Relationships between distribution of relative light intensity and qualityin‘Yueshuai’apple with different fruit loads

Abstract:【Objective】Sparse planting with vigorous large canopy used to be the major planting system inapple orchards around the Bohai Gulf. After the trees entered the full bearing age, they had numerousbranches and canopy became dense, which reduced fruit quality. Therefore, there is an urgent need to findout the effect of fruit load on light condition and fruit quality. We took‘Yueshuai’, a hybrid of‘Golden de⁃licious’בStarking delicious’bred by Liaoning Research Institute of Pomology, as the experiment materi⁃al to study the effect of fruit load on the amounts of branches and buds, light conditions and fruit quality.【Methods】For measurement of light intensity, we used gird method, where the canopy was divided intolayers of 0.5 meter height per side. A TSE-1332 type digital illumination meter was used to measure lightintensity at different layers and orientations. For the measurement of fruit color values, we needed to takesamples at different canopy positions, including < 1.0 meter, 1.0 to 2.5 meters and >2.5 meters in verticaldirection and at the center (less than 1.0 meter from the trunk) and periphery (1.0-2.5 m from the trunk)in horizontal direction. A CR 400 colorimeter of Monolta Konica was used to measure fruit colors at different fruit positions. A GY-1 handheld sclerometer was used to measure rigidity and a PAL-1 digital refractometer made in Japan was adopted to measure the content of soluble solids. Sodium hydroxide titrationwas applied to quantify acid content and 2,6-dichlorophen indophenols method for vitamin C content. Sta⁃tistical software such as Origin 8.0, excel and DPS were used to process the experimental data and onewayanalysis of variance to test the significance of differences among treatments.【Results】Treatment IIIwith a fruit load of 1 881.81 had the largest number of branches, followed by treatment II with 1 015.65fruit and treatmentⅠwith 834.96 fruit. The branch and bud numbers and the proportions of long, mediumand short shoots (0.35∶0.14∶1) were suitable for producing high-class fruit in treatment II. Different fruitload treatments differed in distribution of light intensity. Treatment Ⅱ was good in light conditions withthe best exposure area that received 35% to 75% of full sun reached at least 60% of the canopy area. Thetrees thus had a high potential to produce a high crop with good quality and a reasonable load. Fruit loadhad an effect on the color parameters of fruit. The fruit color reflected by parameters in both the canopy pe⁃riphery (1.0-2.5 m) and the canopy center in treatment II was better than the other treatments. Compari⁃son of fruit quality between fruit loads in different canopy positions showed that treatment II with a medi⁃um fruit load had the best fruit quality in canopy periphery (1.0-2.5 m) and middle periphery, where average fruit weight was 328.75 gram, fruit firmness 8.65, soluble solid content 12.99%, and acid content0.330% with a nice looking in treatment II.【Conclusion】A medium fruit load (106.63 kg per plant) intreatment II had the advantages of even fruit distribution in canopy, high percentage of superior qualityfruit, and high and stable yield. Fruit quality of the apples had a close relationship with fruit load in thecanopy, which directly influenced the size, soluble solids, sugar acid ratio, VC and surface color of thefruit and the dry matter production in the trees. Meanwhile, medium fruit load overcame biennial bearing.