Abstract:
Five Upper Amazons cocoa clones, namely NA33, PA150, PA7, SCA6
and SCA9 were selected for this study. The objective of the
study was to ascertain the resistance level of the resistance
to the CSSV disease.
Test parents were clonally multiplied and inoculated and the
expressed leaf symptoms studied. The difference observed in the
parents were used to initiate hybridization. Mentor pollen
technique was used to induce self-fertilization.
Clonal multiplication was done by budding and mealybugs
(P. njalensis) was used for the inoculation. Herrania balaensis
was also used as mentor pollen to induce self-fertilization in
self incompatible clones.
Diallel crosses show that all genetic parameters studied are
under polygenic control and all show additive effect. Reistance
genes were found to be recessive to susceptibility. The order
of resistance among the five clones was NA33 > PA150 > PA7 >
SCA6 > SCA9. Comparative studies of the progenies of these
crosses revealed that crosses between NA33 as female parent
with PA7 and PA150 as pollen parent scored high percentages of
resistance. Crosses between PA7 and PA150 also recorded high
percentages of resistance. NA33 had higher general combining
ability than the rest.
The expressed leaf symptoms also vary from one clone to the
other. The highly resistant ones either showed no symptoms or
expressed symptoms associated with mild strain of the virus,
while the susceptible ones showed some amount of virulent
strain symptoms in addition to the mild ones.
The General Combining Ability (GCA) and Specific Combining
Ability (SCA) values for resistance were not significant but
the GCA mean square was higher in the analysis than the SCA.
The narrow sense heritability was high (79%),'