Clonal selection in cacao based on early yield performance of grafted trees

An experiment with 45 Theobroma cacao L. clones grafted onto a common roots tock was established between September 1991 and November 1997 to determine the yield potential of trees selected from interclonal families. Scionwood of 40 promising trees selected from among 1,320 trees, representing five fa milies and three locations in Puerto Rico, were patch bud grafted onto the rootstock clone EET-400. Additionally, scionwood of five of the eight paren tal clones involved in the combination of the families was also grafted ont o the same rootstock. The 45 treatments were arranged in a randomized compl ete block design with six replications, each containing two experimental tr ees per replication. The trees reached full production in 1994, during the third growing year. Between 1994 and 1997 the mature pods were harvested, a nd the dry bean weight and pod index were determined. The means of the 40 g rafted selections were compared with the combined means of five parental cl ones or to the mean of their highest yielding parent (P less than or equal to 0.01). At the termination of the experiment in November 1997, only nine of the grafted clones significantly outyielded their parents, with a mean p roduction of 2,170 kg/ha/year of dry beans. This finding indicated that few er than 1% of the trees in the original five-family population were excepti onally superior yielders. Five of the nine superior yielding clones also ha d a significantly higher pod index. None of the 16 clones representing fami lies IMC-67 X SCA-12 and IMC-67 X UF-613 performed as superior yielders. We concluded that either one or both parents involved in these interclonal cr osses lack combining ability and may be excluded from cacao improvement pro grams. In addition, we found a direct relation between high pod index and s uperior dry bean weight in the progeny of family SCA-6 X EET-62.