Genetic variability and correlation studies in cocoa (Theobroma cacae L.)

Abstract

Investigation on the generic variability and correlation studies in cocoa were undertaken in the Department of Agricultural Botany, College of Horticulture, Vellanikkara during the period from July 1980 to August 1981 in a well established cocoa garden at Alpara in Trichur district, to elucidate information on the extent of variability and the degree of association existing among the 26 important plant, pod and bean characters, in a group of 135 cocoa tress, variety Forastero. Considerable variability was noted among all the characters of the sexually reproduced population of cocoa trees. Number of flowers per unit length on the trunk, number of pods per tree per year, weight of pod, volume of pod and wet weight of beans per pod showed maximum variability. Shell percentage and seed index manifested considerable variability among the bean characters. Phenotypic coefficient of variation (P.C.V.), genotypic coefficient of variation (G.C.V.) and heritability were estimated for 7 pod and bean characters. Both (P.C.V.) and (G.C.V.) were highest for attributes such as thickness of pod husk, number of beans per pod and weight of pod. Moderately high heritability was observed for weight of pod, thickness of pod husk and number of germinated beans. Volume of beans showed the lowest heritability. Yield from trees was found to be positively correlated with 6 of the characters studied, while number of germinated beans per pod and pod value were negatively correlated with yield. Out of the eight characters, pod value had the maximum contribution to yield. Number of pods per tree per year was found strongly associated with yield. Seed index and trunk girth also were positively and significantly correlated with yield. Phenotypic (rp) correlations among seven characters indicated that number of beans per pod was positively correlated with weight of pod. Positive correlations were also established between volume of beans and wet weight of beans per pod. Among the seven characters observed for genetypic (rg) correlations, wet weight of beans showed positive correlation with diameter of the pod and pod weight. Positive phenotypic as well as genotypic correlations were established in the case of wet weight of beans per pod with number of beans per pod and volume of beans. Number of beans per pod in turn, showed positive correlation with weight of pod at both levels. From the present studies it was evident that characters like diameter of pod, wet weight of beans per pod, number of beans per pod, number of germinated beans per pod, volume of pod, volume of bean, pod value, number of cushions on trunk, trunk girth, number of pods per tree per year and seed index have direct influence on the yield of cocoa. These traits can be considered while selecting cocoa trees for using in breeding programmes.