In this study, we examined eight white inbred lines of maize and their F1 crosses under normal and drought stress conditions to estimate their combining ability for grain yield and associated traits. The results showed significant correlation (mean squares) of irrigation treatment with the studied traits. The effects of parents, crosses, and genotypes were all determined to be highly significant under both irrigation levels. Grain yield and other traits showed significant differences (mean squares) associated with both General combining ability (GCA) and Specific combining ability (SCA) under both irrigation regimes, demonstrating the importance of both additive and nonadditive genetic effects in the expression of performance traits. The parental line (P-86) had positive and highly significant GCA effects, as well as the crosses (P-17×P-96), (P-8×P-96), (P-8×P-171), (P-24×P-86), (P-86×P-96), (P-86×P-171), and (P-96×P-171) which then gave the highest specific combinations under both irrigation regimes for grain yield and some of the associated traits. The highest level of heterosis (heterobeltiosis) for grain yield was obtained in the crosses (P-8×P-96), (P-8×P-137), (P-8×P-171), (P-96×P137), and (P-96×P-171) under both irrigation regimes.

This experiment was implemented in the experimental farm of (Misr hytech seed co. Giza, Egypt) during winter growing seasons 2014 and 2015 to evaluate the inheritance of some cucumber vegetative and yielding traits using a complete diallel cross among five inbred lines. The results showed that the mean square of genotypes, parental inbred lines, crosses and parent vs crosses were significant for the studied traits. The hybrids P2xP4 and P2xP5 exhibited a useful heterosis relative to Mp and Bp for the fruit yield per plant and number of leaves per plant. The mean square of general and specific combining ability was significant for the studied traits. The higher GCA/SCA ratio than the unity of the studied traits indicating to the greatest role of the additive gene action in the expression of these traits. The inbred lines P1 and P 2 exhibited significant positive i g ˆ effects in the traits of number of fruit per plant and fruit yield per plant, so these inbred lines could be act as a good combiner for developing high yielding genotypes. The F1 hybrids P1xP3, P2xP4, P2xP5 and P4xP5 as well as the reciprocal hybrids P4xP1, P4xP2, P4xP3  and P5xP3 recorded a significant positive ij S ^  effect but the reciprocal hybrids recorded a significant rij effect. The results revealed to more than one hybrid distinct in some traits that could be utilized in the greenhouse cucumber cultivation and the future breeding programs.

Twenty one wheat hybrids and their seven parental genotypes were evaluated in the research farm of the Faculty of Agriculture, Ain shams University, Shoubra El-khema, Cairo, Egypt, in 2016/2017 growing season. The genetic analysis was conducted using Griffing (1956), Method 2, model 1).                 Significant differences among parent genotypes and their 21 crosses for all the studied traits (days to 50% heading, days to maturity, flag leaf area, plant height, number of spikes/ plant, spike length, number of spikelets/ spike, number of kernels/ spike, 1000-kernel weight and grain yield/ plant) were detected. This indicated that, variability exists among these populations may increase the chance appearance of good new combination that can be isolated in the succeeding generations. Parents versus crosses mean squares as an indication for average heterosis over all crosses were significant for all studied traits.                 Mean squares of general (GCA) and specific (SCA) combining abilities were significant for all studied traits except spike length trait for SCA which was insignificant. GCA/SCA ratios were more than unity for all studied traits, which indicating that the additive type of gene action is of great importance in the inheritance of these traits. Heterosis over the better parents showed that, the best hybrids were Gemmiza 9xGiza 168, Sakha 93x Giza, 168, Sakha 94x Jawahir-14, Sakha 94x Bob white, Giza 168xAcsad 925 and Jawahir-14x Bob white for grain yield/ plant trait and some of the other studied traits. The best general combiner parents were Sakha 94, Jawahir-14 and Bob white for grain yield/ plant trait and some of the other studied traits. The best SCA hybrids were Gemmiza 9x Sakha 93, Gemmiza 9x Giza 168, Sakha 93x Jawahir-14, Sakha 94xJawahir-14, Sakha 94x Acsad 925, Sakha 94xBob white, Giza 168x Jawahir-14, Giza 168x Acsad 925, Jawahir-14x Bob white and Acsad 925x Bob white for grain yield/ plant trait and some of the other studied traits. These result could be used in wheat breeding programs.

