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Abstract

A pre-breeding programme was initiated at CRU in 1997 to accumulate genes for resistance to black pod disease (Phytophthora pod rot) of cacao. Promising accessions were selected from the International Cocoa Genebank, Trinidad (ICG,T), intercrossed and their progenies screened for resistance to Phytophthora using a leaf disc inoculation method. From 36 crosses established in 1998, 1010 seedlings were tested in three rounds of leaf inoculations for resistance to P. palmivora. Results showed significant differences in resistance to P. palmivora among progenies from the 36 crosses. Progeny distributions for most crosses showed the occurrence of useful transgressive segregates with higher levels of resistance than the parental clones. Narrow sense (h„.s.) and broad sense (hbs.) heritabilities were estimated at 0.33 and 0.51, respectively. Genetic gain (Gs) was estimated at 0.98 on the 0-5 resistance rating scale (selection intensity, 10% = 1.755, standard deviation = 1.092 and h (b.s.) = 0.51). The selected seedling population would therefore have an average genetic resistance level of 2.42 (mean of all progenies, 3.4 - 0.98 expected genetic gain) which is higher than the resistance level of SCA 6 (2.64), a resistant control in the experiments. Based on the result of the leaf test for resistance to Phytophthora, 101 resistant seedlings were selected and planted in the field for further observations. The enhanced population derived from this programme should provide a source of useful resistance genes to black pod disease of cacao.

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