Effect of rain shelter and light supplement on yield, fruit quality and photosynthetic characteristics in passion fruit

Abstract: 【Objective】Passion fruit is native to South America, and because of its unique aroma and flavor, passion fruit is favored in the domestic fruit market in recent years. However, Guizhou and other provinces where the passion fruit is mainly cultivated generally use the open field cultivation, which is susceptible to environmental conditions, so the yield and quality performance of passion fruit is not stable, which affects the economic benefits of passion fruit seriously. As the auxiliary measures of cultivation, rain shelter and light supplement can effectively improve the yield or quality of many vegetables and fruit crops. In order to find the methods which can stabilize performance of passion fruit, in this study, we conducted the rain shelter cultivation and light supplement cultivation, to reveal the effect of the rain shelter and light supplement on the yield and fruit quality of passion fruit, and find the possible contributing causes, so as to provide reference for efficient cultivation of passion fruit.【Methods】The test material was sweet passion fruit, and four treatments were set, including Rain Shelter (RS), Light Supplement (L), Rain Shelter + Light Supplement (RSL) and open field cultivation as the control (CK). The surveyed indexes include: branch length, internode length and thickness, longitudinal fruit diameterand transverse fruit diameter, colour- changing period, average fruit number and weight of individual tree, yield, intrinsic quality of the fruit (titratable acid, total sugar, total free amino acids, vitamin C, total phenols, total flavonoids and β-carotene), content of chlorophyll-a and chlorophyll-b, photosynthetic properties (net photosynthetic rate, transpiration rate, stomatal conductivity and intercellular CO2 concentration).【Results】In contrast to the control, Light Supplement (L) indicated: there was no significant effect on the branch length and internode length, while it could significantly increase the internode thickness by 4%; there was no significant effect on the longitudinal fruit diameter and transverse fruit diameter, but it could accelerate the fruit color change by 3 d (5%); there was no significant effect on the yield, but it could increase the titratable acid content by 3% and the total sugar content by 2%, and the total free amino acids content significantly increased by 12%, the vitamin C content significantly increased by 9%, the total phenols content significantly increased by 13%, the total flavonoids content significantly increased by 38%, the β-carotene content significantly increased by 19%, and the chlorophylla content significantly increased by 11%; there was no significant effect on the chlorophyll-b content, but the net photosynthetic rate significantly increased by 20% , the transpiration rate significantly increased by 8%, the stomatal conductance significantly increased by 19%, and there was no significant effect on the intercellular CO2 concentration. Rain Shelter (RS) indicated: the branch length significantly increased by 19%, the internode length significantly increased by 26%, the internode thickness significantly decreased by 20%, but ther was no significant effect on the longitudinal fruit diameter and transverse fruit diameter, and the fruit color change was delayed by 8 d (14%), yield significantly increased by 20%, the titratable acid content significantly decreased by 14%, the total sugar content significantly decreased by 11%, the total free amino acids content significantly decreased by 7%, the vitamin C content significantly decreased by 6%, the total phenols content significantly decreased by 64%, the total flavonoids content significantly decreased by 43% , the β- carotene content significantly decreased by 37%, the chlorophyll-a content significantly increased by 10%, the chlorophyll-b content significantly increased by 37%, the net photosynthetic rate significantly decreased by 50%, the transpiration rate significantly decreased by 62%, and the stomatal conductance significantly decreased by 55%, the intercellular CO2 concentration significantly decreased by 7%. Rain Shelter + Light Supplement (RSL) indicated: the branch length significantly increased by 19%, internode length significantly increased by 7%, the internode thickness significantly decreased by 6%, while there was no significant effect on the longitudinal fruit diameter and transverse fruit diameter, and the fruit color change was delayed by 4 d (7%), yield significantly increased by 23%, the titratable acid content significantly decreased by 8%, the total sugar content significantly decreased by 10%, the total free amino acids content significantly decreased by 6%, the vitamin C content significantly decreased by 4%, the total phenols content significantly decreased by 50%, the total flavonoid content significantly decreased by 37%, the β-carotene content significantly decreased by 25%, the chlorophyll-a content significantly increased by 19%, the chlorophyllb content significantly increased by 40%, the net photosynthetic rate significantly decreased by 37%, the transpiration rate significantly decreased by 46% , and the stomatal conductance significantly decreased by 51% , but there was no significant effect on the intercellular CO2 concentration.【Conclusion】Light Supplement (L) can significantly improve the leaf photosynthetic characteristics, increase the nutrient contents in fruit, and accelerate the time of fruit color change, but cannot effectively increase the yield. Rain Shelter (RS) and Rain Shelter + Light Supplement (RSL) can significantly increase the yield, but it may lead to the decline of the plant photosynthesis characteristics and the intrinsic fruit quality, and delay the time of fruit color change. All indicators of RSL were better than RS, indi-cating that light supplement can compensate for the influence of insufficient light, but the effect of light source in this test is apparently less than that of natural light. Rain shelter and light supplement should be used according to the actual requirements.