Effects of continuous high-temperature on flowering and fruit-setting habits and photosynthesis of four passion fruit varieties

Abstract: 【Objective】The study aimed to provide theoretical reference for the rapid screening of breeding materials of passion fruit for high- temperature tolerance and summer planting layout in Guangxi.【Methods】The passion fruit varieties Qinmi No. 9, Xiaohuangjin, Tainong No. 1 and Mantianxing were chosen as research material. When the maximum daily temperature exceeded 32 ℃ for 5 consecutive days, the flowering, fruit setting rate and photosynthesis of the 4 passion fruit varieties were investigated in the orchards of Nanning and Guigang. The four-point sampling method was usedto 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, the statistical software was used to compare the differences in flowering, fruit setting, and photosynthesis of 4 passion fruit varieties under continuous high-temperature conditions, and then the heat resistance of the 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 the 4 passion fruit varieties.【Results】Qinmi No. 9 had the strongest flowering, fruit setting, and photosynthesis, followed by Xiaohuangjin and Tainong No. 1, and Mantianxing had the weakest performance in both orchards. All parameters showed significant differences among varieties except for a few parameters that showed significant differences between the different orchards (p<0.05). Qinmi 9 had more nodes, flowers, buds, and fruits than Xiaohuangjin, Tainong No. 1 and Mantianxing. Qinmi No. 9 had higher net photosynthetic rate (Pn) Xiaohuangjin, Tainong No. 1 and Mantianxing. Qinmi 9 had higher stomatal conductance (Gs) than Xiaohuangjin, Tainong No. 1 and Mantianxing. Qinmi 9 had higher intercellular CO2 concentration (Ci) than Xiaohuangjin, Tainong No. 1 and Mantianxing, and had higher transpiration rate (Tr) Xiaohuangjin, Tainong No. 1 and Mantianxing.【Conclusion】Compared with the other three varieties, Qinmi No. 9 has stronger heat resistance, and could be used as main variety to grow in Guangxi, or planted with other varieties. It also could be used as a fine parent material for future heat-resistance breeding.