Morphological and Physiological Responses of Cotton to Combined Effect of Elevated Ultraviolet-B Radiation and Boron Deficiency.

Plants are exposed to a combination of different soil and atmospheric abiotic stresses that hamper growth and productivity through modulation of physiological processes. The present study was conducted to investigate the combined effect of elevated ultraviolet-B (UV-B) radiation (0, 5 and 10 MJ m^-2 day^-1) and boron deficiency on growth and physiology of two cotton cultivars (Arkot 9704 and UA48). High UV-B radiation treatment was imposed after the completion of emergence and boron deficiency was induced two weeks after UV-B treatment in sand culture. Boron deficient plants received boron-free nutrient solution while others received normal boron-containing nutrient solution. The elevated UV-B radiation and boron deficiency alone or in combination decreased the plant height, number of nodes, photosynthetic rate, transpiration rate, stomatal conductance, carboxylation use efficiency, efficiency of photosystem II (Fv/Fm), quantum yield of photosystem II and electron transport rate (ETR) of cotton. However, the combined effect of high UV-B radiation and boron deficiency was more deleterious on cotton growth and photosynthetic efficiency. Between cultivars, the UA48 (Ark 0102-48) performed better for all studied attributes, as compared to Arkot 9704. The higher tolerance of UA48 was associated with better leaf gas exchange and efficiency of PSII under elevated UV-B radiation and boron deficiency stress. This research was partially supported by a Pakistan Higher Education Commission Fellowship to AZ.