MANIFESTATION OF HETEROSIS AND GENETIC PARAMETERS ASSOCIATED WITH IT FOR SOME VEGETATIVE AND EARLINESS TRAITS IN SQUASH

The main objectives of this investigation were to determine the amounts of heterosis versus the mid-parents and the better parent, nature of gene action, heritability in both broad and narrow senses and correlation between each pair of traits. Four parental varieties ofsquash were crossed to obtain 12 F₁ hybrids according to a complete diallel crosses mating design.
The results revealed that the mean squares of genotypes which included four parental varieties and their hybrids were highly significant for all vegetative and earliness traits from the combined data. The results also cleared that mean values showed that no specific parent was superior for all studied traits. Generally, Eskandrani (P₁) was the best combiner for vein length (V.L.cm), number of leaves per plant (No.L./P.), fresh weight per plant (F.W./P.g) and dry weight per plant (D.W./P.g). Similarly, Zucchino mezza lung bianco (P₂) seemed to be the best combiner for leaf area (L.A.cm²) trait. The results also indicated that the parent P₂ was the best combiner for all earliness traits. On the other hand, the performance of most F₁,_1r hybrids were variable and the results cleared that no hybrid gave the best results for vegetative and earliness traits. The results revealed that heterosis over mid-parents indicated the presence of highly significant values for all studied traits except for fresh weight per plant (F.W./P.g). The estimates of heterosis versus better parent showed highly significant values for most studied traits. The results showed the importance of general and specific combining abilities. GCA were larger than their corresponding estimates of SCA for vegetative and earliness traits. Reciprocal effects (r) were significant for most studied traits from the combined data. Estimation of genetic parameters showed that additive genetic variance was very important for most studied traits. The inheritance of these traits was mostly governed by additive genetic variance rather than non-additive  and cytoplasmic genetic factors. In the same time, the estimates of heritability in broad sense were larger in magnitudes than their corresponding values in narrow sense.
Most pairs of traits exhibited positive genotypic and phenotypic correlation coefficients, such as: vein length (V.L.cm) with number of leaves per plant (No.L./P.), leaf area (L.A.cm²), fresh weight per plant (F.W./P.g) and dry weight per plant (D.W./P.g). Also, number of first female flowering node (No.1^stF.F.N) was significant correlated with date of first female flower (D.1^stF.F.) and date of first male flower (D.1^stM.F.). Therefore, plant breeders could design their programs, which make use of these advantages to select superior lines from the advanced segregating generations