Genetic behaviour for plant capacity to produce chlorophyll in wheat (Triticum aestivum) under drought stress.

The study was conducted with the objective of identifying parents to be used in a breeding program to develop high chlorophyll varieties. Combining ability, heterosis and inheritance of chlorophyll content, including chlorophyll a, chlorophyll b and total chlorophyll (a+b), were investigated in bread wheat obtained from half-diallel crossings among eight parental lines.Cultivars with names of Irena/Babax//Pastor, S-78-11, Tajan, Chamran, Moghan3, Hamoon, Veery/Nacozari and Hirmand have different capacities to produce chlorophyll. Eight parental genotypes and their resulting 28 F1s were grown in three replications of randomised complete block design. Drought stress was performed with irrigation at 75% soil moisture depletion, the data collected were subjected to analysis of variance and combining abilities were carried out according to Griffing’s method 2, model 1. The study was conducted with the objective of identifying parents to be used in a breeding program to develop high chlorophyll varieties. General combining ability and specific combining ability effects were significant for traits’ chlorophyll content, chlorophyll a, chlorophyll b and total chlorophyll; however, non-additive gene effects were predominant over additive effects. The line Irena/Babax//Pastor transmitted high chlorophyll content based on general combining ability to progenies that were made with it. Broad-sense heritabilities were high and strict-sense heritabilities were low for the traits, confirming the importance of non-additive gene effects. This could bring definition of reduced selection efficiency for these mentioned traits

Genotype × environment interaction by AMMI and GGE biplot analysis in three consecutive generations of wheat (Triticum aestivum) under normal and drought stress conditions

Thirty six wheat genotypes derived from diallel crosses from F1 to F3 and their parents were evaluated in six different environments for the stability of performance. Performance was measured by seed yield per plant under drought and non-drought stress conditions. The experiment was conducted as a randomised complete block design with three replications in over one year. Additive main effects and multiplicative interaction (AMMI) and Genotype main effect and genotype x environment interaction (GGE) were employed in the evaluation of genotypes; AMMI analyses showed significant (P< 0.01) G × E, (genotype × environment interaction) with respect to plant seed yield. The AMMI stability value (ASV) revealed that cross number 14 (Irena × Veery) is stable. GGE-biplot models showed that the six environments used for the study belonged to two mega-environments. The GGE results also confirmed crosses number 11 (Irena × Chamran) and 17 (S-78-11 × Chamran) as the most stable, and recommended for the creation of hybrids. Based on environment 3 (F3 population, drought) with an inbreeding depression effect, hybrid number 17 (S-78-11 × Chamran) was identified as the best line due to its stability and high yield

Gene action for physiological parameters and use of relative water content (RWC) for selection of tolerant and high yield genotypes in F2 population of wheat

In order to identify parents suitable for use in a breeding program for the development of high quality and high yield varieties of bread wheat with drought tolerant genotypes, the combining ability and gene action for certain physiological traits were investigated in half-diallel crossings among eight parental lines. The cultivars investigated (Irena/Babax//Pastor, S-78-11, Tajan, Chamran, Moghan3, Hamoon, Veery/Nacozari and Hirmand) possess different tolerance levels to drought stress. Eight parental genotypes, and their resulting 28 F2 generations, were grown in a triplicate randomised complete block design.Drought stress and non-stress conditions were achieved through irrigation at 75% and 25% soil moisture depletion. Data were subjected to analysis of variance, combining abilities factor analysis and correlation analysis between drought tolerance indices and factor scores (according to Griffing's method 2, model 1). General combining ability and specific combining ability effects were significant for traits; however, non-additive gene effects were dominant over additive effects. The cultivar Chamran transmitted high relative water content (RWC) to its progeny, based on general combining ability. Broad-sense heritability was high and strict-sense heritability was low for the traits, confirming the importance of non-additive gene effects. The results of factor analysis revealed that three factors explained approximately 70% of total variation; these factors were strongly influenced by chlorophyll a and b, proline content, cell membrane stability, RWC and plant yield. Based on drought stress indices (STI and GMP), the cross Irena×Chamran was the most tolerant genotype. Correlation coefficients between two drought stress indices and the third factor from the factor analysis, which influenced RWC and plant yield, were positive and significant. Thus, RWC may be a good criterion for selection of tolerant genotypes with higher yields in breeding programmes

