Combining ability analysis of Cucurbita moschata D. in Côte d'Ivoire and classification of promising lines based on their gca effects.

Abstract

Cucurbita moschata varieties grown in Africa have very low yield. They have been neglected, and totally ignored in agricultural research programs. However, interest in their fruits, seeds, flowers and leaves is growing nowadays due to their nutritional and medicinal potentials. That growing interest has prompted plant breeders and agronomists to develop research programs for their improvement. A complete diallel cross analysis of four parental lines, Long, Zouan-H, Oval, and Soubre and their twelve F1 hybrids, was carried out in a farming environment at the University Nangui Abrogoua, Abidjan, Côte d'Ivoire. The four parental lines and the F1 hybrids were evaluated for their general performances, combining abilities, potency ratio and heterosis effects. The investigated traits included plant height, and eleven fruit- and seed-related characters. The analysis of variance showed significant differences for all traits studied. In addition, the diallel model yielded highly significant gca effects of the female parents. The gca effects of the male parents were significant for all traits except plant height, length of the fruit, width of the fruit and length of the seed. Highly significant sca effects were observed in the crosses for all the traits. Strong maternal effects were observed for the weight and diameter of the fruit, weight of the pulp, number of seeds per fruit, weight of the fresh seeds and 100-seed weight. The general predictive ratio approached the value 1 for all the traits except weight of the fresh seed and width of the dry seed. Most of the characters under this study are predominantly determined by the effects of additive genes. But, weight of the fresh seed and width of the dry seed may be controlled by non-additive genes. Mid-parent heterosis was significant for all measured traits in the crosses, except the length of the fruit. And better-parent heterosis was significant for all traits except plant height, number of fruits per plant and length of the fruit. Gene expression is described by a super-dominance for many traits, and partial dominance for some other traits in all twelve F1 hybrids. Classification of the parental lines based on the effects of their general combining ability grouped the Soubre lines as promising contributors to fruit yield. The parental lines Long and Oval formed another group likely on the basis of the small size of their fruits, the small pulps, the smaller number of fruits per plant and the large number of seeds per fruit. However, Long would be a candidate parent for the development of cultivars with longer vegetative growth. The parental line Zouan-H formed the third group and it was mostly characterized by its large number of seeds per fruit and relatively large fruits.