الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 134 |  |  |
| | | from | 134 | | |
Abstract
This study was carried out to help with the development of efficient breeding strategies for producing and improving hybrids of summer squash, suitable for Egyptian cultivation, which may replace the imported ones through: 1- Assessment of molecular and phenotypic diversity among some inbred lines of summer squash. These lines were Lungo di toscan (P1), S26 (P2), S24 (P3), CGN11916 (P4), PI/512788 (P5) and Eskandrani (P6). 2- Assessment of the heterosis, genetic parameters, combining ability and heritability of these inbred lines and their hybrids in a partial diallel analysis. 3- Assessment of the correlation relationships between genetic distances and estimated heterosis for hybrids obtained from crosses of these inbred lines. • The field experiments were carried out in Sakha Horticulture Research Station, Kafr Elsheikh Governorate, during summer season of 2013 to obtain 15 crosses produced through 6x6 half diallel mating system, these genotypes (six parents and its 15 F1 hybrids), were evaluated in the summer season of 2014. • Molecular assessment of the inbred lines was carried out using two molecular marker tequniques (RAPD and ISSR) and the most important results were the following: - Five RAPD and five ISSR primers succeeded in generating scorable and polymorphic amplicons that could be reliable to assess molecular diversity. - RAPD and ISSR techniques revealed 88.1 and 80.5 % polymorphism, as well as 5.00 and 3.4 resolving power (Rp), respectively. - Therefore, the RAPD technique was better than the ISSR technique in assessed molecular diversity and discrimination capacity among the six studied inbred lines. While, the ISSR technique was better than the RAPD technique in showing the unique molecular markers (21 for ISSRs and 9 for RAPDs). • Phenotypic distances (PD) were estimated using data of 12 economical phenotypic traits for the phenotypic diversity assessment among the six inbred lines. The types of these traits were vegetative, flowering, yield and fruit quality traits. • Cluster analysis based on MD and PD revealed that the studied inbred lines could be divided into two main groups (A and B). This indicated the possibility of obtaining hybrid vigours from hybridization between any inbred line from group A and any inbred line from group B. • Insignificant positive correlations among all types of MD (based on RAPD, ISSRs and their combined data) and PD were detected with values 0.045, 0.173 and 0.121, respectively. where the MD based on ISSRs was most positive in correlation value with PD. • Except for P6 which gave significant desirable value in two traits (number of fruits and yield per plant), each of the other five strains gave a significant desirable value in one trait. Thus, the number of traits that gave significant desirable value in all studied inbred lines were seven traits (N.B./P., S.R., S.L., F.W., N.L./P., Y./P. and N.F./P.). These traits could be linked with 11 negative and 19 positive unique markers, 21 out of them were generated by the ISSR technique. • Therefore, and through further studies, one or more of these unique markers could be used as markers assisted selection for any of those seven traits in the studied inbred lines. • The analysis of variances revealed significant mean squares values of all sources of variance (genotypes, parents, hybrids and parents vs. hybrids) for all studied traits, except mean squares valuesof parents vs. hybrids for F.W. and F.D. traits. Indicating the wide diversity between the genotypes used in this study. • The mean performance results of six parents and their 15 F1 hybrids showed that there was no specific parent revealed superior performance for all traits. Also, indicated that the presence of significant differences for many studied traits when the hybrids were compared with their parents or other parents. • A GCA/SCA ratio with a value greater than one was detected for S.L., N.B/P., N.L./P., S.R., D.O.F., F.W., F.L. and Sh.I. traits. This revealed that the additive genetic effects were more important and played a major role in the inheritance of these traits, indicating that selection would be a successful method for improving these traits. • On the contrary, the other traits (L.A., N.F./P., Y./P. and F.D.) revealed a GCA/SCA ratio with a value lower than one. This indicated that the non-additive genetic effects were