THEOBROMA-CACAO L - A GENETIC-LINKAGE MAP AND QUANTITATIVE TRAIT LOCIANALYSIS

A genetic linkage map of Theobroma cacao (cocoa) has been constructed from 131 backcross trees derived from a cross between a single tree of the variety Catongo and an F1 tree from the cross of Catongo by Pound 12. The map comprises 138 markers: 104 RAPD loci, 32 RFLP loci and tw o morphologic loci. Ten linkage groups were found which cover 1068 cen timorgans (cM). Only six (4%) molecular-marker loci show a significant deviation from the expected 1:1 segregation ratio. The average distan ce between two adjacent markers is 8.3 cM. The final genome-size estim ates based on two-point linkage data ranged from 1078 to 1112 cM for t he cocoa genome. This backcross progeny segregates for two apparently single gene loci controlling (1) anthocyanidin synthesis (Anth) in see ds, leaves and flowers and (2) self-compatibility (Autoc). The Anth lo cus was found to be 25 cM from Autoc and two molecular markers co-segr egate with Anth. The genetic linkage map was used to localize QTLs for early flowering, trunk diameter, jorquette height and ovule number in the BC1 generation using both single-point ANOVA and interval mapping . A minimum number of 2-4 QTLs (P<0.01) involved in the genetic expres sion of the traits studied was detected. Coincident map locations of a QTL for jorquette height and trunk diameter suggests the possibility of pleiotropic effects in cocoa for these traits. The combined estimat ed effects of the different mapped QTLs explained between 11.2% and 25 .8% of the phenotypic variance observed in the BC1 population.