Evaluation of Cold Tolerance Traits for Improved Japonica Rice under Low Temperature Stress

The cold tolerance at the booting stage and main agronomic traits of 347 improved japonica rice varieties,which were from nine countries and eleven provinces of China,were evaluated under natural low temperature and cold water irrigation and the cluster analysis of the varieties was conducted.The results showed that the main agronomic traits associated with cold tolerance and cold water response index(CRI)among the varieties were significant different under natural low temperature and cold water irrigation.Under both conditions seed setting rate at the booting stage and CRI of the improved rice varieties from Yunnan Province and Japan were higher than those of other countries or provinces.From the overall trend,The cold tolerance at booting stage of the varieties from relatively higher latitude of north provinces were stronger than those from relatively low latitude of southern provinces except few provinces under natural low temperature.However,under cold water irrigation,the relationship between the cold tolerance and origin of varieties was not close and did not show a regularity.In addition,the cluster analysis of the improved japonica rice varieties were associated with geographical locations.Moreover,the results was associared more closely with origins of varieties under cold water irrigation than natural condition.