ABSTRACT
The present article was carried out for four seasons to study the relative merits of pedigree selection for days to heading (DH) restricted by grain yield/plant (GY/P) under drought stress and normal irrigation environments to compare three cycles of selection started in the F2 to the F5 with one cycle started in the F4-generation, and to study the sensitivity of the selected families to environments, in addition to monitoring TaELF3 gene expression in bread wheat. The reduction % in DH in the F2 caused by drought stress was 5.1 compared to 2.8 and 3.29% for the two parents Sids4 and Giza164; respectively. The phenotypic (PCV)and genotypic(GCV) coefficients of variability decreased from 5.15 and 4.08% in the F2 to 1.72 and 1.64% after cycle3 under drought stress, and from 6.14 and 2.1% in the F2 to 3.73 and 3.71% after cycle3 under normal irrigation; respectively. The realized heritability increased from 68.15% in cycle1 to 70.5% in cycle3 under drought stress, and from 80.45 to 88.40% under normal irrigation for the respective cycles. The observed genetic gain (OG) in DH of C3 drought selected families was -5.31 and -5.06% (P≤0.01) of the bulk sample, compared to -7.29 and -6.24% for normal irrigation selected families, when evaluation was practiced under drought stress and normal irrigation; respectively. Realized heritability of DH under normal irrigation (antagonistic selection) increased from 68.15 % in cycle1 to 70.5% in cycle3 under drought stress, and from 80.45 to 88.40% under normal irrigation for the respective cycles. The observed genetic grain (OG) in DH of C3 drought selected families was -5.31 and -5.065 (P≤0.01) of the bulk sample, compared to -7.29 and -6.24% for normal irrigated selected families, when evaluation practiced under drought stress and normal irrigation; respectively. Selection for DH under normal irrigation (antagonistic selection) was better than under drought stress (synergistic selection). The results indicated that one cycle of selection for DH started in F4 was equal or better than three cycles started in F2, especially under normal irrigation. The results suggested delaying selection for DH to the F4 or F5 till the recombinants reached acceptable level of homozygosity to save efforts and expenses. The correlated gain in GY/P after three cycles under drought stress was 10.92 and 10.0%, and was 14.94 and 12.36% after one cycle from the F4, while it was 22.18 and 21.20% after three cycles under normal irrigation, and 24.97 and 23.97% after one cycle from F4, from the bulk sample and the better parent; respectively. The other correlated gains were discussed. The relative merits of selection for DH indicated that selection for DH under normal irrigation (antagonistic selection) was better than selection under drought stress (synergistic selection) in changing the mean. qRT-PCR was used to test the expression levels of the TaELF3 gene, responsible for the early flowering in T. aestivum, under both normal irrigation and drought stress conditions, confirming that drought stress enhanced the expression TaELF3 gene and reduced the required days to heading.