Effects of fruit loads on photosynthetic characteristics of peach leaves and fruit quality

Abstract:【Objective】Fruit thinning technology has been widely used in fruit production for overcoming the phenomenon of biennial bearing, maintaining stable yield and improving fruit quality. The amount of fruit loads directly determines the sink - source ratio of trees, and then affects the growth and development of vegetative and reproductive organs of the fruit trees. The study aimed to evaluate the effects of different fruit loads on chlorophyll content, net photosynthetic rate, photosynthetic compound output in the leaves, fruit quality and growth and development of peach trees in order to provide a theoretical basis for improving fruit quality and tree growth and development.【Methods】9 years old Xiahui 8 peach trees were used as experimental materials, and the experiment included 5 treatments: T1 (keeping 100% fruits on the tree), T2 (keeping 75% fruits on the tree), T3 (keeping 50% fruits on the tree), T4 (keeping 25% fruits on the tree) and T5 (keeping 0 fruits on the tree, control). The chlorophyll content, net photosynthetic rate and photocompound content of the mature leaves were measured in early May (2 d after fruit thinning), early June (fruit core-hardening period), late July (10 d before harvest) and early August (2 d after harvest). In addition, two days after fruit thinning, 10 fruits (except for the control) were labeled in the middle periphery of each tree, and the longitudinal, transverse and lateral diameters of the fruits were measured every 10 days until the fruits matured. At the fruit maturity stage, 30 fruits were uniformly collected for each treatment (10 fruits for a repeat, three repeats) for evaluation of the fruit quality. After the leaf fall, the number of flower and leaf buds, internode length of branches and the number of fruit-bearing branches for different treatments were investigated. All data were statistically analyzed.【Results】On 2 d after fruit thinning, different tree loads had no significant effect on the leaf chlorophyll content, but the leaf chlorophyll content decreased with the decrease of the tree loads in the last three periods. The net photosynthetic rate of the control was relatively higher in the four periods. On 2 d after fruit thinning and in the fruit core-hardening period, the net photosynthetic rate of the leaves of the T1 treatment was at the highest level, while the T2 was at the lowest level. On 10 d before harvest, the net photosynthetic rate of the leaves of the T2 treatment was the highest, and the T1 treatment the lowest. On 2 d after harvest, the net photosynthetic rate of the leaves increased with the increase of the fruit loads. The water use efficiency and apparent CO2 use efficiency of the leaves decreased with the decrease of the fruit loads, while the change trend of apparent light use efficiency of the leaves was consistent with the trend of net photosynthetic rate for different fruit loads. In the four periods, the contents of soluble sugar and sugar alcohol in the leaves increased with the increase of the fruit loads. In terms of fruit quality, the fruit size, single fruit weight, soluble solid content, sugar-acid ratio, soluble sugar and sugar alcohol content were significantly increased with the reduction of the fruit loads, the sugar-acid ratio was the highest and the fruit flavor was the best when the fruit load was 50% (T3 treatment). In addition, with the increase of the fruit loads, the yield per 666.7 m2 increased, the proportion of the leaf buds increased while the proportion of flower buds decreased, the number of short fruit branches increased ,and the long fruit branches decreased.【Conclusion】In the present study, under the treatment of 50% fruit retention, the photosynthesis capacity and chlorophyll content of the peach leaves were at a high level in the four periods, and soluble sugar content in the leaves was at a low level in the latter two periods, indicating that the leaves would have a higher ability to produce and export carbohydrates when the fruit load was 50% , and they would have a relatively higher source strength. The contents of sucrose, glucose, fructose and total sugar in the fruits were all at the highest levels when the fruit load was 50%, indicating that fruits would have a strong ability to absorb and transform carbohydrate and would have a higher sink strength. When the peach trees were at 50% fruit load, the sugar - acid ratio was relatively higher, and the fruit taste was good. The proportion of flower buds, leaf buds and fruit branches was relatively balanced when the fruit load was 50% , which would be beneficial to the growth and development of the trees in the next year. We recommend that the adult peach tree of Xiahui 8 would have a high yield with quality fruits when the thinning rate be 50% in the normal condition.