Mating system in a natural population of Theobroma grandiflorum

The aim of this research was to study the mating system of a natural population of Theobroma grandiflorum (cupuassu) from Nova Ipixuna, Pará state, using microsatellite markers. Eight polymorphic microsatellite loci were analyzed in eight families, each represented by 10 six-month old seedlings derived from open-pollinated pods. The estimation for the multilocus outcrossing rate ($tm = 1.0) and individual outcrossing rate ($t = 1.0) for this population suggests that T. grandiflorum may be a perfect outbreeding (allogamous) species. Likewise, for the studied population the estimate for single locus outcrossing rate ($ts) was elevated (0.946), but lower than $tm, confirming the likely outcrossing character of the species and suggesting the occurrence of 5.4 % biparental inbreeding rate ($tm- $ts). The estimation of genetic divergence ($FST) between allelic frequencies in ovules and pollen revealed a deviation from random mating in 75 % of the evaluated loci. Likewise, the estimate of correlation of paternity ($rp = 0.930) and the mean coefficient of co-ancestrality within families ($θxy = 0.501) indicated that the outcrossings were predominantly correlated, and the offspring were full-sibs. These results suggested that for this particular population of T. grandiflorum, the sampling strategy for genetic conservation and breeding should adopt specific models for families derived from correlated outcrossing (full-sibs) and not the ones usually adopted in classic outcrossing species breeding programs (half-sibs)