Effects of different leaf/fruit ratio on photosynthetic characteristics and fruit quality of Hongmeiren citrus hybrid under protected cultivation

Abstract:【Objective】Reasonable leaf/fruit ratio is an important cultivation index to balance tree vigor, yield and fruit quality. The study on effects of different leaf/fruit ratio on the photosynthetic characteristics and fruit quality of citrus can provide a theoretical basis for improving fruit quality and tree growth.【Methods】6-year-old Hongmeiren citrus hybrid trees grafted on trifoliate orange rootstock under protected cultivation were used as experimental materials. Three different leaf/fruit ratio (LFR) levels (60, 80 and 100) were set respectively through twice thinning. The shoot and leaf growth, leaf chlorophyll content, photosynthetic parameters, yield and fruit quality were determined.【Results】The shoot growth increased with the increase of leaf/fruit ratio. The shoot number and internode length with LFR100 treatment were 1.91 and 1.94 cm, respectively, which were higher than those with LFR60 and LFR80 treatments. However, the leaf growth increased firstly and then decreased with the increase of leaf/fruit ratio. The leaf area, thickness and weight with LFR80 were 291 5.5 mm², 0.34 mm and 1.47 g, respectively, which were higher than those with LFR60 and LFR80. Chlorophyll synthesis in citrus leaves was also affected by leaf / fruit ratio. The chlorophyll content increased significantly with the increase of leaf/fruit ratio. The leaf chlorophyll content with LFR100 in spring- and autumn- growing shoots were 138.56 and 121.96 respectively, which were obviously higher than those with LFR60 and LFR80. The fruit size of citrus was closely related to leaf/fruit ratio. The single fruit weight, longitudinal diameter and transverse diameter with LFR100 were 328.54 g, 88.20 mm and 87.68 mm, respectively, which were significantly higher than those with LFR60 and LFR80. The photosynthetic rate of citrus leaves was also affected by leaf / fruit ratio due to the distribution change of assimilative products. The net photosynthetic rates with LFR60 in spring- and autumn-growing shoots were 14.84 μmol·m^-2 ·s^-1 and 17.26 μmol·m^-2 ·s^-1 , respectively, which were obviously higher than those with LFR80 and LFR100. The transpiration rates with LFR60 in spring- and autumn-growing shoots were 2.14 and 2.03 mmol·m^-2 ·s^-1 , respectively, which were higher than those with LFR80 and LFR100. The stomatal conductance of LFR60 in spring and autumn-growing shoots were 67.87 and 94.33 mmol·m^-2 ·s^-1 , which were obviously higher than that with LFR80 and LFR100. The water use efficiency with LFR60 in spring- and autumn-growing shoots were 0.25% and 0.27%, respectively, which were obviously higher than that withLFR80 and LFR100. The quality of citrus fruit was greatly affected by the leaf / fruit ratio. The total soluble solid contents with LFR60 and LFR80 were 11 and 10.6, respectively, which were significantly higher than those with LFR100. The total acid content with LFR60 was 0.74 g·100 ml-1 , which was significantly higher than that with LFR80 and LFR100. LFR80 had the highest mean value of total soluble solid/acid ratio. The color, edible rate and vitamin C content didn’t exhibit significant change. The fruit quality was comprehensively assessed by using the membership function. The average value of the membership function ranked in a descending order: LFR80 > LFR60 > LFR100.【Conclusion】The LFR80 treatment had higher shoot and leaf growth, chlorophyll content and photosynthetic rates, fruit weight, yield per plant and the best fruit quality. Therefore, in order to ensure high quality and stable yield continuously, the reasonable leaf/fruit ratio of Hongmeiren citrus under protected cultivation should be about 80.