Inhibitory Effects of Bacillus Subtilis M23 Against Citrus Melanose Caused by Diaporthe Citri

Citrus melanose is one of the most prevalent and important fungal diseases worldwide. Owing to the high frequency of chemical fungicides application during disease management, adverse effects emerged in citrus production. Biological control agents (BCAs) are environmental friendly and have become important tools of plant diseases control. In the present study, Bacillus subtilis M23, a strain isolated from healthy citrus leaves, significant suppressed the mycelial growth of Diaporthe citri, the causal agent of citrus melanose. Under greenhouse and field conditions, B. subtilis M23 exhibited good antifungal activities on citrus plants. Among different secondary metabolites produced by M23, the lipopeptides (LPs) possessed excellent antifungal activity against D. citri, and its 50% effective concentration (EC50) was approximately 1.00 and 0.28 μg/mL for mycelial growth and conidial germination inhibition, respectively. Moreover, LPs biosynthetic genes in M23 genome were detected via PCR amplification assays. In addition, LPs extracts drastically suppressed pycnidial formation and ATP biosynthesis in D. citri. Moreover, comparative transcriptome analysis revealed that a significant difference in the expression of genes associated with fungal vacuole, oxidoreductase activity and endopeptidase activity in D. citri when treated with B. subtilis M23, consistent with RNA-seq and qRT-PCR results. Taken together, our data provided important evidence and supported B. subtilis M23 as an novel BCA for managing citrus melanose.