Evaluation of relationships between grain yield and agro-physiological traits of bread wheat genotypes under rainfed conditions

Drought stress, which is the most severe environmental problem limiting crop production in rainfed farming, can harshly affect plant growth and development, limit plant production and the crop performance. Drought stress is a polygenic stress and is considered as one of the most main factors limiting crop. The capability of a cultivar to produce high and satisfactory yield over a wide range of stress and non-stress environments is very essential. The response of crops to water stress depends on several factors such as developmental stage, severity and duration of drought and genotypes. Morphological characters such as spike.m-2, grain.spike-1, fertile tillers.plant-1, 1000-grain weight, peduncle length, spike weight, stem weight, awn length, grain weight per spike and affect wheat tolerance to the moisture shortage in the soil. The combination of high grain yield stability and high relative grain yield under dryland, has been proposed as it is a valuable selection criterion for characterising genotypic performance under a varying degree of drought. The objectives of this study were to screen wheat genotypes with high yield potential, stability, yield components under dryland conditions and to find out appropriate selection criteria for selecting genotypes tolerant to terminal heat stress.

In order to Study relationship between agro physiologic traits with grain yield under dryland conditions, as experiment was conducted at Payame Noor university of Ilam research station. Trials were designed using a randomized complete block with three replications in cropping season during 2016-2017. Plots were planted in eight rows measuring 4 m × 2 m. There was 25 cm distance between rows and 225 seeds m−2 were planted. Plots were fertilized with 120 kg ha−1 nitrogen and 50 kg ha−1 phosphorus at planting, and 60 kg ha−1 nitrogen (ammonium nitrate) was applied at stem elongation. Weeds were controlled by manual before stem elongation. Plots were harvested using the manual, with a 0.5 m edge left at both ends of the plot. Data were recorded for grain yield, plant height, biomass, harvest index, spikes m−1, grains spike−1, 1000-grain weight, peduncle length, RWC, Proline content and harvest index. Yield components were determined based on data from ten spikes. The data were analyzed statistically by SPSS program. Regression analysis was conducted to determine genetic progress over time, using years as the independent variable and productivity character as dependent variables. Average yield, regression coefficient, and total of squares of deviation from the regression were used to find out the stability for genotypes.

Results of descriptive analysis showed the most genotypic and phenotypic variation coefficient belonged to grain yield. Correlation coefficients showed that the highest correlation coefficient was between grain yield and biomass trait (r = 0.85**). The results of stepwise regression analysis, in which grain yield as dependent variable against the other traits was considered as independent variables, justify the three traits of biomass, HI and 1000- grain weight by 98 percent of the changes of the relevant regression model. Regarding stepwise regression analysis for grain yield in dryland conditions, by removing the biomass and HI from independent variables. three traits proline content, number of spikes per square meter and days of maturity entered the model, account for about 62 percent of grain yield changes in dryland conditions. The results of causal analysis showed that the direct effects of biomass, number of spikes per square meter and HI were positive most. The results indicate that there is a high genetic diversity among bread wheat genotypes under rainfed conditions. Biomass, HI, proline content, number of spikes per square meter and earliness can be identified as selection criteria for improving grain yield in dryland conditions

the studied genotypes showed a significant difference for all studied traits, indicating that there was a sufficient diversity among them. Based on the results of stepwise regression analysis, biomass, HI, spikes per square meter, proline content had a high contribution to grain yield and the most direct effects were related to biomass and HI. Therefore, biomass and HI as agronomic indices, proline content as a physiological trait of drought tolerance in dryland conditions can be used by breeders to select tolerant genotypes in bread wheat. It is also suggested that special attention should be paid to the reduction of the number of maturity days in wheat genotypes in order to increase yield in dryland conditions (drought stress).