الفهرس 
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Abstract
Genetical studies on production of squash hybrids (Cucurbita pepo L.) The breeding of the economic traits in summer squash is strongly influenced by the genetic determination and depend on source of genetic variation in population. This experiment was carried out at Qaha Research Farm for Vegetable Crops, Hort. Res. Inst., Agric. Res. Center, Qaluabia Governorate, Egypt; during 2017 to 2019 consecutive seasons. Four evaluated genotypes were acceptable for most horticultural traits had chosen from the eight stable genotypes to self-pollination as well as it crossed in a half diallel mating design. The experimental was designed in randomized complete block design with three replicates. Each replicate consisted of 13 plots which included four parental genotypes and their six F1 hybrids, as well as three commercial check cultivars. Then, all genotypes evaluated in to summer seasons of 2018 and 2019 for vegetative, flowering, fruit and yield traits. 5.1 The following measurements were recorded for the individual plants: 1- Vegetative traits: Stem length (cm), internode length (cm) and branches number/plant. 2- Flowering traits: Number of male flowers per plant, number of female flowers per plant, sex ratio and days to first female flower anthesis. 3- Fruit traits: Fruit length (cm), fruit diameter (cm), fruit shape index and average fruit weight (g), 4- Fruit yield and yield component traits: Fruits number/plant, fruits weight/plant (kg) and total fruits weight per fed. (ton). 5.2 The results can be summarized as follows: 5.2.1 Analysis of variance The results of the analysis of variance and tests of significant on the mean squares revealed that the genotype mean squares were highly significant for all studied traits in both seasons, except for branches number/plant and days to first female flowering anthesis traits had significant values in the 2nd season. These results indicate the presence of real differences among all genotypes. 5.2.2 Mean performance of genotypes 5.2.2.1 Parents (pure lines) The results of mean values showed that no parental line was superior for all studied traits. Generally, the parental P3 had the highest mean values for stem length, internode length, branches number/plant, fruits number/plant, fruits weight/plant and total fruits yield per fed., as well as its exhibited the lowest mean value for days to first female flowering anthesis (desirable) in both seasons. Moreover, the parent P4 had the highest values for average fruit weight, fruit diameter and number of female flowers per plant in the both seasons. Parent P2 exhibited the best values for number of male flowers per plant and it was the lowest for sex ratio (desirable) and the parent P1 had the high mean values for fruit length and fruit shape index in both seasons. 5.2.2.2 F1 hybrids The performance of most F1 hybrids were variable and the results revealed that there was no hybrid showing the best result for all studied traits. The two crosses P2xP3 and P1xP3 exhibited the lowest mean values for flowering traits (desirable) as days to first female flower anthesis and number of female flowers per plant and sex ratio, respectively. Also, the cross P1xP4 had the highest mean value for fruits number per plant. While, the cross P1xP2 showed high values for fruit length and fruit shape index. As well as, the cross P2xP4 had the highest mean values for fruit diameter and number of braches per plant. In the same way, the cross P3xP4 showed high mean value for stem length, internode length, number of male flowers per plant, average fruit weight, fruits weight per plant and total fruits weight per fed. in the both seasons. Likely, the three crosses P1xP2, P1xP4 and P3xP4 gave the best mean values over the commercial cultivars for fruits number/plant, sex ratio, fruit length, fruit shape index and fruits weight/plant traits. Therefore, the above new hybrids were superior and exceeded the commercial cultivars, indicating it could be recommended the importance production of new hybrids. 5.2.3 Heterosis The amount of heterosis relative to mid-parent and better parent were variable in significance which summarized as follow: The cross P1xP3 had the highest mean values of M.P heterosis for sex ratio, fruit diameter, fruit shape and average fruit weight. The cross P1xP4 had the best value of heterosis versus mid-parent for stem length, fruits number per plant, fruits weight per plant and total fruits yield per feddan. As well as, the cross P2xP3 for fruit length and number of days to first female flower. In addition, the cross P2xP4 for internode length and branches number/plant in both seasons. Regarding heterosis versus better parent the cross P1xP3 had the highest value of heterosis (HB.P%) for fruit diameter, fruit shape index, average fruit weight and sex ratio. As well as, the cross P1xP4 exhibited the highest value of heterosis relative to better parent for stem length, fruits number/plant, fruits weight/plant and total fruits weight per feddan. Also, the cross P2xP3 had best values of heterosis (HB.P%) for days to first female flower and fruit length, as well as the F1 hybrid P2xP4 for internode length and branches number/plant in the both seasons. 