Effect of Metschnikowia pulcherrima and methyl jasmonate on apple blue mold disease and the possible mechanisms involved

Metschnikowia pulcherrima alone and in combination with methyl jasmonate [MeJA] was applied for control of blue mold of apple caused by Penicillium expansum. In vitro, MeJA at different concentrations had no direct effect on the pathogen. In vivo, both M. pulcherrima (1×108 cell ml-1) and MeJA, as a stand-alone treatment, significantly reduced the lesion area of blue mold decay in apple. The combination of MeJA at 100 μmol l -1 and antagonistic yeast (1×108 cell ml-1) was a more effective approach to reduce the lesion diameter of blue mold decay of apples than the application of MeJA or M. pulcherrima separately after incubation for 15 and 50 days at 20°C and 4°C, respectively. In addition, MeJA increased the population of M. pulcherrima in the wounds of the apple fruit. The activity of the defense enzyme peroxidase was enhanced by MeJA and yeast treatments, and the level of total phenolic content in MeJA and yeast-treated fruit was also higher than that in control fruit. These results suggest that MeJA was effective in reducing decay and might enhance disease resistance in apple fruit by increasing defense enzyme activity and levels of antimicrobial phenolic compounds.