Control Efficiency and Mechanism of Exogenous Melatonin on Postharvest Apple Ring Rot

LIU Fangjie; HAN Xujuan; WANG Yuxuan

doi:10.15933/j.cnki.1004-3268.2026.01.010

Abstract：This study aimed to develop a safe and effective method for controlling postharvest apple ring rot disease caused by Botryosphaeria dothidea.Fuji apple fruits were used as experimental materials in this study.The inhibitory effects of exogenous melatonin on the mycelial growth of the pathogen,as well as its efficacy in controlling postharvest apple ring rot,were evaluated using petri dish antibacterial assays and wound inoculation methods,respectively.Additionally,the activity of cell wall degrading enzymes and the content of cell wall components in apple fruits were analyzed.The results showed that exogenous melatonin effectively inhibited in vitro growth of B.dothidea and significantly enhanced the resistance of postharvest apples to ring rot disease.The most pronounced effects were observed at a concentration of 0.20 mmol/L.At nine days after inoculation,the inhibition rate of mycelial growth of apple ring rot pathogen in vitro culture and the control effect on apple ring rot in postharvest apples treated with 0.20 mmol/L melatonin were 82.19%and 78.53%,respectively.Furthermore,B.dothidea infection significantly increased the activity of cell wall-degrading enzymes in postharvest apples,thereby promoting the degradation of the fruit's cell wall.At seven days post-inoculation,apples treated with 0 mmol/L melatonin exhibited substantial increases in enzyme activities:Carboxymethyl cellulase(Cx),β-glucosidase(β-Glu),filter paperase(FPA),polygalacturonase(PG),polygalacturonase transeliminase(PGTE),and pectin methylgalacturonase(PMG)increased by 333.34%,496.41%,196.35%,666.77%,511.21%,81.87%,respectively,compared to the non-inoculated control(CK).Consequently,there were significant reductions in cellulose,protopectin,and lignin contents by 83.41%,82.39%,and 22.45%,respectively.The treatment with 0.20 mmol/L melatonin significantly reduced the activity of cell wall-degrading enzymes and could effectively alleviate the degradation of the cell wall in apple fruit.At seven days post-inoculation,the activities of Cx,β-Glu,FPA,PG,PGTE,and PMG in the 0.20 mmol/L melatonin treatment were significantly reduced by 25.30%,33.40%,25.51%,37.00%,41.04%,and 17.09%,respectively,compared to the 0 mmol/L treatment.This led to significant increases in cellulose,pectin,and lignin by 353.92%,336.52%and 203.95%,respectively,making them closer to the levels of healthy fruits.In conclusion,exogenous melatonin can effectively inhibit the growth of apple ring rot pathogen and enhance the resistance of postharvest apple fruits to ring rot,with the most effective concentration being 0.20 mmol/L.