Identification of the most important traits affecting the yield of Aegilops tauschii ecotypes under drought stress conditions

Introduction:  Wheat is the most important crop that occupies the most area under rainfed cultivation. Drought stress is the most important factor in wheat yield reduction. The scope of this stress is expanding day by day in the world. Drought resistance is a quantitative trait with a complex phenotype that is affected by plant growth stages. Breeding requirements for resistance to drought stress in wheat are two factors: high genetic diversity among cultivated and wild genotypes of wheat and selection based on traits related to this resistance. One of the important strategies to deal with moisture stress is using wild relatives of wheat, especially the genus Aegilops, as one of the important gene sources containing genes for resistance to environmental stresses. Based on this limitation, the use of wild wheat relatives is one of the important goals of wheat breeding programs. This research aimed to evaluate the relationship between grain yield and 32 different phenological and agro-physiological traits in ten ecotypes of Aegilops tauschii which was carried out under moisture-stress conditions and for two period.   Materials and methods: This study was conducted for two consecutive periods in the research greenhouse of the Faculty of Agriculture of Bu-Ali Sina University in Hamedan. In this study, 33 phenological, morphophysiological, and root traits were evaluated in ten ecotypes of diploid wheat Aegilops tauschii (2n=2x=14, DD) under drought stress conditions. These ten different ecotypes of Aegilops tauschii were collected from different geographical regions of Iran.The mentioned ecotypes were evaluated in a randomized complete block design with three replications. At first, the seeds of the plant samples were grown in seedling trays containing equal proportions of perlite and cocopeat. Then, for the vernalization of the plants, after the initial germination of the seeds, in the two-leaf stage of the seedlings, the culture trays were moved to a cold room with a temperature of 4 degrees Celsius for about 35 days. After this stage, the vernalized seedlings were transferred to 10 kg pots, containing a combination of agricultural soil, sand, and rotted animal manure at a ratio of 50, 25, and 25%. After transplanting, the pots were irrigated at 100 percent of the soil's field or pot capacity for about two weeks. Then, in order to apply drought stress treatment, the humidity of the pots was kept at 45% of the field or pot capacity until the plants were harvested, by weighted moisture method.   Results and discussion: Economic yield has a positive and significant correlation (p≤0.01) with the traits of grain water use efficiency, peduncle length, plant harvest index, main spike weight, grain weight in main spike, number of fertile spikes per plant, thousand-grain weight, plant height, excited leaf water retention, number of grains per plant, peduncle weight and leaf surface index. This was despite the fact that most of the phenological and root traits had a significant negative correlation with grain yield. According to the stepwise regression results, the traits of grain water use efficiency and the number of fertile spikes per plant with a positive coefficient and the traits of root diameter and days to heading, with a negative coefficient, as the most important traits affecting grain yield, were entered into the regression model respectively. The results of the path analysis indicated that the trait of grain water use efficiency had the most direct and positive effect on increasing grain yield. Also, the trait of water use efficiency, through the trait of day to heading, had the most negative indirect effect on grain yield.   Conclusion: According to our findings, the selection based on higher values of grain water use efficiency and the number of fertile spikes per plant and lower values of phenological and root traits may lead to improvement of wheat grain yield under drought stress conditions.