ABSTRACT: BACKGROUND:Rice is the staple food of many people around the world. However, most rice varieties, especially widely grown indica varieties and hybrids, are sensitive to cold stress. In order to provide a basis for the utilization of a common wild rice (CWR, Oryza rufipogon Griff.) named 'Chaling' CWR in cold-tolerant rice breeding and deepen the understanding of rice cold tolerance, the cold tolerance of ratoon 'Chaling' CWR was studied under the stress of the natural low temperature in winter in Changsha, Hunan province, China, especially under the stress of abnormal natural low temperature in Changsha in 2008, taking other ratoon CWR accessions and ratoon cultivated rice phenotypes as control. RESULTS:The results showed that ratoon 'Chaling' CWR can safely overwinter under the natural conditions in Changsha (28° 22' N), Hunan province, China, which is a further and colder northern place than its habitat, even if it suffers a long-term low temperature stress with ice and snow. In 2008, an extremely cold winter appeared in Changsha, i.e., the average daily mean temperature of 22 consecutive days from January 13 to February 3 was -?1.0 °C, and the extreme low temperature was -?4.7 °C. After subjected to this long-term cold stress, the overwinter survival rate of ratoon 'Chaling' CWR was 100%, equals to that of ratoon 'Dongxiang' CWR which is northernmost distribution in the word among wild rice populations, higher than those of ratoon 'Fusui' CWR, ratoon 'Jiangyong' CWR, and ratoon 'Liujiang' CWR (63.55-83.5%) as well as those of ratoon 'Hainan' CWR, ratoon 'Hepu' CWR, and all the ratoon cultivated rice phenotypes including 3 japonica ones, 3 javanica ones, and 5 indica ones (0.0%). CONCLUSIONS:The results indicate that ratoon 'Chaling' CWR possesses strong cold tolerance and certain freezing tolerance.
