Abstract: The effects of day and night temperature difference (DIF) on tomato’s growth were studied in three precisely controlled units in phytotron. Set DIF as 6 ℃ (25/19 ℃), 8 ℃ (26/18 ℃), 10 ℃ (27/17 ℃) respectively, with the same diurnal mean temperature as 22 ℃. The results showed that, different tomato varieties needed different suitable DIF at different growth stages. Before flouring, compared with DIF 6 ℃, DIF 8 ℃ could significantly improve the growth and development of the wild currant tomato LA1781, increasing the plant height by 23.1%, fastening leaf development by 1-2 leaves, advancing flowers by 7 d. DIF 10 ℃ had similar effects with DIF 8 ℃ on LA1781. As to the cultured ordinary tomatoes LA2397 and LA0490, DIF 6 ℃ made the seedlings grow well, DIF 8 ℃ had no significant improved effects on seedlings, DIF 10 ℃ depressed the seedling’s growth and flouring, decreasing the plant height by 12.0%-18.3%, lowering the leaf development by 2-3 leaves, delaying flouring by 2-4 d. But DIF 10 ℃ increased the dry aboveground mass  of these three varieties by 25.2%-44.2%. After flouring, compared with DIF 6 ℃, DIF 10 ℃ could significantly improve the yield and fruit quality of LA1781, increasing fruit number by 34.7%, yield per plant by 92.1%, single fruit mass by 40.0%, soluble sugar content by 16.3%, lycopene content by 95.6%.
Compared with DIF 6 ℃, LA2397 and LA0490 had higher yields and better fruit quality under DIF 8 ℃, and lycopene content increased more than twice as that under DIF 6 ℃. Under DIF 10 ℃, yields of LA2397 and LA0490 slightly decreased (5.0%), soluble sugar contents of fruit decreased, but fruit size and lycopene content increased. The results showed that, DIF should not be very great in the seedling period of tomatoes, and a moderate DIF in flower and fruit periods could improve the yield and fruit quality, but a too high DIF would result in poor growth and yield reduction.