[Genetic analysis of segregating generation for yield and its components in hybrids of yellow maize (Zea mays L.).]

The four single hybrids were selected from 28 single crosses resulted from the half diallel cross among 8 inbred lines at maize department in the growing season of 2008. In the growing season of 2009 the F1 populations of each hybrids were grown in 5 rows to get the F2 population of each hybrid by inbreeding each plants in the rows. And formation new F1 seeds and copiously the seeds of parents lines. In the growing season of 2010 the F2 populations of each hybrids were grown in 10 rows to get the F3 population of each hybrid by inbreeding each plants in the rows. The five populations of each hybrids (P1, P2, F1, F2, F3) were grown in the growing season of 2011 in two separate experiments, Each one contained three replications using randomized block design. Each replication consisted four rows of F1, P1, P2 and 13 rows of F2 population for each hybrid and 8 rows of F3 populations. The row length was 6 m with a spacing of 70 cm between rows and 25 cm between plants in the row. The first experiment was without stress so it was irrigated every 10±2 days regularly so the total number of irrigations was 10, while in the stress experiment (mild stress) was irrigated every (17±2) through the growing season (two irrigations for planting and germination, two irrigations at the vegetative stage and three irrigations at the reproductive stage), so the water stress was done through the vegetative stages (V10, V14, V16,), and through the reproductive stage (R4). The data was recorded on 20 individuals per replication of P1, P2, F1 and on 40 individuals of F2 populations for each replicate and each hybrid. The results of the analysis of variance and the other genetic parameters indicated: There was significant variance among the five populations for studied traits for four hybrids under two treatments, and among the individuals of F2, F3 populations. The variance in non segregation population (P1, P2, F1) were non significant. Most of traits decreased under stress conditions, and the highest values were 17% for yield per plant, 15% for plant and ear height and 12% for 100 grains weight. The inbred lines (IL.275-06), (IL.362-06), (IL.363-06) get the best means of yield per plant under two conditions. The single hybrids (IL.275-06 x IL.362-06), (IL.363-06 x IL.459-06) get the best means of yield per plant under two conditions. The F2 population of the hybrid (IL.275-06 x IL.362-06) get the best yield per plant among the F2 populations under two conditions. The best desirable heterosis percentage for yield per plant were 199.34%, 281.49% relative to mid parents for the hybrid (IL.363-06 × IL.459-06) under non stress and stress treatments respectively, and 145.33%, 191.47% for the hybrid (IL.363-06 × IL.459-06) relative to the better parents under two conditions respectively. The high value of the inbreeding depression was 37.54, 35.82 for the hybrid (IL.275-06 × IL.362-06) under non stress and stress conditions respectively. Results of generation means and the gene action indicated the importance of dominance and epistasis in the inheritance of most studied traits under two conditions. The value of phenotypic and genotypic variability were closely denote the importance of gene action in the behavior of traits. the best values of broad sense heritability for yield per plant were 0.86, 0.80 for (IL.363-06 × IL.459-06) under non stress and stress conditions respectively, while the high values of narrow sense heritability and genetic advance were 0.39, 13.67 respectively for hybrid (IL. 375-06 × IL.256-06) under the first condition, and 0.41, 10.59 respectively for the hybrid (IL.363-06 × IL.459-06) under the stress condition. The phenotypic correlation analysis under non stress condition indicated positive and significant correlation between yield per plant and ear length, ear diameter, plant height, grain content's of starch, days to silking, 100 grains weight and number of leaves per plant. Path analysis showed ear length, 100 grains weight, ear diameter, plant and ear height had highest effects on grain yield under non stress condition. The phenotypic correlation analysis under stress treatment showed positive and significant correlation between yield per plant and plant height, ear length, ear height, 100 grains weight, ear diameter, grains content's of oil, leaves per plant and branches per tassel. Path analysis indicated that plant height, ear height, 100 grains weight, ear length and ear diameter were the important selection traits under stress in the studied material. According to drought stress indexes, the analysis of variances indicated significant differences among genotypes for all drought indices. The lines (IL.275-06), (IL.256-06), achieved the best values of yield per plant under both normal and stress conditions. Therefore these lines can be used through diallel cross to get new single hybrids of maize with high yield under non stress conditions and good tolerance under stress conditions. The single hybrid) IL.275-06 x IL.362-06) get the best tolerance under stress conditions, so it had economic value under two conditions, the segregation generation of this hybrid) IL.275-06 x IL.362-06) will help to improve yield and get new inbred lines of maize under stress conditions. The phenotypic correlation analysis among drought stress indexes indicated that yield under non stress and stress conditions were positively and significantly correlated with Geometric mean productivity, Harmonic mean and Drought resistance index indicated that selection for these indices can help breeder to improve yield under stress and non stress conditions.