Evolution of Grain Yield and its Components Relationships in Bread Wheat Genotypes under Full Irrigation and Terminal Water Stress Conditions Using Multivariate Statistical Analysis

To study relationships between effective traits on wheat grain yield، the varieties Zarrin and Alvand، and some promising lines i. e. C-81-4، C-81-10، C-81-14 and C-82-12 were investigated at three sowing dates including 10 October، 1 November and 21 November. The experiment was carried out using strip plot in RCBD with three replications under two different water conditions including full-irrigation and terminal water stress at Miyandoab Agricultural Research Station in 2005-06 and 2006-07 cropping seasons. The results showed that under both full irrigation and terminal water stress conditions، grain yield had positive and significant correlation with days to heading، days to maturity، plant height، number of spikes/m2 and 1000 grain weight. Stepwise regression analysis revealed that 83 percent of yield variation under non-stressed conditions could be determined by days to maturity and number of spikes/m2 (R2 = 83%) whereas these traits explained 87% of yield variation under stress conditions (R2= 87%). Path analysis indicated that number of spikes/m2 and days to maturity had the greatest positive direct and indirect effect on grain yield، under both conditions. The results of factor analysis under non-stressed condition showed that three factors explained 77% of total variation; these factors were called grain yield components، grain characteristics and plant phonology. Under non-stressed condition two factors (that were called grain yield and phenology، and plant morphology) explained 88% of total variation. Cluster analysis through ward method، classified days to maturity and number of spikes/m2 in the same cluster where the grain yield was put under both conditions. It was concluded that under different sowing dates، selection based on days to maturity and number spikes/m2 could indirectly led to higher yield under both normal and water stress conditions.