Screening of Biocontrol Bacillus Strains Against Bayberry Twig Blight Disease and Investigation of Their Disease-Suppressive Mechanisms

Bayberry twig blight disease is one of the major diseases restricting the sustainable development of the bayberry industry, causing serious yield and quality losses. At present, chemical control remains the main strategy for disease management; however, its long-term application may lead to pesticide resistance and ecological risks. Therefore, exploring stable, safe, and efficient biocontrol microbial resources is of great significance for establi shing sustainable disease management strategies.

This study aimed to screen endophytic Bacillus strains with antagonistic potential from bayberry trees, construct a synthetic community (SynCom), and systematically evaluate its disease control efficacy and associated functional characteristics against bayberry twig blight disease.

Endophytic Bacillus strains were isolated from the stems, branches, and leaves of healthy and diseased bayberry plants using tissue isolation methods. Antagonistic activity against Pestalotiopsis versicolor XJ27, the pathogen of bayberry twig blight disease, was initially screened using dual-culture assays. Seven strains with stable inhibitory activity were further selected through detached leaf assays and subsequently assembled into a synthetic community (SynCom). The disease control efficacy of single strains and the SynCom was evaluated under greenhouse conditions. In addition, the potential antagonistic traits of the strains were investigated by observing hyphal morphological changes of the pathogen and assessing extracellular enzyme activities, siderophore production, biofilm formation, and the inhibitory effects of crude lipopeptide extracts.

The single Bacillus strains exhibited disease control efficacy ranging from 24.67% to 50.67%, whereas the SynCom treatment achieved a higher control efficacy of 61.33%, which was 21.04%-148.60% higher than that of single strain treatment (calculated based on the control efficacy of single strain). Morphological observations revealed abnormal hyphal features of the pathogen, including swelling, distortion, and fragmentation, after treatment with biocontrol bacteria. Further analyses demonstrated that all strains exhibited varying capacities for extracellular enzyme production, siderophore secretion, and biofilm formation, and their crude lipopeptide extracts exhibited concentration-dependent inhibitory effects on the pathogen, suggesting that multiple antagonistic factors may synergistically contribute to disease suppression.

Bayberry trees harbor valuable endophytic Bacillus resources with potential biocontrol applications. The constructed SynCom exhibited superior disease control efficacy compared with individual strains, highlighting its potential for managing bayberry twig blight disease. This study provides experimental evidence and microbial resources for developing sustainable and microbiome-based disease control strategies for bayberry.