Response of Two Southern US Rice (Oryza sativa L.) Cultivars to High Night Temperature.

The impact of climatic change on crop production is a major global concern. One of the climatic factors, night temperature (NT), which is increasing as a part of global warming, can alter crop productivity and quality. A study was conducted to evaluate the effects of high night temperature (HNT) on morphological, phenological and physiological parameters of two popular but contrasting rice cultivars of the U.S. mid-south growing region. The cultivars used in this study were ‘Cocodrie’ (inbred line) and ‘XL723’ (hybrid). Plants grown in the greenhouse at the Texas AgriLife Research and Extension Center in Beaumont, Texas, U.S.A. were exposed to 25 ^oC and 30 ^oC NT from 30 days after emergence (DAE) until harvest. Differential response between the cultivars to HNT was seen with respect to several physiological parameters, dry weights and leaf photochemistry. However, HNT did not affect morphology, phenology, leaf photosynthetic rates or leaf pigments in either cultivar. The HNT increased leaf internal CO₂ concentration, respiration rates and relative membrane injury to the membrane increased by 3%, 36% and 21%, and 3%, 28% and 34% in ‘Cocodrie’ and ‘XL723’, respectively. The HNT decreased pollen germination and panicle dry weight by 65% and 10% and 67% and 6% in ‘Cocodrie’ and ‘XL723’, respectively. In this study, cultivar ‘XL723’ performed better than cultivar ‘Cocodrie’ under HNT.