Abstract:

Different concentrations of paclobutrazol (PP333), chlormequat (CCC) and uniconazole (S3307) were sprayed to investigate the growth dynamics of branches and content of soluble sugar (SS), starch (ST) and non-structural carbohydrates (NSC) in leaves of chestnut (Castanea mollissima ) seedlings, in order to provide a theoretical basis for chemical regulation of chestnut. 【Method】A three-year-old chestnut ‘Yanshanzaofeng’ was used as a test material, and 15% paclobutrazol wettable powder, 50% chlormequat aqueous solution, and 5% uniconazole wettable powder formulation solution were selected as experimental solutions. During flower bud differentiation, we sprayed paclobutrazol (50, 100 and 150 mg/L), chlormequat (100, 150 and 200 mg/L) and uniconazole (30, 60 and 90 mg/L); the whole plant in each treatment was sprayed with clear water as a control (CK) on sunny and windless mornings until the leaves were covered with water droplets without dripping. To study the effects of three plant growth retardants on the growth dynamics of standard and vegetative branches of chestnut seedlings and the content of non-structural carbohydrates in leaves a single-factor completely random block design was used, with a single plant as a plot and five replicates for each treatment. 【Result】① Paclobutrazol, chlormequat and uniconazole significantly reduced the branch length of chestnut seedlings and increased the diameter of branches. The 30 mg/L uniconazole spray was the best for standard shoots. The length of standard shoot was reduced by 24.13% and diameter increased by 26.45% at 90 days after treatment. ② Retardants made the shoots thicker and shorter and could delay the growth of chestnut rootstock, improve the graft survival rate, and facilitate growth after grafting. The 100 mg/L paclobutrazol had the best effect in promoting nutrient shoot growth, making it more effective; the seedling branch increased by 36.63% and length decreased by 17.10%. ③ After spraying the seedlings with retardants, the soluble sugar content in chestnut leaves increased. Among them, the soluble sugar content in the leaves of chestnut seedlings treated with 150 mg/L chlormequat was always at the highest level and was significantly higher than that of the control. It reached the highest level (61.95 mg/g) after 90 days. ④ Different retardant treatments had different effects on the starch content of leaves. The starch content in leaves treated with 100 mg/L chlormequat at 30 days after treatment was always at the highest level and was significantly higher than that of the control. The contents were as high as 1.54 mg/g and 1.51 mg/g respectively. ⑤ All kinds of delaying agents could increase the content of non-structural carbohydrates in chestnut seedlings. After spraying the seedlings with retardants, the total amount of non-structural carbohydrates in the leaves of chestnut seedlings was always at the highest level and was significantly higher than that of the control.【Conclusion】Plant growth retardants made seedlings to grow thick, be shortened, and inhibited the growth of chestnut, improving the graft survival rate and facilitating the growth after grafting. Among the retardants, 30 mg/L uniconazole had the best treatment effect on standard shoots, while 100 mg/L paclobutrazol had the best effect in promoting the nutrient shoot growth. The application of retardants to chestnut seedlings was beneficial in the carbon supply of leaves. In this study, 200 mg/L chlormequat was the best treatment. Thus, in applying retardants for the cultivation of chestnut, different types and mass concentrations of retardants should be reasonably selected based on the purpose of production.

Key words: plant growth retardant, chestnut (Castanea mollissima ), branch, leaf, soluble sugar, starch, non-structural carbon hydrate