Abstract:

Objective: In this study, the effects of paclobutrazol (PP₃₃₃) and chlormequat (CCC) on the growth of chestnut young branches and leaves, and carbon-nitrogen metabolism of leaves were investigated, which aims to provide a scientific basis for comprehensive understanding of the effects of plant growth retardants on the growth of chestnut saplings and their application. Methods: The 6-year-old Chinese chestnut variety Castanea mollissima 'Yanshanzaofeng' was selected as the test material. Two kinds of retardants, paclobutrazol and chlormequat, were sprayed on the leaves during the rapid growth period of branches. The retardant concentrations were set as 100, 200 and 300 mg·L^-1, with water served as the control (CK). After treatment, the growth index of mother branch, fruit branch, vegetative branch, single leaf area, leaf length-width ratio, leaf water content, relative chlorophyll, carbon and nitrogen metabolite content were regularly measured, and those collected data were used to explore the effect and application feasibility of the two kinds of retardants. Results: The main results were as follows:1) Paclobutrazol and chlormequat significantly inhibited the longitudinal growth of mother branch, fruit branch and vegetative branch of young chestnut trees, and promoted the basal diameter, and there were significant (P < 0.05) differences of all treatments compared with the control. For fruit branches, the effect of spraying 200 mg·L^-1 chlormequat was the most significant on length growth, and the growth was about 81% less than the control. The growth of base diameter of fruit branch was significantly increased by spraying 100 mg·L^-1 chlormequat, and the growth was about 74% higher than the control. 2) Paclobutrazol and chlormequat significantly reduced the single leaf area and increase the ratio of leaf length to width, leaf water content and relative chlorophyll content. Among treatments, spraying 200 mg·L^-1 chlormequat reduced the single leaf area by 11% compared with the control, and increased the relative chlorophyll content by 10.28% compared with the control. Spraying 300 mg·L^-1 paclobutrazol significantly increased the content of leaf water, with 28% higher than the control. 3) Paclobutrazol and chlormequat were able to significantly promote the accumulation of carbon and nitrogen metabolites of young chestnut leaves. Compared with the control, spraying 300 mg·L^-1 paclobutrazol or 100-200 mg·L^-1 chlormequat significantly increased the content of soluble sugar, total nitrogen and the ratio of carbon to nitrogen. Conclusion: Based on the comprehensive analysis of the effects of two kinds of retardants on branch growth and leaf physiological indexes, it is found that spraying 100-200 mg·L^-1 chlormequat during the rapid growth period of young trees can significantly promote the diameter of mother branch and fruit branch, and inhibit their elongation growth, and also effectively promote the accumulation of carbon and nitrogen metabolites in leaves.

Key words: chestnut, retardant, branch growth, carbon-nitrogen metabolism