【Objective】To provide theoretical reference for the rapid screening of breeding materials for high-temperature tolerance and summer planting layout in Guangxi, passion fruit varieties such as Qinmi NO.9, Xiaohuangjin, Tainong NO.1 and Mantianxing were chosen as research objects to evaluate the heat resistance of different passion fruit varieties under continuous high-temperature conditions in the field. 【Methods】When the maximum daily temperature exceeded 32℃ for 5 consecutive days, the flowering, fruit set, and photosynthesis of 4 passion fruit varieties were investigated in Nanning and Guigang orchards. Four-point sampling method was used to randomly select 5 healthy passion fruit plants with the same growth trend in 4 growth directions from 4 regional centers divided by diagonal lines to observe flowering and fruit setting. Simultaneously, the photosynthetic data of passion fruit were obtained by LI-6400XT portable photosynthesis measurement system. Subsequently, statistical software was used to compare the differences in flowering, fruit set, and photosynthesis of 4 passion fruit varieties under continuous high-temperature conditions, and then the heat resistance of 4 passion fruit varieties was evaluated. Meanwhile, the Pearson correlation coefficient was used to explore the potential relationship between flowering, fruit setting, and photosynthesis of 4 passion fruit varieties. 【Results】The results showed that Qinmi No. 9 had the strongest flowering, fruit set, and photosynthesis, followed by Xiaohuangjin and Tainong No. 1, and the weakest was Mantianxing in both orchards. All parameters showed significant differences among varieties except for a few parameters of passion fruit variety that showed significant differences in different passion fruit orchards (p < 0.05). In terms of flowering and fruiting, the average number of branches, flowers, buds, and fruits of Qinmi 9 reached 71.85 nodes per plant, 20.90 flowers per plant, 21.60 buds per plant, and 6.25 fruits per plant, respectively, which were 5.70 nodes per plant, 16.85 flowers per plant, 14.90 buds per plant, and 5.05 fruits per plant more than Xiaohuangjin. It was 11.75 nodes per plant, 19.25 flowers per plant, 18.50 buds per plant, and 5.40 fruits per plant more than Tainong No. 1, and 10.6 nodes per plant, 19.45 flowers per plant, 18.85 buds per plant, and 5.70 fruits per plant more than Mantianxing. For photosynthesis, the net photosynthetic rate (Pn) of Qinmi NO.9 was 21.16 μmol CO2 m-2 s-1, which was 6.78 μmol CO2 m-2 s-1, 11.32 mol CO2 m-2 s-1 and 13.33 μmol CO2 m-2 higher than that of Xiaohuangjin, Tainong NO.1 and Mantianxing, respectively; the stomatal conductance (Gs) was higher by 0.19 mol H2O m-2 s-1, 0.26 mol H2O m-2 s-1 and 0.32 mol H2O m-2 s-1 than Xiaohuangjin, Tainong No.1 and Mantianxing, respectively; the intercellular CO2 concentration (Ci) was 18.14% higher than that of Xiaohuangjin, 58.67% higher than that of Tainong No.1, and 5 times higher than that of Mantianxing, and the transpiration rate (Tr) is 3 times that of Xiaohuangjin, 3.8 times that of Tainong No.1, and 6.1 times that of Mantianxing.【Conclusion】Compared with the other three varieties, Qinmi No. 9 has better heat resistance, and can be used as the main variety promoting in Summer Guangxi, or planted with other varieties, to improve the market contraction caused by yield reduction of other varieties due to the summer high-temperature. It can also enhance Guangxi's regional advantages as main national passion fruit producing area. Meanwhile, Qinmi No. 9 can be used as a fine parent material for future heat-resistance breeding.
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