Effects of exogenous melatonin on growth and fruit quality of peach (Prunus persica)

Abstract:【Objective】The object of this study was to investigate the effects of exogenous melatonin (MT) on the growth and fruit quality of peach (Prunus persica).【Methods】The early ripe peach (‘Zao-mi’) was used as the materials, and different concentrations of MT were sprayed on the leaves of peach during the fruit expansion period. The new branches growth (stem length and stem diameter), photosyn-thetic physiology [photosynthetic pigment content (chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid), antioxidant enzyme (superoxide dismutase and catalase) activity, osmotic substance con- tent (malondialdehyde and soluble protein)] and fruit quality [related metabolic enzyme (phenylalanine ammonia lyase, ascorbate peroxidase, lipoxygenase, and polyphenol oxidase) activity, appearance quali-ty (single fruit weight, fruit longitudinal diameter, fruit diameter, fruit firmness and fruit shape index),internal solution (vitamin C, soluble solids and titratable acid) content and different sugar component (total sugar, sucrose, fructose, sorbitol and glucose) content] of peach were determined during the mature period.【Results】50-150 µmol·L^-1 MT treatment promoted the new shoot growth of peach by in-creasing the stem length and stem diameter, while 200 µmol·L^-1 MT treatment decreased the new shoot growth. The different concentrations of MT had different effects on the contents of chlorophyll a, chlo-rophyll b, total chlorophyll, and carotenoid in peach leaves. The concentrations of 100 and 150 µmol·L^-1 MT enhanced the chlorophyll a/b of peach leaves, while the concentrations of 50 and 200 µmol·L^-1 MT reduced or had no significant effect on the chlorophyll a/b. When the MT concentration was 150 µmol·L^-1,the superoxide dismutase activity of peach leaves enhanced, however the other MT concentrations re-duced that compared with the control. The concentrations of 50-100 µmol · L^-1 MT enhanced the cata-lase activity of peach leaves, the other treatments reduced the catalase activities. The concentration of 50 µmol · L^-1 MT also increased the contents of malondialdehyde and soluble protein in peach leaves, and 100, 150, and 200 µmol · L^-1 MT decreased these two osmotic substances contents. Different MT concentrations enhanced the phenylalanine ammonia lyase, ascorbate peroxidase and lipoxygenase ac- tivities of peach fruits, and reduced the polyphenol oxidase activity. The order of the effects of MT on the phenylalanine ammonia lyase activity was 200 µmol·L^-1 > 150 µmol·L^-1 > 50 µmol·L^-1 > 100 µmol·L^-1 >0 µmol·L^-1, on the ascorbate peroxidase activity was 150 µmol·L^-1 > 100 µmol·L^-1> 50 µmol·L^-1 > 200 µmol·L^-1> 0 µmol·L^-1, on the lipoxygenase activity was 150 µmol·L^-1 > 100 µmol·L^-1> 50 µmol·L^-1>200 µmol·L^-1> 0 µmol·L^-1, and on the polyphenol oxidase activity was 0 µmol·L^-1 > 200 µmol·L^-1 >100 µmol·L^-1 > 150 µmol·L^-1> 50 µmol·L^-1. The concentrations of 100 and 150 µmol·L^-1 MT in-creased the single fruit weight of peach fruits by 13.57% and 14.62%, respectively, compared with thecontrol, and the concentrations of 50 and 200 µmol·L-1 MT decreased the single fruit weight. The con-centrations of 100 and 150 µmol·L^-1 MT increased the longitudinal diameter and diameter of peach fruits and decreased the fruit firmness, while the concentrations of 50 and 200 µmol·L^-1 MT decreased fruit longitudinal diameter and transverse diameter and increased the fruit firmness. There were no sig-nificant differences of fruit shape index among the fruits treated with different MT concentrations. The concentrations of 100 and 150 µmol·L^-1MT increased the contents of Vitamin C and soluble solids in peach fruit, while the concentrations of 50 and 200 µmol·L^-1 MT decreased or had no significant effects on these items. The concentrations of 100 and 150 µmol·L^-1 MT increased the Vitamin C content by 31.40% and 19.69%, respectively, and increased the soluble solids content by 18.83% and 21.37%, re-spectively, compared with their respective control. The concentrations of 50 and 200 µmol·L^-1 MT de-creased the content of titratable acid in peach fruit by 25.28% and 19.06%, respectively, while other con-centrations of MT had no significant effects on the content of titratable acid.The concentrations of 50,100 and 200 µmol·L^-1 MT decreased the total sugar content in peach fruits, and 150 µmol·L^-1 MT had no significant effects. The concentrations of 100 and 150 µmol·L^-1 MT increased the sucrose content in peach fruits by 10.11% and 17.04% , respectivel and other treatments decreased the sucrose content. With the increase of MT concentration, the fructose content in peach fruit increased when the MT con-centration was not higher than 100 µmol·L^-1, and decreased when the MT concentration was higher than 100 µmol·L^-1, with the maximum at 100 µmol·L^-1 MT (increased by 21.37% compared with the control). 100 µmol·L^-1 MT increased the sorbitol content in peach fruits by 24.11%. The concentrations of 100 and 150 µmol·L^-1 MT decreased the glucose content in peach fruits by 37.25% and 26.16%, re-spectively, and other treatments increased the glucose content.【Conclusion】MT could promote the shoot growth of peach by improving the resistance, increase the yield of peach by increasing the single fruit weight, and improve fruit quality of peach fruits by improving the sugar component content.