Genetic studies on physiological traits in wheat (Triticum aestivum L.) under normal and water stress conditions

Drought is a worldwide problem constraining global crop production and recent global climate change has made this situation more serious for the purpose of crop production, yield improvement and yield stability under water stress conditions.The development of drought tolerant varieties is the best option to overcome this problem. Eight contrasting genotypes (four drought tolerant genotypes Irena/Babax/ /Pastor, S-78-11, Chamran and Veery/Nacozari and of drought susceptible and semi susceptible varieties). Tajan, Moghan3, Hamoon and Hirmand were crossed in half diallel matings at the Agriculture and Natural Resources Research Centre of Sistan, Iran. F1 hybrids along with their parents were grown at the Experimental Farm of the Faculty of Agriculture, Universiti Putra, Malaysia under two conditions; irrigated and water deficit. Data were recorded for some physiological parameters and were analysed to understand the genetic mechanisms of these traits. Also, this study used molecular marker approaches in order to analyse the molecular genetics of drought resistance in segregated populations to identify quantitative trait loci (QTL) conferring resistance against drought stress in the F2 population derived from a cross of cultivar S-78-11 (tolerant) line and cultivar Tajan (susceptible) by Bulked Segregant Analysis (BSA). The results of the genetic analysis and graphical analysis revealed that the over dominant action of genes for height, chlorophyll a, b, (a+b), chlorophyll content, chlorophyll fluorescence, stomatal conductance, cell membrane stability, flag leaf area, proline content, relative water content (RWC) and plant grain yield remained unchanged under irrigated and rain-fed conditions. Sometimes the graphical analysis did not match the genetics components and this contradiction in the graphic representation and the components of variance appeared to be due to residual heterozygosity in the parents. Recessive and dominant gene controlled for chlorophyll a and RWC under irrigated and stress conditions and for Veery/Nacozari gene control from the dominant gene for chlorophyll content in the first generation changed to recessive gene control under the rainsfed conditions. Under special conditions (irrigated or stress) some traits like chlorophyll a and RWC have tended to be controlled by both recessive and dominant genes. It was also found that gene activity for many characters remained unchanged in different environments. The mean squares due to GCA and SCA were highly significant for all the traits in the F1, F2 and F3 generations with an exception of SCA for the chlorophyll content in first generation and GCA for flag leaf area. The general reduction of heterosis in the F2 generation was due to a decrease in heterozygosity through allelic fixation. Generally, predicted or expected inbreeding depression was higher than that observed for all traits, except for chlorophyll fluorescence. Cultivars S-78-11 and chamran was the best combiner for the reduction of stomatal conductance and grain yield under drought stress in three generations. In irrigated conditions, cross Veery/Nacozari×Hirmand had good performance of grain yield, but, in stress conditions, the crosses Irena×chamran and S-78-11×chamran had high values for the SCA. A total of 41 SSR primer pairs were used to screen the parents; five polymorphic primer pairs were identified which showed polymorphisms between parents, and three of them strongly amplified polymorphic bands among the F2 population. The continuous distribution of the RWC in the F2 population ranged from 62% to 86%. In this study, frequency distributions were examined to detect the extent of phenotypic variations occurring with high and low RWC. The linkage relationship between the SSR markers Xgwm182, Xgwm292, and Xgwm410 and the RWC as an indicator of drought tolerant genes was estimated using an F2 population derived from S78-11 × Tajan. The segregation ratio of the tolerant and the susceptible plants for tolerance to drought fitted the expected ratio of 1:2:1, indicating a codominant inheritance of this trait