Toward The Identification Of Candidate Genes Involved In Black Pod Disease Resistance In Theobroma cacao L.

Black Pod (Phytophthora sp.) has a devastating effect on the worldwide cacao (Theobroma cacao) yield and incorporating resistance into production fields has been an ongoing effort of breeding programs.  Previous meta-QTL analysis of genetic maps created with a variety of molecular markers identified 13 consensus QTLs.  The resolution of these QTLs suffered from being associated with genetic maps with limited numbers of molecular markers.  Recently, three mapping populations were genotyped with a total of 6000 SNP markers.  Reciprocal crosses were made from ‘K82’ (resistant) and ‘KA2-101’ (susceptible), the resulting progeny were found to segregate for Black Pod resistance, and saturated genetic SNP maps were generated.  The forward cross ('K82' x 'KA2-101') consists of 215 individual trees and  2545 SNP markers, while the reverse cross ('KA2-101' x 'K82') has 110 individual trees and  2546 SNP markers.  Field-based pod rot phenotype data was collected on these populations over two years.  QTL analysis for Black Pod resistance is performed and compared to previously identified consensus QTLs.  Furthermore, candidate genes within identified QTLs will be investigated,and an association between resistance and parental haplotypes will be explored.  The identification of QTLs with a saturated genetic map, and the identification of genes potentially involved in Black Pod resistance will help breeding programs and may ultimately reduce global cacao losses.