Genetic variation of chilling injury at seedling stage in rice, Oryza sativa L.

Abstract

To identify an effective method of evaluation of the chilling injury at the seedling stage of rice, 15 combinations of temperature and duration of treatment were examined. Exposure of 12-day-old seedlings to a temperature of five degrees centigrade for 4 days resulted in the widest range of degrees of injury, which produced the optimum conditions for evaluating this character. The reactions to the low temperature indicated wide genetic variations in a total of 2, 151 indigenous varieties which originated from various countries. Most of the varieties from high latitudes, Japan, Europe, USA and USSR, were tolerant (Grades 0 to 2), while the varieties from low latitudes, India and Nepal, were predominantly sensitive (Grades 4 to 6). Most of the varieties from Indonesia and the Philippines were relatively tolerant although those countries are located at lower latitudes. Some varieties from Laos, Thailand, Myanmar and Southwest China cultivated in hilly areas were also tolerant. Distinct geographic clines in the variation then occurred along a latitudinal axis. The areas located in Southwest China, Myanmar, Laos, Thailand, Bhutan and Malaysia exhibited a rich diversity in the variations of this character.