الفهرس 
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Abstract
The objectives of this study are to study and determine :- 1. The combinations which produce the best F1 hybrids. 2. The amounts of heterosis from the mid parents and the better parents for all traits. 3. The magnitudes of GCA and SCA. 4. The reciprocal crosses to determine the maternal effect. 5. The different types of genetic variances which include additive and non-additive variances. 6. The amounts of heritability in broad and narrow senses. 7. Finally, the correlation values between important traits of squash. Methods and Results. Five varieties were used and involved in a complete diallel crosses mating design to produce 10 F1 hybrids and 10 F1r reciprocal hybrids. These five varieties were: P1 Militte, P2 Caserta italiana, P3 Zucchini Grey, P4 Abobrinha redonda and P5 Eskandrani. These varieties have different origins where P1 and P5 from Egypt, P2 and P4 from Brazil and P3 from USA. The performance of the five parents, the 10 F1 hybrids and the 10 F1r reciprocal hybrids were variable. The P5 appeared to be the best parent for vegetative traits. For yield and fruit traits, once more P5 was not only the best parent but also better than most the hybrids for almost all traits. Heterosis from the better parent was not present for all vegetative traits where, many values were negative. The analysis of complete diallel crosses showed that both GCA, SCA and reciprocal were highly significant indicating their importance. The magnitude of GCA was always larger than SCA. The σ_A^2 variances were larger than σ_D^2, although, σ_D^2 variances were also present. These results were supported by absence of heterosis from the better parent. The hybrids including P4 as a male or a female parent would be consider as interspecific hybrids. The results indicated that the means of interspecific hybrids i.e. 1x4, 2x4, 3x4 and 4x5 and their reciprocals showed better performance from the other hybrids. Conclusion: The choice of the parents is of great importance to produce superior hybrids which would exceed the better parents. In this study, the parents were a result of breeding program and have a good performance and are used in commercial scale and therefore, they produce small amounts of heterosis from the better parent.