Boeoticum specie is a valuable drought-tolerance gene source to breed wheat yield under stress. This study was done to identify the most important traits affecting grain yield of 10 boeoticum ecotypes under drought stress conditions for two years. Water use efficiency, fertile spikes number per plant and seed number per plant showed the highest positive and significant (p≤0.01) correlation with grain yield per plant. Water use efficiency, fertile spikes number per plant, seed number per the main spike, biological yield per plant, and water use (with a negative regression coefficient), as the most important traits, were entered into the regression model, respectively. The most direct effect on increasing grain yield was water use efficiency. Seed number per plant and fertile spikes number per plant, due to increased water use efficiency, showed the most indirect effect on grain yield. Ecotype 5, as a drought-tolerant ecotype, showed a high water use efficiency by allocating more assimilates to yield components. It had a high grain yield. On the other hand, ecotype 6 was introduced as the most drought-susceptible ecotype with low-economical yield. In this study, high water use efficiency increased the traits related to seed number per plant. The ratio of assimilating allocation to aboveground or under-ground parts was the main mechanism for the adaptation of ecotypes. Therefore, selection based on these mechanisms will lead to the identification of drought-tolerant ecotypes for future wheat breeding programs.
