Inhibition of green mold disease in mandarins by preventive applications of methyl jasmonate and antagonistic yeast Cryptococcus laurentii

• Preventive activity of MeJA combined with C. laurentii in inhibiting green mold in citrus fruit inoculated with Penicillium digitatum was better than MeJA or antagonistic yeast applied alone.
• MeJA increased the population growth of C. laurentii in citrus fruit wounds.
• MeJA and C. laurentii activated the PPO, POD and CAT activities of citrus fruit.
• MeJA and C. laurentii induced a rise in the mRNA expression level of PR5 of citrus fruit peel.

The objective of this study was to evaluate the preventive activity of methyl jasmonate (MeJA) alone and in combination with antagonistic yeast in suppressing green mold decay in citrus fruit, and to explore the mechanisms involved. At 100 μmol/L, MeJA inhibited disease incidence and lesion diameter of mold decay compared with the control (P < 0.05) The preventive application of Cryptococcus laurentii at 1 × 108 cells/mL combined with 100 μmol/L MeJA reduced green mold incidence compared to the control and the other treatment groups (P < 0.05) when tested in wounded citrus fruit inoculated with Penicillium digitatum. MeJA and C. laurentii induced higher activity of polyphenol oxidase, peroxidase and catalase than control. Moreover, treatment with MeJA and C. laurentii induced a rise in the mRNA expression level of PR5 (pathogenesis-related protein family 5), which was stronger than in the single-treatment groups and the control. In addition, 100 μmol/L MeJA improved the rapid proliferation of C. laurentii in citrus fruit wounds. This combined treatment can induce natural resistance and stimulate the proliferation of antagonistic yeast on the fruit surface.