A field experiment was carried out at research station of Agricultural College, Karaj, in 2000. The study aimed to evaluate the effects of water stress on growth indices as well as their relations with yield and drought susceptibility/tolerance indices in eight cultivars representatives of four different climates in Iran. The experimental design was a split plot one with three replicates. Two irrigation levels applied represented the main plots and eight cultivars were allocated to subplots. Drought stress reduced both biological and grain yield in all cultivars. The highest reduction was observed in Roshan and Tajan, while the lowest in Chamran and M-75-7. Cultivars with higher yield under fully irrigated conditions were also superior under stress condition; the highest grain yield under stress condition being recorded for Shahpasand and Mahdavi and the lowest for Tajan. The highest values of stress tolerance index (STI) and mean productivity (MP) were observed in Roshan, Mahdavi and Shahpasand, whereas, Tajan displayed the lowest values. Water stress treatment did not affect specific leaf area (SLA) but, reduced leaf weight ratio (LWR) as well as leaf area ratio (LAR). Net assimilation rate (NAR) and relative growth rate (RGR), measured before flowering, were reduced by water stress. Significant negative relations were observed between NAR and STI,MP and yield. Of the two components of RGR, only LAR was positively correlated with RGR. Cultivars with higher LAR, showed lower NAR.
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