Evaluation of drought tolerance of wheat cultivars under water deficiency stress after flowering

 and objectives; In semi-arid regions, including large areas of Iran, decreasing soil moisture due to lack of rainfall and abrupt increase in temperature during the grain filling period, which is one of the most important factors in reducing growth of wheat, is a predominant climatic phenomenon. By recognizing the effects of drought stress and determining biochemical and molecular reactions to drought, the best response of the plant can be identified and used in breeding programs for select and produce new cultivars. The aim of this study was to investigate the effect of drought stress after flowering on some of the biochemical and antioxidant compounds of bread wheat cultivars and to identify some of characteristics of tolerant cultivars; those could increase both the tolerance and the production of yield in such conditions.

 Experiment was carried out in a field in north Aq-Qala, in a split plot model based on a complete randomized block design with three replications in 2016-2017. Moisture treatments in the main plots were consisted of optimal irrigation during the growing season (A1), irrigation interruption from the start of seed filling (A2), and irrigation interruption from the flowering stage (A3). And cultivars treatments in the sub plots were four wheat cultivars. In this experiment, the amount of optical pigments (chlorophyll a, b, and carotenoids) were investigated as sources of photosynthetic materials production, changes in the amount of water soluble carbohydrates (WSC) during the stress period as a compensatory source of grain, as well as the content of malondialdehyde (MAD) as the amount of damaging the cell membrane and the activity of superoxide dismutase (SOD) and peroxidase (POD) enzymes as plant enzymatic resistance against oxidative stress. Results and

The results of this experiment show the grain yield was reduced, with increasing tension, from 535 g/m2 in A1 to 464 g/m2 in A2, and 437.6 g/m2 in A3. With increasing tension the amount of remobilization of WSC to seed from A1 to A2 and A3 was increased from 16.8 to 29.9 and 37.5 mg/g respectively. The cultivars of Kuhdasht and Karim (35.9 and 33.3 mg/g, respectively) indicated that they had better WSC remobilization than Ehsan and Gonbad (17.1 and 25.8 mg/g respectively). The activity of peroxidase and superoxide dismutase enzymes did not show any significant differences among Tolerant and sensitive cultivars under full irrigation

but the activity of these enzymes in treatments of irrigation cutting in Kuhdasht and Karim cultivars was more than Ehsan and Gonbad. The content of malondialdehyde increased further with increasing water stress in Ehsan and Gonbad cultivars compared with Kuhdasht and Karim cultivars Conclusions; The results showed that under drought stress conditions, the more increase of activity of antioxidant enzymes, POD and SOD, in Kuhdasht and Karim cultivars, compared with Ehsan and Gonbad ones, prevented more damages of oxidative stress on cell membrane so causes lower MAD content. The cultivars of Kuhdasht and Karim showed that under post-flowering stress conditions, could maintain a higher chlorophyll a, b and higher carotenoids as sources of photosynthetic material production. This feature enabled them to sustain higher yields under drought conditions by continuance of further production of photosynthetic materials and securing more seeds. The results also indicated that Kuhdasht and Karim cultivars had higher remobilize of SWC than those of Ehsan and Gonbad.