Effects of general and specific combining ability and interaction between them for double crosses in zucchini squash (Cucurbita pepo L.)

This study used six inbred lines of squash (Cucurbita pepo L.), which were introduced into a half-diallel crossing program to derive 15 single cross hybrids. According to Rawlings and Cockerham's method of deriving 45 double-cross hybrids, single-cross hybrids were introduced into a double-cross. They included them in various trial experiments and estimations of the general and specific combining ability and gene action of the traits studied. The results showed highly significant differences in the mean square deviations for the double-crosses in all the studied traits. Inbred lines 6, 4 and 1 showed the highest general combining ability with the desired direction on fruit diameter and plant yield, respectively. Also, the double cross hybrids of order S1x2, t(23)(..), t(2.)(6.) showed the highest effect of the specific combining ability to combine on plant yield. Therefore, the effects of the specific combining ability are more important than the effects of the general combining ability in most of the studied traits, including the plant yield, referring to the importance of the dominant genet action and the dominant × dominant in the inheritance of these traits. Keywords: Genetic, squash, half-diallel, combining ability, single cross, Doublecross, breeding plant, hybrids.