Abstract: Based on microclimate observed meteorological data within a greenhouse from December 2017 to February 2018 in Inner Mongolia, the tomato growth data and frost damage factors were analyzed, and the regression models of daily minimum temperature inside and outside greenhouse under different weather conditions were established. Meanwhile, the minimum temperature index of different levels for tomato freeze injury was ascertained. The results showed that, the occurrence of low temperature and freeze injury for greenhouse tomato was not only related to the daily minimum temperature, but also to the duration of low temperature and relative humidity. The quadratic curve of daily minimum temperature inside and outside the greenhouse was fitted the best in clear,cloudy and overcast days,and the correlation coefficients were 0.733, 0.820, and 0.423, respectively. The temperature forecast index for mild freeze injury was -18.5~-10.4 ℃, -10.6~-7.4℃, and -8.4~-4.4℃ in clear,cloudy and overcast days, the temperature forecast index for moderate freeze injury was -20.5~-18.5 ℃, -13.0~-10.6 ℃, and -11.4~-8.4 ℃ in clear,cloudy and overcast days, and the corresponding values for severe freeze injury were ≤-20.5 ℃, ≤-13.0 ℃, and ≤-11.4 ℃ in three weather conditions, respectively.

Key words: greenhouse, tomato, low temperature and freeze injury, regression model, Inner Mongolia