical regions. The commercialization of cocoa seeds constitutes a major source of income to farmers in the producing countries. Nevertheless, a major limiting factor to the culturing of this plant in Cameroon is black pod disease caused by Phytophthora megakarya. The vulnerability of T. cacao to P. megakarya was assessed in two hybrid populations (F79: ♀T79/467×♂SNK13; F13: ♀SNK13×♂T79/467) through the daily measurement of the necrotic lesion on the pods after artificial inoculation. The parental and progeny productivity was also assessed through measurements of the weight of 100 cocoa seeds. Principal Component Analysis (PCA) of the necrotic lesion on the pods taking into consideration the development of necrosis during time showed that 95.73% and 94.48% of the total variability expressed by axes 1 and 2 enables the classification of the different genotypes into 4 and 5 groups for F79 and F13 families, respectively. In addition, ANOVA results indicated that necrotic surfaces showed a significant effect of day after inoculation and genotype to all the progeny (P<0.001). Heritability of the two reciprocal crossings is high (0.81 for F79 and 0.91 for F13) and does not show a significant difference, suggesting the absence of maternal effects in the developmental character of necrosis. The hybrids F7902, F7909, F7917, F7921, F7925, F7928, F1304, F1307, F1309, F1314, F1318, F1323 and F1325 showed a higher productivity and less development of necrosis than those of the best parents. They can thus be considered as the best genotypes. These results suggest that a large scale distribution of these genotypes to farmers will permit a short term improvement of cocoa yield in Cameroon.