generations mean analysis

Grain yield, physiological and phenological traits in seven generations of maize using the generations mean analysis method under controlled conditions and, moderate and severe water deficit stress were studied. Evaluation of the generations drived from a cross between two inbred lines of maize including B73 and MO17, SC704 (as F1 generation), F2, BC1, BC2 and F3 using a randomized complete block design with 20 replications was conducted during two crop years of 2018-2019 at the Agricultural Research Station of University of Tabriz. The results of combined analysis of variance and mean comparisons of data under three different irrigation regimes showed that water deficit stress significantly reduced grain yield and physiological traits, and a significant increase in phenological traits. Generation mean analysis showed a high contribution of non-additive gene effects in the genetic control of the studied traits. This indicated that the necessity of selection in advanced segregating generations and the production of hybrid varieties in maize to take advantage of the dominance variance. Also, the significant contribution of additive gene effects in controlling the inheritance of the number of days to silk emergence indicated that selection in early segregating generations and inbred parents can be effective for breeding of this trait and taking advantage of additive variance. Based on the studied traits, inbred line MO17 and hybrid SC704 compared to other studied lines showed high tolerance to water deficit stress (from 5-6 leaf stage to silk emergence) and had the grain yield stability.

Increasing of yield is the most important objective of plant breeders in breeding programs. However, yield is a complex trait and includes several quantitative components. Its inheritance is polygenic, hence studying and improving the associated components to yield would promote yield. The objective of this study was to study the inheritance of quantitative traits in bread wheat using generations mean analysis (GMA). Sardari cultivar and inbred line 14, with different characteristics were crossed to develop the F1 generation. The F1 plants were selfed and backcrossed to both parents to produce F2 and backcross generations, respectively. All generations (F1, F2, BC1 and BC2) along with relevant parents were planted in field experimental station, Faculty of agricultural Tehran University, using a randomized complete block design (RCBD) with three replications. Generation mean analysis was performed using scaling test which asseses all generations simultaneously. The generations mean squares of the following traits: spike weight, plant height, number of kernel per spike, kernel weight per spike, 1000-kernel weight, awn length, spike length, awn status, spikelet compactness, kernel color, and number of tillers, were significant. The minimum number of genes controlling these traits, were 2, 2, 2, 2, 5, 1, 2, 4, 2, 2, 2 and 1, respectively. The average of broadsense and narrowsense heritabilities were 62% and 33%, respectively. Gene effects including mean, additive, dominance, epistasis effects as well as additive × additive, additive × dominance and dominance × dominance were observed for all traits. For awn length and number of tillers, additive and dominance effects and for other traits except awn status and glume color, the epistasis effects (specially additive × dominance and dominance × dominance) were determined as the most important effects in controlling the heritability of these traits. For spike weight, spike length, kernel weight per spike, awn length, plant height, spikelet compactness, and kernel color additive effect was more important than dominant effect. However, for number of kernel per spike dominant effect was more important than additive effect.