Thirty six entries of flax (Linum usitatissmum, L.) involving eight parental genotypes and their twenty eight hybrids were evaluated for straw yield and its related traits in the F1 during (2015/2016) and F2 populations during (2016/2017) under early (F2D1) and late (F2D2) sowing dates (two environments) in the Agricultural Research Station, Faculty of Agriculture, Ain Shams Univ., Shalakan, Kalubia Governorate. Mean squares due to genotypes, parents and crosses were highly significant for straw yield, plant height, technical stem length, fiber yield/plant, fiber percentage, fiber length and fiber fineness in the F1 and F2 generations (at early and late sowing dates), indicating that parental genotypes as well as their F1 and F2 generations exhibited reasonable degree of variability for all studied traits. Highly significant variations mean performance were found for parental genotypes and hybrids for straw yield/plant and its related traits in the F1, F2D1and F2D2, indicating presence of wide genetic variability among studied genotypes. The highest mean values were recorded under all studied environments, for straw yield/plant, fiber yield/plant and fiber fineness were found by S. 402/1 genotype, while Sakha 5 gave the highest mean values for plant height, technical stem length and fiber length.  General and specific combining ability mean squares were highly significant for all studied traits in F1, F2D1 and F2D2 with the exception of a few cases, indicating the importance of both additive and non-additive gene effects in the expression of  straw yield and its components. The additive effects were more important than non-additive effects under all studied environments for straw yield/plant (except at F2D2), plant height (except at F1), fiber percentage and fineness. On the other hand, the non- additive effects were more effective than additive effects for technical stem length, fiber yield/plant and fiber length. Results showed that the parents; Giza 11and Giza 12 for straw yield/plant, Sakha 5 for plant height and fiber length, Sakha 6 for fiber yield/plant, Jowhar  for fiber percentage and S. 402/1, Sakha 2, Giza 12 and Sakha 5 for fiber fineness, these parents appeared to be the best general combiners for these traits. Some of the crosses exhibited highly significant and positive SCA effects included high x high and high x low general combiner parents, suggesting that the breeding procedure which utilize both additive and non-additive genetic variances would be more useful for improvement of straw yield and its components of flax.

In this study, we examined eight white inbred lines of maize and their F1 crosses under normal and drought stress conditions to estimate their combining ability for grain yield and associated traits. The results showed significant correlation (mean squares) of irrigation treatment with the studied traits. The effects of parents, crosses, and genotypes were all determined to be highly significant under both irrigation levels. Grain yield and other traits showed significant differences (mean squares) associated with both General combining ability (GCA) and Specific combining ability (SCA) under both irrigation regimes, demonstrating the importance of both additive and nonadditive genetic effects in the expression of performance traits. The parental line (P-86) had positive and highly significant GCA effects, as well as the crosses (P-17×P-96), (P-8×P-96), (P-8×P-171), (P-24×P-86), (P-86×P-96), (P-86×P-171), and (P-96×P-171) which then gave the highest specific combinations under both irrigation regimes for grain yield and some of the associated traits. The highest level of heterosis (heterobeltiosis) for grain yield was obtained in the crosses (P-8×P-96), (P-8×P-137), (P-8×P-171), (P-96×P137), and (P-96×P-171) under both irrigation regimes.

Six bread wheat genotypes and their 15 F1 crosses were evaluated under two nitrogen fertilization levels (40 and 80 kg N/fed) to estimate combining ability for days to heading, plant height, spike length, number of spikes/plant, kernels number/spike, weight of 100-kernels and grain yield/plant during 2018/19 season. Results revealed that significant nitrogen levels (N) mean squares were detected for all studied characters. Mean squares due to genotypes (G), parents and crosses for the studied characters were significant at both nitrogen levels and their combined analyses. Also, G x N interaction was highly significant for the studied characters. The general and specific combining ability variances were found to be significant for all studied characters at both-N-levels and their combined analyses. GCA/SCA ratios were less than unity for all studied characters at both N-levels and their combined data. The behavior of gene action varied from nitrogen level to another where the interactions of GCA and SCA with nitrogen levels were significant for most studied characters. Sakha 93 was identified as the most useful source for increasing favorable alleles for grain yield/plant, kernels number/spike and weight of 100-kernels under N-stress conditions, while Giza 168 was the best combiner for earliness at the two N levels. Cross combinations; Sakha 93 x Sids 12 and Sakha 93 x Misr 1 gave the best SCA effects for grain yield/plant under N-stress conditions. Significant positive correlations were detected between means of parents and F1 crosses with their GCA and SCA effects for most studied characters under the two nitrogen levels, respectively

Seven cotton genotypes involving cvs. Giza 70, Giza, 77, Giza 86 and Giza 83 and the exotic varieties; Pima S7 and SeaIsland, as well as, the American Upland variety Tamcot C.E., were crossed in a diallel pattern, excluding reciprocals, in 2000 season to produce 21 F1 hybrids. Parents and F1­­'swere evaluated in 2001 season for eight economic traits. Mean squares due to genotypes were highly significant for all traits, revealing the presence of sufficient variability in the population. Significant desired negative mid and better parent heterosis were found for fiber-to-seed attachment force and days to flowering. Significant positive heterosis was also observed for yield and its components. The variances due to general combining ability (GCA) and specific combining ability, (SCA) were significant for all studied traits, indicating the importance of both additive and non additive gene action in the inheritance of these characters. The GCA/SCA ratio was found to be greater than unity, indicating predominance of additive and additive x additive types of gene action in the inheritance of these traits. Based on GCA effects, the Upland variety Tamcot C.E. proved to be the best general combiner for earliness, boll weight, seed index, seed cotton yield and lint cotton yield/ plant. Giza 83 seemed to be good combiner for fiber-to-seed attachment force, Giza 86 for lint percentage and Pima S7 for number of bolls per plant.