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.

Improving grain performance under water-limited conditions essentially depends on the knowledge of water-yield relationships. Th e current project was set up to make a fi eld evaluation of relations among grain yield, water use effi ciency (WUE), and its components, i.e., transpiration effi ciency (TE), uptake effi ciency (UE), and harvest index (HI) in bread wheat (Triticum aestivum L.) genotypes. Eight bread wheat genotypes and four water levels (WLs) based on evapotranspiration (ET; WL1, supplying 100% of ET water, to WL4, supplying 25% of ET water) were included in 3-yr experiments. Th e experiments were conducted under a line-source sprinkler irrigation system. Th e results of regression analysis revealed that grain yield, WUE, HI, TE, and UE showed linear regression lines against ET. Th ese regression lines ascended for grain yield, WUE, HI, and UE but descended for TE. Th e best-fi t model between WUE and its components was linear and showed an ascending trend for HI and UE but descending trend for TE. Th e results of this experiment showed that an increase in TE could improve the WUE in wheat genotypes considering that HI is high. Th at is, applying selection for both TE and HI under water-stress conditions might give the best results to improve WUE in breeding programs.

<p class="042abstractstekst">Sorghum (<em>Sorghum bicolor</em> (L.) Moench) is the fifth important cereal considered a drought-tolerant crop. However, its reduction of grain yield considerably occurs in a shortage of water. In the current study, 10 sorghum genotypes were assessed for their grain yield under normal irrigation and water deficit irrigation. As well, the efficacy of several drought indices was evaluated for the selection of high-yield and drought-tolerant genotypes. The experiment was conducted as a split-plot considering three irrigation levels as main-plot and 10 genotypes as sub-plot. Correlation among the indices, clustering of the genotypes along with principal component analysis was employed. Yield production was significantly and positively correlated with indices MP (mean productivity), STI (stress tolerance index), GMP (geometric productivity), HM (harmonic mean), and YI (yield index) in all the irrigation levels. Therefore, these indices are more effective in the selection of high-yielding genotypes under different water conditions. Rank means of stress indices for each genotype revealed that genotype TN-04-79 in mild deficit irrigation and genotypes KGS23 and TN-04-79 in severe deficit irrigation were the most tolerant.</p>