Abstract
The laboratory detached black pod test method has been suggested as the most economical and effective screening procedure to complement field black disease resistance selection. General combining ability and association between black pod disease incidence under field and laboratory conditions among 24 cocoa F1 families were investigated over a 7-year period. The 24 F1 families were derived by crossing three seed garden parental clones with eight GU clones as males in a 3 x 8 North Carolina II (NC II) mating design. The 24 families together with four standard varieties planted in a randomized complete-block design with four replicates of 25 trees per plot were monitored for percentage black pod disease incidence (PBDI). Selfed pods from the 24 NC families and four standard varieties were arranged in a completely randomized design with four replicates of five pods each in the laboratory and subsequently inoculated with Phytophthora megakarya isolates. Percentage detached pod disease incidence (PDDI) was determined after seven days of incubation. Family effects was significant (p < .01) for PBDI and PDDI, and the association between them was positively and moderately correlated (r = 0.71; p < .01). Broad-sense heritability was high but narrow-sense heritability was low for both traits. General combining ability effects of eight of the 11 parental clones and specific combining ability effects of 17 of the 24 crosses were consistent (positive or negative) for PDDI and PBDI. Results from the study indicate that there is a considerable association between both traits, and clones GU 125/C and GU 255/V and their corresponding crosses PA 150 × GU 255/V, T60/887 × GU 125/C, and PA7/808 × GU 255/V had favorable effects for resistance to black pod disease expression. It is concluded that the detached black pod test represents a suitable method to support the field selection of black pod-resistant cocoa varieties.
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