Biofilm-forming of Bacillus tequilensis DZY 6715 enhanced suppression the Camellia oleifera anthracnose caused by Colletotrichum fructicola and its mechanism

Recently, Bacillus species have attracted significant attention for the biological control of many fungal diseases and the ability of Bacillus biofilm formation makes a vital impact on plant disease control. In the present study, we found that Bacillus tequilensis wild-type strain WDZY 6715 which formed a robust biofilm, could significantly hinder the mycelial growth of Colletotrichum fructicola in vitro and in vivo with an inhibition rate of 65.70 % and a disease index of 30.55 on the 10th day. In comparison to the mutant strain, the wild-type strain WDZY 6715 had a stronger ability to secrete extracellular hydrolases including chitinase (CHI) and β-1,3-glucanase (GLU), and the formation of biofilms enhanced its colonization ability on the host. Furthermore, we also analyzed the anatomical characteristics of camellia oleifera leaves treated with wild-type and mutant strains, while the wild-type strain significantly increased leaf thickness, upper epidermis, spongy tissue, palisade tissue and leaf structural compactness (CTR), thus strengthening the physical barrier of C. oleifera. Meanwhile, the wild-type strain WDZY 6715 obviously elevated the activity of defense-related enzymes, which included PAL, C4H, 4CL, CAD, LA, PPO and POD, and stimulated the synthesis of total phenols and lignin. Taken altogether, these results suggest that biofilm formation is crucial to Bacillus tequilensis DZY 6715 against anthracnose pathogen in C. oleifera.