S.H. JUMAA1, E.D. REDOÑA2, T. WALKER3, W. GAO and K.R. REDDY1*
Temperature is one of the key abiotic stress factors that affect various stages of plant growth and development. In the US Midsouth, rice plants get exposed to variable temperatures depending on the planting date. We hypothesize that rice cultivars vary in their response to temperature, and developing a method for low- and high-temperature tolerance screening will help producers and breeders to select cultivars for management and breeding, respectively. Four rice cultivars, CL152, Bowman, Antonio, and Mermentau along with two hybrids XL 753 and CLXL 745 that were the most commonly grown in the US Midsouth were evaluated in this study for temperature tolerance. Five day/night temperature treatments, 20/12 (very low), 25/17 (low), 30/22 (optimum), 35/27 (high), and 40/32 °C (very high) were imposed after the seedling establishment, ten days after planting (DAP). Growth and developmental parameters including root and physiological parameters were recorded from plants harvested at 39 DAP. Rice cultivars and hybrids exhibited significant variability in their response to low and high temperatures. Based on total low- and high-temperature response indices, relative temperature response scores were derived. Total low-temperature response index values ranged from 18.48 to 23.15 whereas total high-temperature responses index values ranged from 42.01 to 48.82. Antonio, CLXL 745, and Mermentau were identified as sensitive to cold and heat, Bowman as sensitive to cold and moderately sensitive to heat, CL152 was moderately sensitive to cold and heat, and XL 753 was highly cold and heat tolerant cultivars/hybrids tested. These results may be useful for breeders to develop new rice cultivars which could withstand low- and high-temperature conditions during seedling stages. Further large-scale studies are needed to evaluate more cultivars or lines both in the controlled environments and field settings to come up with practical recommendations.
Key words: Rice (Oryza sativa L.), temperature, morpho-physiological parameters, root growth and developmental traits, SPAR, Total Drought Response index (TDRI), TLTRI, Total low temperature response index; THTRI, total high temperature response index; SD, standard deviation; r2, coefficient determination; PH, plant height; TN, tillers number; LN, leaves number, LA, leaf area; LW, leaf weight; SW, stem weight; RW, root weight; AGW, above ground weight; TW, total weight; RS, root/shoot; RL, root length; RSA, root surface area; RAD, root average diameter; RV, root volume; RNT, number of tips; RNF, number of forks; RNC, number of crossing; SPAD, chlorophyll content; Fv’/Fm’, fluorescence
Key findings: Temperature affects all shoot, root and physiological parameters. Cultivar differences were observed for low and high-temperature responses during the early-season.