Combined application of methyl jasmonate and Bacillus subtilis LLCG89 suppresses blue and green mold of lemon (Citrus limon L.)

Background: Bacillus species produce antimicrobial lipopeptides (LPs) and methyl jasmonate (MeJA) induces resistance in harvested fruits against postharvest pathogens. However, there is limited evidence of the combined efficacy of Bacillus LPs and MeJA to suppress postharvest diseases.

Results: This study presents the combined effect of Bacillus LPs and MeJA to suppress P. digitatum and P. italicum associated with green and blue mold of lemon. Eight Bacillus strains were screened in a direct antagonism plate assay, where Bacillus subtilis LLCG89 and B. atrophaeus HFZ23 exhibited the highest inhibition of both molds. Subsequently, in an in vitro assay, LPs extracted from LLCG89 demonstrated the highest antifungal activity against both pathogens compared to HFZ23. When combined with MeJA, LLCG89 LPs reduced the lesion diameter and disease incidence of blue and green mold on lemon fruit. Co-application of MeJA and LLCG89 LPs decreased the levels of MDA, H₂O₂, and electrolyte leakage compared to single treatments and controls. Furthermore, treatment with MeJA and LLCG89 LPs increased the activities of defense enzymes including SOD, CAT, POD, PPO, CHI, GLU, APX, and PAL with peak activity between 48 to 72 h. The co-application of MeJA and LLCG89 LPs showed the highest enzyme activity compared to the control. Postharvest quality analysis indicated that co-application of LLCG89 LPs and MeJA showed little impact on fruit quality.

Conclusion: The findings of our study highlight the potential of Bacillus-derived LPs and MeJA as effective tools for managing the Penicillium decay of lemons by maintaining fruit quality. © 2025 Society of Chemical Industry.