High-temperature response and heat tolerance evaluation of different passion fruit varieties （lines）

【Objective】 This study aimed to investigate the responses of different passion fruit varieties （lines） to high temperature and conduct comprehensive evaluation of their heat tolerance，so as to provide theoretical references for high and stable yield cultivation and breeding of heat-tolerant varieties for passion fruit. 【Method】 Using 12 passion fruit varie-ties （lines） as experimental materials，and a two-factor split-plot experimental design was adopted： the main plot factor was temperature， for which a high-temperature treatment and an open-field control were set； variety （line） was the split-plot factor. Seven physiological indicators of leaf leaf relative conductivity， pollen germination rate， soluble protein content， soluble sugar content， catalase （CAT） activity， superoxide dismutase （SOD） activity， and peroxidase （POD） acti-vity and two agronomic traits （fruit set per plant and fruit setting rate） were determined； and the correlations among the nine indicators were analyzed. The comprehensive evaluation and cluster analysis of heat tolerance of the 12 passion fruit varieties （lines） was performed using membership function method. 【Result】 After 40 d of high-temperature treatment and compared with control， the SOD activity in passion fruit leaves significantly decreased （P<0.05， the same below）， the POD activity extremely significantly decreased （P<0.01，the same below）， and the CAT activity extremely significantly increased； no significant differences were observed in relative conductivity， soluble sugar content， and soluble protein content between the high-temperature treatment and the control （P>0.05）. After 40 d of high-temperature treatment， the average pollen germination rate， average fruit set per plant within 0-40 d of treatment，and average fruit setting rate at full bloom of the tested passion fruit varieties （lines） were 4.55%， 45.38%， and 32.27% lower than those of the control， respectively. According to comparison results among the varieties， P5， H3， and H36 had pollen germination rates of 78.88%-82.42%， which were significantly higher than those of other varieties （lines）； while P1， DN， and Xiaji had pollen germination rates of just 31.33%-40.58%， significantly lower than those of other varieties （lines）. During 0-40 d of high-temperature treatment， fruit set per plant of MT and H36 were 12.00 and 7.57， while the fruit setting rates of H3 and MT at full bloom were 66.39% and 51.14% respectively， which were significantly higher than those of other varieties （lines）. Correlation analysis showed that fruit setting rate was significantly positively correlated with SOD activity， POD activity， and pollen germination rate. Based on the comprehensive evaluation value of heat tolerance （D）， the heat tolerance of the 12 passion fruit varieties （lines） was in the order of H36 > MT > Tainong No. 1 >H3 > P5 > P7 > Xiaji> P1 > Donghuimi > Yuanxiao > Huangyou No. 2 > DN. Cluster analysis results showed that the 12 varieties （lines） were divided into four groups， among which H36 and MT exhibited the strongest heat tolerance， while Huangyou No. 2 and DN showed the poorest. 【Conclusion】 Pollen germination rate， fruit setting rate， and fruits set number per plant can be used as comprehensive evaluation indicators for heat tolerance of different passion fruit varieties （lines）. Two varieties （lines） with the strongest heat tolerance，H36 and MT， are screened.