Abstract: In order to study the mechanism of high temperature and humidity affecting the differentiation of tomato flower buds, the tomato variety ＂Shouhe Fenguan＂ was used as the test material. The orthogonal test of air temperature, air relative humidity and treatment days was conducted in the agricultural meteorological experimental station of Nanjing University of information technology from April to July 2020. The air temperature (day temperature / night temperature) was set with four treatment levels: T1 (32℃/22℃), T2 (35℃/25℃), T3 (38℃/28℃), T4 (41℃/31℃); The air humidity was set at three levels: H1 (50%), H2(70%) and H3（90%）, error range is ±5 percentage points. The treatment time was 2,4,6 and 8 days. The treatments of day / night temperature 28℃/18℃ and air relative humidity 45% − 55% were used as control (CK). The contents of endogenous hormones, starch and soluble sugar were measured at different stages of tomato flower bud differentiation, and stem diameter, dry weight of single plant, strong seedling index and chlorophyll content were measured at budding stage to study the mechanism of high temperature and high humidity on flower bud differentiation of tomato. The results showed that: (1) with the increase of temperature, the whole process of flower bud differentiation was prolonged with the increase of temperature, while the air relative humidity and treatment days had little effect on the process of tomato flower bud differentiation. (2) Under different treatments, the contents of IAA and GA3 in the top buds of tomato decreased, increased and decreased with the flower bud differentiation, while the contents of ZT and ABA showed the opposite trend with IAA. The contents of IAA, ZT and GA3 decreased with the increase of temperature, relative humidity and treatment days, while ABA content increased with the increase of stress degree. (3) The content of starch and chlorophyll in tomato leaves decreased gradually with the process of flower bud differentiation. Soluble sugar content increased gradually from non differentiation stage to stamen differentiation stage, and decreased gradually during pistil differentiation stage. With the deepening of stress degree, there were significant differences among the treatments. The results showed that the inhibitory effect of high temperature and high humidity on tomato flower bud differentiation might be related to the change of endogenous hormone content and the decrease of nutrients. The environmental temperature should be controlled at the level of CK at the initial stage of flower bud differentiation. The higher the temperature, the more unfavorable it would be. The results can provide some scientific basis for tomato growth environment regulation and disaster warning.

Key words: Tomato, High temperature, High humidity, Endogenous hormones, Flower bud differentiation process, Nutrients