Abstract: In order to study meteorological index of high temperature damage to early rice at the early milk stage, the control trials of daily maximum temperature (between 34℃ and 39℃) of hybrid rice Ganxin 203 at the early milk stage were carried out in the climatic cabinets. And the natural temperature was taken as the contrast. The ripening rate, blighted grain rate, 1000 grains weight and yield per plant of each material, which were closely related with high temperature damage to early rice at the early milk stage, were analyzed by using principal component analysis and hierarchical cluster analysis. The results showed that the meteorological index of high temperature damage to early rice at the early milk stage could be classified into three grades, including light, moderate and severe damage, that was, daily maximum temperature of 35℃ for 5 days, or 36℃ for 4 days, or 37℃ for 3-4 days, or not less than 38℃ for 3 days belonged to light damage，daily maximum temperature of 35℃ for 6-8 days, or between 36 and 37℃ for 5 days, or not less than 38℃ for 4-5 days belonged to moderate damage; daily maximum temperature of 35℃ for greater than 8 days, or not less than 36℃ for 6 days and above belonged to severe damage. Relative to original index, the new index, which considered not only the high temperature strength and duration, but also their coordination, was more sensitive to the identification of heat damage, and every damage grade had its daily maximum temperature and duration. The results could support scientific foundations for monitoring and warning, risk assessment and division of high temperature damage to early rice.

Key words: Early rice, High temperature damage, Meteorological index, Principal component analysis, Hierarchical cluster analysis