Comparison of Pima and upland cotton species in terms of their morphological, physiological and biochemical characteristics related to heat resistance under high temperature environments

Because of the great influence of environmental stress on agriculture productivity, desirable ecophysiological and biochemical traits for selection need to be studied with the aim of improving stress resistance and economic productivity. The main objective of this research was to provide further understanding on interactions between plant properties and environmental factors, and on the functional relationship between plant ecophysiological and biochemical characteristics and heat resistance, through comparison of two contrasting cotton species, Pima cotton (Gossypium barbadense) and upland cotton (Gossypium hirsutum), in high temperature environments. All field studies were carried out at the USDA Agricultural Research Station at Maricopa, Arizona, and laboratory experiments were conducted in a greenhouse and labs at the University of California, Los Angeles. In the first chapter, leaf properties relating to heat resistance were studied using a leaf energy budget approach. The second chapter describes the biochemical differences in terms of photoprotective mechanism and photosynthetic properties between the two cotton species. In the last chapter, I considered the genetic variations of heat resistance-related ecophysiological properties to explore the potentiality of selection for those desirable traits in increasing heat resistance and yield potential.;The results obtained indicated that high stomatal conductance and smaller leaf size found in leaves in upland cotton species had profound effect on lowering leaf temperature. In upland cotton leaves high zeaxanthin content may provide a strong ability to photoprotection, which, combined with the ability of lowering leaf temperature, could be the reason of maintaining high photosynthetic rates in the hottest time during the day. Furthermore, the high photosynthetic rates and the consequential high sucrose and starch content found in source leaves would certainly contribute to the high lint yield in upland cotton. The heat resistance-related ecophysiological properties, such as stomatal conductance, leaf size and photosynthetic rates, were under the genetic control.;Taken together, these findings provide evidence that plant ecophysiological and biochemical properties play an important role on stress resistance, and selection for the identified traits related to stress resistance would greatly improve crop productivity in unfavorable conditions.