Ph.D. Dissertation:

Agrophysiological response of cotton to time and type of osmotic modifier incommon and delayed Planting date in saline conditions

Environmental stress has been always a main cause of reduced yields in agricultural crops. Today, determination of appropriate planting times and application of stress moderators have been considered for mitigating the negative effects of stress on crops. In this study, the impacts of varied times and types of consumed moderators on the yield, yield components, and biochemical traits of cotton were investigated based on the two traditional sowing date and delayed cultivation under salinity conditions during 2017 and 2018. The research was based on a factorial split-plot experiment in a randomized complete-block design with 3 replications. Sowing date (traditional planting date and delayed cultivation) as the main plot and stress moderator type at 4 levels (control, 2mM Salicylic Acid (SA), 100 mM Glycine Betaine (GB), and 100 ?M sodium nitroprusside (SNP)) and application time (flowering and flowering + bolling stages) as the sub-plots were considered in a factorial design. The delays in planting cotton reduced height, number of vegetative branches, number of bolls, yield (biological yield, lint yield, seed cotton yield, and seed yield), 1000-seed weight in the 1st year, seed cotton length and index, number of seeds, and chlorophyll a content. Foliage time affected most morphological and physiological traits except the number of vegetative branches, biological yield, lint, 1000-seed weight, seed cotton index, hydrogen peroxide, carotenoids, membrane stability index, catalase, ascorbate peroxidase, and sodium. Spraying with the stress moderators in the salinity conditions alleviated the negative effects of soil salinity on the physiological and morphological traits of cotton. The highest boll weight, yield (biological and seed cotton yields), and catalase amount were observed with SA consumption; the highest number of open bolls and hydrogen peroxide content were seen with SNP application; and the highest contents of carotenoids and total chlorophyll were witnessed with GB spraying. Enhancements of most traits, except for the number of vegetative branches, superoxide dismutase, and hydrogen peroxide, which showed the highest number and amounts in the delayed planting date, were related to foliar application at the flowering + bolling stage in the traditional sowing date. However, most traits were not influenced by the delayed cultivation and foliar spraying at the flowering stage. In the delayed sowing conditions, most traits did not respond to spraying with the consumed moderators, except for the number of vegetative branches in the 2nd year and the amounts of hydrogen peroxide, carotenoids, superoxide dismutase, catalase, and sodium. While spraying with SNP in the traditional sowing date yielded the greatest elevations in the studied traits, there was no significant difference between spraying with SNP and SA in most of the traits. Accordingly, cotton planting at the appropriate date and spraying with SNP could be recommended to produce the most suitable yield in salinity conditions. Also, the best time for foliar application of SNP was at the lowering + bolling stage though the use of SNP did not show any difference with SA consumption in most traits. Furthermore, foliar application of SNP at the flowering + bolling stage in the traditional sowing date caused the greatest increase in the traits.

Keywords: yield components, cotton, sowing date, foliage time, osmotic protector