The major environmental factor limiting the range of adaptation for wheat is drought. Fourteen wheat genotypes (Triticum aestivum L.) were grown under two environments (irrigated and rain fed) to determine physiological and photosynthetic responses to drought. Combined analysis of variance of the data showed that the environment was a significant source of variation for leaf chlorophyll content (LCC), stomatal conductance (g(s)) and grain yield (GY). Wheat genotypes differed significantly for LCC, g(s) and GY. All the measured traits under water-stress conditions except maximum photochemical efficiency of PSII (F(v)/F(m)) were lower than those under nonstress conditions. Mean GY in rain-fed conditions was 11.26% lower than that in irrigated conditions. The genotypes number 13 (Marvdasht) and 8 (M-81-13) exhibited the highest GY per unit area in both irrigation and rain-fed conditions. It was concluded that the higher LCC and g(s) under drought-stress conditions could possibly be the proper criteria for screening the drought-tolerant wheat genotypes under field conditions.

Drought is a widespread problem seriously influencing wheat production and quality, but development of resistant cultivars is hampered by lack of effective selection criteria. Based on recent rates of increase, the world population is expected to double from 6 billion in the next 50 years. Proper management of input using modern technology, particularly irrigation water management, is essential to maximize crop production and return for the farmers. Fourteen wheat genotypes (Triticum aestivum L.) were grown under two environments (irrigated and rain-fed) to determine morphological and phenological responses to drought. The results of combined analysis of variance for spike length, awn length, peduncle length, plant height, days to heading, grains/spike and grain yield indicated that genotypic differences were significant (P<0.01). No significant effect was observed for spike length under each of stress and non-stress conditions. The highest peduncle length was observed for Marvdasht followed by M-83-6 and M-81-13 under rain-fed conditions. Grain yield was positively correlated with spike length, peduncle length and grain/spike, but negatively correlated with plant height in the both environments. Average grain yield in rain-fed conditions was 11.26% lower than that in irrigated conditions. Marvdasht cultivar (G13) had the highest grain yield in both conditions, while the lowest grain yield belonged to accessions 1 and 4 (Hamam-4). Marvdasht, M-81-13, WS-82-9, PYN and Shiraz were the most productive genotypes in irrigated conditions but in rain-fed site, Marvdasht followed by M-81-13, M-83-6, STAR, M-79-7 and TEVEES had the highest grain yield. Marvdasht was the superior wheat genotype under both rain-fed and irrigated conditions.

The effects of mild terminal drought stress on physiological parameters and activities of peroxidase (POX), catalase (CAT) and superoxide dismutase (SOD) were investigated in ten durum wheat genotypes using two field experiments under rain-fed (terminal drought stress) and irrigated (non-stress) conditions. Stress intensity was calculated to be 0.1 indicating mild water deficit stress. Based on combined analysis of variance, the mild terminal drought stress increased the activity of CAT while, POX and SOD content decreased significantly. Rain-fed durum wheat plants showed non-significant increases in photochemical efficiency of PS II (Fv/Fm) as compared to the irrigated plants. Chlorophyll concentration in the flag leaves of the plants under terminal drought decreased slightly than normal conditions. The interaction of cultivar and environment was significant for enzyme activities, indicating different biochemical reaction of durum wheat plants in the two conditions.