more important and played a major role in the inheritance of these traits. Thus, hybridization would be a successful method for improving these traits. • For GCA effects, the results revealed that the parental inbred line P1 was the best combiner for N.B/P. and Sh.I. traits. While, P3 was the best combiner for L.A., D.O.F. and N.F./P traits. Also, P4 was the good combiner for S.R., F.W. and Y./P. Moreover, the parental lines P2, P5 and P6 were the best combiners for F.L.; N.L./P. and S.L. traits, respectively. • The results of SCA effects revealed that the hybrid between P2 × P4 had the highest positive SCA effects for L.A.; S.R. and N.F./P traits. Moreover, the hybrid between P1×P3 had the highest positive SCA effects for the F.W. trait and the highest negative SCA effects for the F.L trait.While the hybrids (P1×P2), (P1×P3), (P1×P5), (P1×P6), (P4×P5) and (P4×P6) had the highest positive SCA effects for N.L./P., N.B/P., Sh.I., Y./P. and S.R traits, respectively. On the other hand, the hybrids (P2 × P3),(P2 × P5) and (P3 × P4) had the highest negative SCA effects for D.O.F., S.L. and F.D. traits. • The estimates of heritability in broad sense (h2b.s.%) were larger in magnitudes than their corresponding values in narrow sense (h2n.s.%) for all studied traits. • Estimates of narrow sense heritability (h2 n.s.%) were found to be high for the D.O.F. trait (78.33%), and moderate for F.L. (57.98%) traits, reflecting the greatest role of additive gene effects in the inheritance of these traits. On the other hand, S.L., N.B/P., N.L./P., L.A., S.R., F.W., N.F./P., Y./P., Sh.I. and F.D. traits showed low (h2 n.s.%) values were 21.00, 34.78, 25.13, 18.33, 30.69, 36.63, 18.85, 16.93. 38.80 and 7.58 %, respectively. Indicating the predominant of non-additive gene effects in the inheritance of these traits. • The genetic parameter estimates revealed that the non-additive variance was higher than the additive variance for all studied traits except for D.O.F. and F.L. traits.This indicated that the non-additive genetic effects were played a major role in the inheritance of these traits. Therefore, hybridization would be a successful method for improving these traits. In contrast, for D.O.F. and F.L. traits, the non-additive genetic effects were played a major role in the inheritance of these traits. Therefore, selection would be a successful method for improving these two traits. • The estimates of heterosis detected that eight hybrids (P1 × P2, P1 × P3, P1 × P5, P2 × P3, P2 × P4, P2 × P5, P4 × P5, and P4 × P6) recorded the maximum significant desirable heterosis values over mid-parent for all studied traits. While eight hybrids (P1 × P3, P2 × P3, P2 × P4, P2 × P5, P3 × P4, P3 × P6, P4 × P5 and P4 × sP6) recorded the maximum significant desirable heterosis values over better parent for all studied traits except for the Sh.I. trait. • Poor correlation relationships among the two types of genetic distances with F1 heterosis for most traits were found. This requires evaluating genetic diversity for parent inbred lines in the breeding programs at more than location and under different climatic conditions. In conclusion, molecular and phenotypic assessment succeded in estimating genetic diversity. where a clear molecular and phenotypic diversity was detected among all studied inbred lines. RAPD technique was better than the ISSR technique in evaluating molecular diversity and discrimination capacity among studied inbred lines. But the ISSR technique was better than the RAPD technique in showing unique markers that may be associated with desirable performance in some of the studied traits. Therefore, and through further studies, one or more of these unique markers could be used as markers assisted selection for any of those traits in the studied inbred lines. Therefore, and depending on the presence of this genetic diversity among all studied inbred lines, most obtained hybrids were expected to show significant desirable values for the two types of heterosis for most studied traits, this is what happened. Moreover, most hybrids revealed a high specific combing ability for all traits. Also, the nature of gene action for each studied trait was determined, which helped to detect the suitable breeding method for improving each trait. So, this study recommends the breeder of squash for used the distinct hybrids obtained from this study to improve those economic traits through the suitable breeding method for each trait.