The present investigation aimed to determine genetic parameters and type of gene action controlling some agronomic traits of the two bread wheat crosses, Shandawel 1 × Gemmeiza 11 and Misr 1 × Giza 168 under normal 20 th Nov. and heat stress 20 th Dec. conditions, using six populations model (P 1 , P 2 , F 1 , F 2 , B C1 and B C2). Scaling test indicated the presence of non-allelic interactions for all studied traits except number of spikes/plant in cross 2 under normal conditions, number of grains/spike in cross1 under favorable conditions and in cross 2 under heat stress and grain yield/plant in cross 1 under normal conditions. The relative importance of additive and dominance effects varied for traits and crosses under normal and heat stress conditions. Dominance effects were generally greater than additive, except for days to heading in cross 2 under heat stress, plant height under normal conditions in cross 2 and biological yield in cross 1 under heat stress and in cross 2 under normal conditions, indicating that dominant genes playing major role in inheritance of these beside the additive one. Dominance × dominance gene interaction was higher in magnitude than additive × additive and additive × dominance in most traits, indicating that these traits greatly affected by dominance and non-allelic interactions. Therefore, it is advisable to delay selection to later generations with increased homozygosity. Positive highly significant heterosis over better parent values were observed for all studied traits, except for plant height in cross 2 under both sowing dates, number of grains/spike in cross 1 under heat stress and in cross 2 under both environments. Broad sense and narrow sense heritability and genetic advance ranged from moderate to high in most cases. Based on these results, these two crosses could be selected to produce high yielding lines under heat stress conditions.
The objectives of the present research were to study the direct selection response for grain yield plant -1 under normal and deficit irrigation conditions and estimate the correlated response of other studied traits. Two cycles of selection were practiced on a segregating populations of wheat cross (Sid 1× Misr 2) in the F 3 -F 5 generations. Selection was practiced separately under normal and deficit irrigation conditions. The genotypic variance was slightly less than the phenotypic variance under both environments and generally decreased from the base population (F 3 ) to the F 5 generation. Broad-sense heritability estimates for grain yield plant -1 after two cycles of selection were 65.66 and 59.95% under normal and deficit irrigation, respectively. The realized heritability under normal irrigation was 47.94 and 53.66% compared to 34.90 and 58.64% under deficit irrigation conditions after the first and second cycles of selection, respectively. The average observed gain for grain yield plant -1 from selection under normal and deficit irrigation groups, evaluated under normal irrigation were (13.92 and 15.48%) over the bulk sample and (9.27 and 10.78%) over the better parent, respectively. While, from selection under normal and deficit irrigation, evaluated under deficit irrigation were (16.87 and 20.08%) over the bulk sample and (15.44 and 18.61%) over the better parent, respectively. Drought susceptibility index (DSI) showed that six families selected under normal irrigation and five families selected under deficit irrigation were superior for drought tolerance and had high grain yield under deficit irrigation in F 5 generation. The antagonistic selection was better than the synergistic selection in changing the mean and decreasing the sensitivity.
The current investigation was conducted at Shandaweel Agric. Res. Station, Sohag governorate, Egypt during 2018/2019 to 2020/2021 seasons. Pedigree selection of grain yield plant -1 was practiced independently from the F 2 to F 4 generations under normal and late planting dates. Evaluation was under both planting dates in the F 4 generation. The phenotypic variance was slightly higher than the genotypic variance, and reduced from the F 2 to F 4 generation. Broad-sense heritability was 83.47 and 86.73% under normal planting compared to 88.22 and 89.03% under late planting after the first and second cycle of selection, respectively. The realized heritability was 37.75 and 40.63% under normal planting compared to 57.75 and 83.48% under late planting after cycle 1 and 2, respectively. The average observed gain of grain yield plant -1 after two cycles of pedigree selection was 12.59 and 25.33% from bulk sample and 7.45 and 2.69% from the better parent for normal planting selections, while it was 22.05 and 47.18% from bulk sample and 16.48 and 20.59% from the better parent for late planting selections, when the selected families were evaluated under normal and late planting conditions, respectively. The antagonistic selection increased the mean and decreased the sensitivity compared to the synergistic selection either evaluation was under normal or late planting conditions. Based on the path-coefficient analysis, number of spikes plant -1 had the greatest positive direct effect on grain yield plant -1 followed by number of kernels spikes -1 and 100-kernel weight in the base population and cycle two of selection under both planting dates.
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