Estudo comparativo das teorias sobre o controle genetico das incompatibilidades do cacaueiro (Theobroma cacao L.)

Abstract

Using cacao clones of known and unknowen genotypes and hybrids between them a comparison was made of 2 theories of genetic control of incompatibilities, one of Knight and Rogers, based on sporophitic control by multiple alleles S and the other by Cope, using as criterion, the fusion and non fusion of ovules and male gametes, also controlled by multiple alleles and 2 additional pairs of genes. The results obtained by Knight and Rogers method and analized by X exponent 2 test did not show statistical differences with the espected theoretical values, indicating a lot of agreement with this hypothesis, allowing the classification of self compatible and self incompatible groups. On this basis genotypes were proposed for the new clones. In the self compatible plants a new fact was observed, which is related with the appearance of individuals with degrees of self compatibility. Groups with 50 and 75 percent of settings were observed and presumibly other clones are 100 percent self compatable. If this fact is proved a tentative genetic explanation is proposed. The results obtained by Cop's methodology and analyzed by X exponent 2 test, gave in all cases, but one (SCA 6), highly statistical differences with the expected values. These were more different so with reciprocal crosses of clones and hybrids, difficulting any genetical interpretation, even with modifications of Cope's proposed genetic hypothesis. These discrepances can be due to several reasons, namely: differences in the criterion of judging fusion and non fusion of ovules influence of differences of environmental factors on the physiology of the trees that could affect fusion and non fusion, and also the time of collecting the pollinated flowers could be different for the conditions of this study.