Isolation and Identification of the Pathogens of 'East Red' Kiwifruit Soft Rot and Its Control Effect by Melatonin

To clarify the species of the pathogens of soft rot of 'East Red' kiwifruit and the effect of melatonin on its control, using naturally disease 'East Red' kiwifruit as test material, the pathogenic bacteria of soft rot were isolated and cultured using a tissue isolation method. The pathogenic bacteria isolated were tested for pathogenicity according to Koch's rule, and identified based on fungal morphological identification and rDNA-ITS sequence analysis. The effect of melatonin at different concentrations (0, 100, 300 and 500 μmol/L) on the control of the two pathogenic strains isolated was also investigated. The results showed that Diaporthe phaseolorum and Botryosphaeria dothidea were the main pathogenic bacteria causing soft rot of 'East Red' kiwifruit during storage. The in vitro inhibition test showed that melatonin significantly inhibited the mycelial growth of both pathogens (P<0.05). At 5 d of incubation, the inhibition rates of 500 μmol/L melatonin were 71.22% and 63.34% for Diaporthe phaseolorum and Botryosphaeria dothidea, respectively. At the meanwhile, melatonin was effective in controlling the expansion of soft rot lesions under damage inoculation. At 5 d of damage inoculation, the diameter of fruit spots after the inoculation of Diaporthe phaseolorum and Botryosphaeria dothidea with 500 μmol/L melatonin treatment was only 37.40% and 45.50% of the control group, respectively. It showed that melatonin had potential application value for the control of soft rot pathogens of 'East Red' kiwifruit.