5.2.4 Combining ability analysis Tests of significance of the mean squares of combining ability analysis showed the importance of GCA and SCA effects for most studied traits. General combining ability was highly significant or significant for all studied traits, except for fruits number/plant in both seasons and sex ratio in the 2nd season was insignificant. Moreover, the means squares of SCA was not significant for internode length and days to first female flowering anhtesis in both seasons, as well as branches number/plant in the 2nd season. The calculated ratio GCA/SCA was more than unity for all traits except for fruit diameter, fruit shape index, fruits number/plant, fruits weight/plant and total fruits weight per fed., which indicated that the additive type of gene action was more important in the inheritance of all studied characters, except later controlled by non-additive gene action. 5.2.4.1 General combining ability effect for each line The results of GCA effects for each line indicated that lines differed in its effect and ability of combination. The parental P1 was a good general combiner in forming hybrids for fruit length and fruit shape index. The parent line P2 was found to be a good combiner in forming hybrids for low sex ratio. Moreover, the parental P3 was a good combiner in forming hybrids with low days to first female flower anthesis and the high value of internode length, branches number/plant, fruit diameter and fruits number per plant. On the other hand, the parental P4 with high value of average fruit weight, fruits weight per plant and total fruits weight per fed. in both seasons. 5.2.4.2 Specific combining ability effect for each cross The result of SCA effects (Sij) for each cross indicated that lines differed in its effect and ability of combination. The result revealed that the best specific combinations resulted from crossing good x good or poor x good general combiners. The best combination for most studied trait of F1 hybrids were P1xP2 for fruit shape index. The cross P1xP3 for average fruit weight and sex ratio. Also, the cross P1xP4 for fruit length and fruits number/plant. The cross P2xP3 for fruit length and days to first female flower anthesis. The cross P3xP4 for fruits weight/plant and total fruits weight per feddan. Likely the cross P2xP4 for internode length, branches number/plant and fruit diameter in both seasons. The absence of significant specific combining ability effect (Sij) would explain the absence of large amount of heterosis over better parent. It is known that high values of heterosis and the production of superior F1 hybrids depend mainly on the presence of large and significant sex effect. 5.2.5 Estimates of genetic parameters from the obtained results, non-additive genetic variance including dominance (2D) were most important source of genetic variance than additive genetic variance (2A) for most traits: days to first female flower anthesis, fruit length, fruit diameter, fruit shape index, average fruit weight, branches number/plant, fruits weight per plant and total fruits weight per fed. in the both seasons. 5.2.6 Estimates of heritability. The estimates of heritability in broad sense were generally larger than the corresponding estimates of heritability in narrow sense for all studied traits, except for sex ratio less heritability in narrow sense, which mean absence of dominance effect under this study condition. The broad and narrow sense heritability estimates for stem length and internode length, were high and closely which mean the importance of additive effect in the inheritance of these traits. On other hand, internode length and average fruit weight showed high value for broad sense heritability and medium values in narrow sense. These results indicate the influence of the environmental factors had non-additive type of gene action on the expression and inheritance of these characters. Finally, broad sense heritability for sex ratio, fruit diameter, fruits number/ plant, fruits weight/plant and total fruits weight per fed. high cleared that, low value of narrow sense heritability indicated the high involvement of the non-additive and environmental effects on the expression of these traits. CONCLUSION from the previous results, it could be concluded that the parental line P3 was the best for most studied traits, vegetative, flowering, fruit and yield traits. The performance of most F1 hybrids showed that the crosses P1xP3 and P2xP3 exhibited the best values for flowering traits. In the same way, the cross P1xP4 showed best value for fruit traits and fruits weight per plant and total fruits weight per fed. in the both seasons. The crosses P1xP2, P1xP4 and P3xP4 had better values over the commercial cultivars for fruits number/plant, sex ratio, fruit length, fruit shape index, fruits weight/plant and total fruits weight per feddan. Therefore, the above new hybrids were superior and exceed the commercial cultivars, indicating it could be recommended the importance production of new hybrids. Also, the performance of F1 hybrids showed amount of heterosis relative to mid-parent as well as better parent. The importance of additive and non-additive genetic variance which contributed in the inheritance of the most studied traits. Regarding heritability in broad sense were larger than their narrow sense heritability for most studied traits, which cleared that squash breeders would design their programs for use the selection in the imported new lines of squash followed by self-breeding for individual plants to obtain homozygous lines. These results indicated that plant breeders should select the parents which yield superior F1 hybrids through hybridization. In view of the results of this investigation recommendation would be declared to use selection in the imported lines of squash followed by inbreeding to obtain inbred lines to use it as commercial cultivars or through selection programs in the segregated generation. Also, consider it as a source of genetic divergence for the summer squash breeder.