Ph.D. Dissertation:

Response of yield,yield components and biochemical characteristics of cotton to concentration and type of stress modifier in common and delayed planting in saline conditions

Increased activities of enzymatic and non-enzymatic antioxidants provide a common reaction to environmental stress in most crops. To investigate the effect of foliar application of stress moderators on enzymatic and non-enzymatic antioxidant changes, field experiments were conducted as split-plot design based on a randomized complete block design with three replications in 2017 and 2018. Planting date (early and late) was considered as the main plot, and foliar applications with 50 and 100 mM of Glycine Betaine, 1 and 2 mM of salicylic acid, and 100 and 200 µM of sodium nitroprusside, along with the control treatment, were regarded as the subplot. The results showed that the amounts of chlorophyll pigments and the levels of enzymatic antioxidants (glutathione peroxidase, ascorbate peroxidase, superoxide dismutase, catalase), and proline increased, and H2O2 level decreased with the foliar application of stress moderators. Glycine betaine and sodium nitroprusside had the lowest and highest effects on the enzymatic antioxidant activities, respectively. The analysis of the main components revealed that in the early and delay planting date, the characteristics of enzymatic antioxidants and photosynthetic properties had the greatest effects on the enhancement of tolerance to salinity stress. In general, the results of this research demonstrated that the elevated activities of enzymatic antioxidants compared to non-enzymatic ones were more effective in reducing the impacts of salinity stress. Moreover, the foliar application of sodium nitroprusside at a concentration of 100 µM served as the most suitable moderator for augmenting the activities of enzymatic antioxidants in salinity stress conditions.

Keywords: Antioxidant enzymes  Glycine betaine  Salicylic acid  Salinity stress  Sodium niroporoside