الفهرس 
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Abstract
The main objectives of this investigation were to determine the amounts of heterosis over the midparents and the better parent, genetic parameters, heritability in both broad and narrow senses, combining abilities and correlation for all traits under study on squash (Cucurbita pepo, L.) varieties. The genetic materials used in the present investigation included four parental varieties of squash. These parental varieties were: Eskandrani (P1), Zucchino mezza lung bianco (P2), White Bush Scallop (P3) and Zucchino nano verde di Milano (P4). In conclusion, The results showed that the estimates of heterosis versus midparents and better parent showed highly significance for most studied traits, the importance of general (GCA) and specific (SCA) combining abilities. (GCA) was larger than their corresponding estimates of (SCA) for most studied traits at both F1 and F1r hybrids for vegetative, earliness, yield and yield component traits. Estimation of genetic parameters showed that additive genetic variance was very important for most studied traits. The importance of additive and nonadditive genetic variance in addition cytoplasmic genetic factors were played the major role in the inheritance of these traits not because the nonadditive genetic variance including not only dominance but also epistasis. In the same time, the estimate of heritability in both broad and narrow senses. The estimates of heritability in broad sense were larger in magnitudes than their corresponding values in narrow sense. In addition, The results showed positive genotypic and phenotypic correlation among pairs of these traits in squash. Therefore, it seemed that selection for improving one or more of these traits would improve the others. Therefore vegetable breeders would design their programs to use the superior F1 hybrids with high yielding and more earlier to select superior inbred lines in the advanced segregating generations.