Effects of fruit load on the composition of branches, fruit quality and yield of ‘Regal Gala’ apple

Abstract:【Objective】The study explored the effects of fruit load on the composition of branches, fruit quality and yield in the high-spindle-shaped apple trees of‘Regal Gala’cultivar grafted on Malus hupe- hensis Rehd. rootstock in order to determine the appropriate fruit load level and to provide theoretical reference for the selection of reasonable yield in production.【Methods】The materials were 7 to 8-year- old trees of‘Regal Gala’apple. Four load levels were designed in this experiment. The development of the trees, the number and proportion of different types of branches, fruit quality and yield and other indi- cators were investigated.【Results】With the increase in fruit load, tree height, new shoot length and to- tal number of branches decreased. The number of spur shoots increased significantly, and the numbers of medium shoots (15-30 cm) and long shoots (30-60 cm and ≥60 cm) decreased rapidly, resulting in a significant reduction in the total number of branches. In 2015, the number of spur shoots in treatmentI was significantly higher than in the other treatments, and in 2016 the number of spur shoots in treat- ment IV was the highest, which was significantly different from that of treatment I and treatment II. Due to high fruit load, tree resources were allocated to fruit development with reduced supply to branch growth. As a result, tree vigor was significantly weakened, and thus the total number of branches signifi-cantly reduced. The canopy width in east-west direction was higher than that in the north-south direc- tion in 2015 and 2016. The coverage rate in treatment III was the highest in 2015, while it was highest in treatment I and lowest in treatment IV in 2016. To clarify the effect of fruit load on the growth of branches in the canopy, the numbers and proportions of different branch types were investigated in 2016. The results showed that the number and proportion of branches were differentially affected by fruit load at different canopy heights. The proportion of spur shoots (< 5 cm) was the highest. Within the same canopy height, with the increase in fruit load, the proportion of spur shoots (< 5 cm) increased gradually with the increase in fruit load, while the proportion of long shoots (30-60 cm and ≥60 cm) de- creased gradually. The canopy height of 1.0-3.0 m had the highest branches distribution. It was found that fruit load affected not only the internal quality of the fruit. With the increase of fruit load, the fruit weight and vitamin C content gradually decreased, while the fruit firmness increased gradually. Fruit color values (L, a and b) in treatment III were higher than the other treatments. Brightness of the fruit from the upper canopy was significantly higher than from the lower canopy. There was no significant difference in fruit firmness between treatment III and treatment II in 2015, or between treatment III and treatment IV in 2016. Fruit soluble solid content in treatment III was the highest in both seasons and the lowest in treatment IV. The titratable acidity in treatment II and treatment III was similar in 2015 and significantly higher than in the other treatments. It was the highest in treatment III in 2016. The canopy height of 2.0-3.0 m was the major part of yield, which accounted for 30 percent of the total yield. The fruit yield in treatment IV in all canopy heights was the highest. When the fruit load was 41.25×104 per hm2(treatmentIV),thehighestyieldin2015and2016was5.79×104 kg·hm-2and6.19×104 kg·hm-2,re- spectively【. Conclusion】TreatmentIII(28.87×104 perhm2)wastheappropriatefruitloadfor7-8year old high-spindle-shaped trees of‘Regal Gala’on Malus hupehensis Rehd. rootstock. The tree devel- oped well with a reasonable branch structure, good yield, fruit appearance and intrinsic quality.