Breeding cycle of fifth generation inbred of cocoa and performance analysis of progenies over generations

Cocoa (Theobroma cacao L), the only source of chocolate has a highly complex genetic structure. Kerala Agricultural University (KAU) started inbreeding programme since 1987 with the objective of producing homozygous inbreds for use as parents for hybridization programme. Inbred crosses between two distinct genotypes are expected to produce exceptionally high vigour in F₁ generation. Use of homozygous inbreds as parents eliminates the problem of high variability among the progenies when heterozygous parents are produced.

World's first reported fifth inbreeding generation (S₅) of GII 7.4 accession was field established at KAU during 2006. Seedlings established in the field in successive generation were very less because of high level of abnormalities expressed in the nursery. But when performance of field established inbreds over generations was analyzed, there was not much significant inbreeding depression when compared to preceding generation. This might be due to the presence of characters controlled by additive genes, only vigorous inbreds were field established and ancestral parents of GII 7.4 may be adapted to self pollination. The results of some former studies indicated that different genotypes of cocoa responded in different way to inbreeding depression. Hence, non-expression of inbreeding depression by a single genotype may not rule out the possibility of using cocoa inbreds in commercial hybrid production. More over hybrids produced from two diverse inbreds will have an added advantage of combination of only superior alleles from both genetically divergent parents.