Effects of different quality light supplement treatments on flower bud development of bayberry (Myrica rubra)

Abstract:【Objective】The process of flower bud differentiation and development determines the flowering period and yield of fruit trees, which has great influence on production. Bayberry (Myrica rubra) is native to China and has important economic value in China. However, it takes a long time from the beginning of floral differentiation to blossom in bayberry. Therefore, it is very important to study the growth and development process of bayberry flower bud. It has been widely reported that light regulates flower bud differentiation and development in plants. The aim of this work was to study the effects of light intensity and light quality on the flower bud differentiation and budbreak processes in bayberry. 【Methods】The two different LED lamps were installed at the top and between two trees in the same row under greenhouse cultivation, in order to compare the difference in their effects on bayberry flower bud development. The spectra of two LED lamps and the greenhouse light intensity were measured to analyze the difference of light intensity and light quality between the two light supplement treatments, the white-light (WL) treatment and red-light (RL) treatment. The differences in color temperature, photosynthetically active radiation (PAR) and wavelength composition of the two light sources can be dis-played by optical analysis. The two treatments had similar peak wavelengths. However, the WL had the highest PAR, and increased the light intensity around the tree mostly. The RL has weaker green light with increased ratio of red to far-red light than WL, so there is a significant difference in color temperature between the two treatments, WL being 3329 K and RL 1531K. In addition, the size and numbers of bayberry flower buds under different treatments were observed and analyzed at the same time. Also, the development degree of bayberry flower buds was studied through morphological and anatomical observations.【Results】In this study, the number of flower buds was significantly increased under the two light supplement treatments. RL had more flower buds than WL. The result suggested that light supplement is beneficial to flower bud differentiation, but different light quality has different effect on flower bud differentiation. Based on microscopic observation, size of flower buds under different treatments was measured. The longitudinal diameter of flower bud was the largest under RL, followed by WL and the smallest in the control. At the same time, both light supplement treatments increased the transverse diameter of flower buds, but there was no significant difference between WL and RL. In addition to physiological indicators of flower bud growth under different treatments, phenological observation was also carried out during the whole budbreak process of the flower buds. The progress of flower bud break was accelerated under both two light supplement treatments. During the blooming of the female flowers, the small stigmas in the upper part of the inflorescence appeared first, followed by those in other parts of the inflorescence. In this study, the flower buds treated with RL had already revealed their Yshaped stigmas and turned bright red in early spring. Meanwhile, the stigmas treated with WL had just stretched out and had a very light red color, while the flower buds of the control had not yet loosened. The anatomy of the flower buds under different treatments were compared with paraffin sections and staining. Most of the floret primordia were formed on the lateral side of the flower buds under RL, and multiple floret primordia were observed on the middle and upper part of flower buds under WL near the top. However, the floral primordia on the lateral side of the flower bud in the control group had not yet been formed at the same stage. The two light supplement treatments were beneficial to flower bud development and advance flowering as they accelerated the formation and development of floret primordia in flower buds.【Conclusion】Light intensity and quality both affect the differentiation and development of bayberry flower buds. The white light has better improvement effect on light intensity, but less effective in promotion of differentiation and development of flower buds than red light, indicating that light intensity may not the main factor affecting the differentiation and development of flower buds. According to the results of this study, the higher proportion of red light and far-red light is most beneficial to the flower bud differentiation and development.