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

Abstract

An experiment with 45 Theobroma cacao L. clones grafted onto a common rootstock 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 families and three locations "m Puerto Rico, were patch bud grafted onto the rootstock clone EET-400. Additionally, scionwood of five of the eight parental clones involved in the combination of the families was also grafted onto the same rootstock. The 45 treatments were arranged in a randomized complete block design with six replications, each containing two experimental trees per replication. The trees reached full production in 1994, during the third growing year. Between 1994 and 1997 the mature pods were harvested, and the dry bean weight and pod index were determined. The means of the 40 grafted selections were compared with the combined means of five parental clones or to the mean of their highest yielding parent (P < 0.01). At the termination of the experiment in November 1997, only nine of the grafted clones significantly outyielded their parents, with a mean production of 2,170 kg/ha/year of dry beans. This finding indicated that fewer than 1% of the trees in the original five-family population were exceptionally superior yielders. Five of the nine superior yielding clones also had a significantly higher pod index. None of the 16 clones representing families 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 crosses lack combining ability and may be excluded from cacao improvement programs, in addition, we found a direct relation between high pod index and superior dry bean weight in the progeny of family SCA-6 x EET-62.