Comparative biocontrol efficacy and mechanisms of Bacillus tequilensis application methods against anthracnose caused by Colletotrichum fructicola in Camellia oleifera

Camellia oleifera anthracnose, primarily caused by Colletotrichum fructicola , leads to significant economic losses. As a sustainable alternative to chemical pesticides, this study investigated the biocontrol efficacy of Bacillus tequilensis DZY 6715 against this disease and elucidated the difference by different application methods: foliar spray and root irrigation. Results indicated that DZY 6715 application significantly suppressed disease incidence and lesion expansion, with root irrigation proving superior to foliar spray, achieving a biocontrol efficacy of 53.62 %. This significantly stronger protection resulted from a multi-layered induced resistance more effectively triggered by root irrigation compared to foliar spray. It systemically enhanced physical barriers by triggering stomatal closure, increasing wax layer thickness, and optimizing leaf anatomy. Root irrigation more potently activated the phenylpropanoid pathway, leading to elevated activities of phenylalanine ammonia-lyase (PAL), cinnamic acid-4-hydroxylase (C4H), 4-coumarate: coenzyme A ligase (4CL), cinnamyl alcohol dehydrogenase (CAD), polyphenol oxidase (PPO) and peroxidase (POD) and the accumulation of lignin, cellulose, and hemicellulose. Additionally, root irrigation reconfigured the phyllosphere microbiome to a greater extent, enhancing microbial community stability and network complexity, and suppressing pathogens.