Abstract: 【Objective】 The effects of low temperature on the germination indexes of different watermelon materials were studied,and the low temperature tolerant germplasm materials were screened to provide theoretical reference for the breeding of low temperature tolerant watermelon varieties.【Methods】Thirty-nine watermelon varieties（lines）and combinations were used as experimental materials,and a few incubators were used to simulate different low temperature stresses（15/10 ℃,15 ℃ and 17 ℃）.The effects of low temperature stress on germination potential,germination rate,radicle length,vigor index,chilling injury index and recovery ability of watermelon seeds were analyzed,furthermore,and the low temperature tolerance of different watermelon materials was evaluated by pole-sorting method.【Results】Germination potential,relative germination rate,relative radicle length and relative vigor index were decreased under low temperature stress,and the inhibition was more obvious with the decrease of stress temperature.The germination potential,relative germination rate,relative radicle length and relative vigor index of watermelon seeds were significantly correlated with the comprehensive evaluation score of low temperature tolerance,and the relative vigor index and the evaluation scores exhibited the highest correlation（r=0.949）.Different watermelon materials had different tolerance to low temperature during germination.At 17 ℃,there were significant differences in germination potential,relative germination rate,relative radicle length and relative vigor index among different watermelon materials.The four indexes and chilling injury index were selected and the comprehensive evaluation score of each watermelon material was obtained by using the pole sorting method.The results showed that the comprehensive evaluation score of 170-1 was higher than 5,which was a low temperature resistant material.The comprehensive score of Qianli 4,Sumi 1667,Qianli 1,reciprocals of Qianli 4,Qianmei 1,135-2,161-5,17A-81×17A-82 were lower than 2,which were low temperature sensitive materials,anothers were medium low temperature resistant materials.【Conclusion】Low temperature inhibited the germination of watermelon seeds,17 ℃ could be used as the suitable temperature for identification of low temperature tolerance of different watermelon materials at germination stage,watermelon materials with different low temperature tolerance could provide experimental materials for breeding of low temperature tolerant varieties and basic theoretical research.

Key words: Watermelon, Low temperature, Germination, Chilling injury