No abstract

Evaluating physiological traits involved in the response of plants to drought stress could lead us to improve drought tolerance in crops. In this regard, the current project was conducted under a line-source sprinkler irrigation system. Eight commercial bread wheat cultivars {Triticum aestivum L.) were evaluated at four water levels (WL) based on evapotraspiration (ET; WL1, supplying 100% of ET water to WL4, supplying 25% of ET water). Among the cultivars Chamran and Kavir had the highest grain yield at WL4 (4450.7 and 4317.3 kg ha-\ respectively) and noticeable grain yield stability in different water levels. Water use efficiency (WUE) ranged between 5.092 and 7.296 kg ha"m m"^and significantly varied among cultivars in different WLs. Under WL4, Niknejad and Kavir had the highest and Shiraz had the lowest value for WUE. Regression analysis confirmed that the relationship between dry matter and ET follows a linear function. Furthermore, evapotranspiration efficiency (ETE) as calculated by dividing the total biomass by ET was a reliable physiological indicator for cultivar evaluation with regard to water deficit tolerance in different growing stages. Based on this indicator, it was discovered that Mahdavie has the highest ETE from planting to stem elongation, Niknejad from planting to flowering, Pishtaz from planting to dough development and ripening, and Kavir has tolerance against water deficit throughout the growing season.