Effects of light supplement on vegetative growth and fruit quality of bayberry (Myrica rubra) in facility cultivation

Abstract:【Objective】There are continuous rainy days in bayberry harvest time of Zhejiang province, which causes low income with high bayberry fruit yield. The bayberry of facility cultivation had a rapid development in recent years, but fruit quality is poor due to insufficient light from color change stage to full maturity. In this study, light supplement technology was developed to enhance tree potential and improve comprehensive quality of bayberry fruit under facility cultivation.【Methods】The 16- year- old Dongkui bayberry trees were tested, which were cultured in a plastic multi-span greenhouse. The total of 4 light sources including LED seedling lamps (50 W, RB 2:1, LYM), growth lamp (50 W, RB 5:1, LSZ), fluorescent seedling lamps (60 W, RB 1:4, YYM) and growth lamps (60 W, RB 1.2:1, LSZ) were selected. Two light supplement level including 1 and 3 lamps every tree were designed, and therefore a total of 8 light treatments were performed, with no light supplement as the control (CK). In the light level of one lamp per tree, the lamp was installed at a horizontal position 1 m vertical above the center point of tree. In the second light level, each of the three lamps was installed at every middle point of the three lines, which connected the two points at the end of 1/3 of the horizontal circle 1 m vertical above the canopy drip-line vertically. The distance among every lamp was equal. The tested trees were ran-domly selected for each light treatment. Each tree served as the experimental plot, and treatment had a total of 3 biological replicates. The distances between trees of different replicates were more than 5 m. Light supplement from 5:00—19:00 every day started from the stone hardening stage to full the maturity of bayberry fruit. The effects of light supplementation on vegetative growth, fruit quality and enzyme activities related to sugar metabolism of bayberry were analyzed.【Results】Light treatments significantly promoted the growth of leaf length, width, thickness and twig length by 6.91%- 18.91% , 6.16%-18.47%, 4.01%-24.56% and 16.35%-64.53%, respectively. The different light treatments had differential effects on fruit size development and coloring. Except for 1YSZ treatment, all of the 1 lamp level treatments promoted fruit development, with an increase of 3.64%-29.92% compared with the control at the stone hardening stage, color break stage and maturity stage, and the single fruit weight increased the most in 1 LYM treatment at maturity stage. All the treatments could improve the fruit quality of bayberry. Except for 3 LYM, the contents of soluble solids in other treatments increased slightly, with an increase range of 1.52%-5.64%. Except for 1 YSZ and 3 LYM, the total sugar content of the other treatments increased slightly in a range of 0.09%-7.66%. Except that the titratable acid content of 1 YYM was reduced by 3.64%, the other treatments had significant acid reduction effects, ranging from 11.52% to 30.91%. Except that the sugar to acid ratio of 1YYM increased slightly (3.90%), the sugar to acid ratio of the other treatments increased significantly (by 17.82%-55.88%). The content of vitamin C in all the treatments increased significantly, with an increase in a range of 13.01%-34.79%, and 1 LYM, 1 LSZ, 1 YSZ and 3 YYM increased the most. The activities of sucrose phosphate synthase and sucrose synthase in fruit were significantly increased by most of the light treatments. Sucrose phosphate synthase activity of 1YYM decreased significantly in the stone hardening stage and mature stage; 3 YYM did not change significantly in stone hardening stage; the sucrose phosphate synthase activity in all the other light treatments increased significantly in stone hardening stage, color break stage and mature stage, with an increase range of 7.28%-49.81%. Sucrose phosphate synthase activity of 1LSZ and 3LSZ increased the most, and the increase range was 21.08%-49.81%, and the increase of the hardcore stage was the most increase. Sucrose synthase activity was significantly decreased by 1 YYM at the color break stage, but significantly increased at the hard core stage, color turning stage and maturity stage by all the other treatments, with an increase range of 3.14%-42.75%. Similar to the effect on sucrose phosphate synthase activity, 1LSZ and 3LSZ showed strongest effect in increasing sucrose synthase activity, with an increase range of 14.70%-42.75%, and the increase at the stone hardening stage was the highest. All the light supplement treatments had no significant effect on twig diameters and chlorophyll contents, and the 3 lamp treatments had no effect or had an inhibition effect on fruit development, among which 3 LSZ and 3 YSZ showed inhibition in the 3 stages, and fruit weight was 6.84% and 15.13% lower than those of the control at maturity stage. Fruit color was not improved by any of the light supplement treatments.【Conclusion】In conclusion, 1 LYM and 1 LSZ treatments had the best effect in increasing single fruit weight and improving comprehensive fruit quality in facility cultivated bayberry.