Evaluation of seedling cold tolerance in rice cultivars: a comparison of visual ratings and quantitative indicators of physiological changes

Rice (Oryza sativa L.) is sensitive to prolonged exposure to low temperature, which at the seedling stage can result in significant chilling injury and mortality. The objective of this study was to quantify physiological and biochemical changes in rice seedlings undergoing chilling stress and compare those changes with visual evaluation of tolerance. Seedlings from the cultivars M-202 (tolerant) and IR50 (sensitive) were subjected to 9°C for 14 days in a controlled environment chamber. Leaf tissues were harvested at various time points for determination of electrolyte leakage, proline, malondialdehyde, ascorbic acid and reduced glutathione. Significant differences between M-202 and IR50 were detected in electrolyte leakage, proline, and ascorbic acid starting at 7 days with IR50 exhibiting higher levels of these indicators. Most IR50 seedlings were dead at 14 days. A set of fifty rice accessions including M-202 and IR50 was evaluated at 10 days of cold treatment to examine the correlation of visual ratings with the physiological indices. Visual ratings were most highly correlated with electrolyte leakage and least correlated with proline content. Based on visual ratings and the physiological indices, we identified several cultivars that outperformed M-202 in cold tolerance while IR50 had the lowest tolerance of the cultivars tested.