Differential response of two important Southern US rice (Oryza sativa L.) cultivars to high night temperature
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The impact of climatic change on crop production is a major global concern. The climatic factor, night temperature, increasing as a result of global warming, can alter rice productivity and quality. As the initial step in development of high night temperature (HNT; 30 C)-tolerant rice cultivars for the Southern United States (US) and similar climates, in this study we screened two popular Southern US rice cultivars 'Cocodrie' (inbred pure line) and 'XL723' (hybrid) for variation in tolerance to HNT. Plants were exposed to ambient night temperature (ANT; 25 0.5 C) and HNT (30 0.5 C) from 30 days after emergence (DAE) until harvest in the greenhouse. Growth, morphological and physiological traits of Cocodrie and XL723 were examined. The HNT did not affect plant morphology, leaf photosynthetic rate or leaf pigments for rice cultivars 'Cocodrie' and 'XL723'. For 'Cocodrie', HNT increased leaf internal CO2 concentration (ICO2; 3%), respiration rate (RS; 21%) and relative injury to the leaf membrane (RI; 35%) and decreased pollen germination (49%), spikelet fertility (40%), and yield (10%). For 'XL723', HNT increased ICO2 (3%), RS (36%) and RI (28%) and decreased pollen germination (36%), spikelet fertility (13%), and yield (6%). In this study, 'XL723' yielded (4%) more than 'Cocodrie' under HNT as a result of lower RI (7%) and higher pollen germination (13%) compared to 'Cocodrie'. The RI and pollen germination, individually or in combination, can be used as screening tools for HNT tolerance in future breeding efforts to enhance HNT tolerance in Southern US rice cultivars.