Characterizing Physiological Responses to Plant Water Status during Progressive Drought As a Means to Identify Drought Tolerance in Commercially-Available Cotton Cultivars

A number of rapid, non-destructive techniques using chlorophyll fluorescence have been proposed to screen for drought stress tolerance. The appeal of chlorophyll fluorescence is that it is rapid (approximately 1 second per measurement) and a large number of parameters can be determined per reading (quantum yield, electron transport rate, performance index, etc.). However, information is limited on the efficacy of using chlorophyll fluorescence to predict photosynthetic and yield performance under dryland conditions. This information will be exceptionally useful in identifying a meaningful and rapid screening tool for drought tolerance in cotton. To this end, three cotton cultivars were grown under well watered conditions until first flower, at which time irrigation ceased and a rainout shelter was utilized to prevent rainfall interception by the crop. During a three week drying period, predawn water potential, maximum quantum yield of photosystem II, dark respiration, net and gross photosynthesis, photorespiration, photosynthetic electron transport rate, non-photochemical quenching, OJIP analysis (a relatively recent chlorophyll fluorescence-based methodology), and end of season lint yield were utilized to characterize cultivar responses to soil drying with the goal of identifying cultivar differences in drought tolerance.