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Title:   Author  item
                                            Kim, Sang Icitem
                                            Tai, Thomas
  Submitted to: Euphytica
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 12/1/2010
                                    Publication  Date: 4/1/2011
                                    Citation: Kim, S., Tai, T. 2011. Evaluation of seedling cold tolerance in rice cultivars: a comparison of visual ratings and quantitative indicators of physiological changes. Euphytica. 178:437-447.Interpretive Summary: Rice seedlings are sensitive to low temperature and after two weeks severe tissue injury is evident in some varieties. This can result in seedling death or at least poor development that will affect yields. Assessment of cold or chilling tolerance is usually performed using a visual rating system. Here we report the evaluation of M-202 (cold tolerant) and IR50 (sensitive) by quantifying compounds associated with physiological and biochemical changes that occur during cold stress. Our results are compared to the traditional visual assessment which has been previously used to assess cold tolerance in genetic studies of M-202 and IR50. Taking both the quantitative and qualitative data, we have identified rice varieties that are more tolerant than M-202. IR50 was shown to be among the most sensitive varieties. These varieties identified here can be used for genetic studies on the seedling cold response and the tolerant lines will be used to develop rice germplasm with improved cold tolerance for temperate breeding programs.
                                Technical Abstract: 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.


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