Identification and screening of cold tolerance of direct-seedling early rice cultivars at seedling stage

Direct-seedling early rice is vulnerable to hypothermia，causing the seedling to rot or die.To reduces low temperature stress and select cold tolerance rice varieties at seedling stage to be direct seeding in early season， pot experiment with 18 early rice varieties was conducted under differently artificial low temperature（ 5.0℃） treatment and normal temperature condition. The results showed that 18 early rice varieties low temperature treatment indexs lower than normal temperature condition. The variation coefficient of seedling livabilit，aboveground biomass， the neumber of roots，root number，root volume，leaf area were relatively large under low temperature treatment， root volume ＞ seedling livabilit ≥ thir dleafunder the centralleaf area ＞ root number ＞ leafunder the centralleaf area ≥ second leafunder The centrallea area ＞ aboveground biomass. Accoording to factor analysis method showed that livabilit and aboveground biomass played a major role. Six stronger cold tolerance varieties，six intermediate cold tolerance varieties and six weaker cold tolerance varieties were obtained by using the method of subordination function method and accumulation analysis.