Increasing Light Intensity Enhances Bacillus amyloliquefaciens PMB05-Mediated Plant Immunity and Improves Biocontrol of Bacterial Wilt

Bacterial wilt is a highly destructive disease affecting a wide range of crops, with no effective chemical control methods currently available. Consequently, the development of microbial strategies for disease management has become increasingly important. Among these, plant immunity-intensifying microbes have demonstrated promising efficacy in controlling bacterial wilt. However, the influence of environmental factors, particularly light intensity, on the effectiveness of these microbes remains unclear. Light intensity is a critical regulator of the photosynthetic system and plant biochemical functions, including defense responses. In this study, we specifically utilized Arabidopsis plants grown under distinct light intensities to systematically examine how light conditions affect the induction of plant immune responses and the occurrence of bacterial wilt. Our findings revealed that Arabidopsis grown under high light intensity exhibited significantly stronger immune responses and reduced disease severity, compared to plants grown under low light intensity. Further, application of Bacillus amyloliquefaciens PMB05, a plant immunity-intensifying strain, resulted in more pronounced immune signaling and disease control efficacy under high light conditions. Experiments using salicylic acid (SA)-deficient mutants demonstrated that disruption of the SA pathway abolished the enhanced suppression of bacterial wilt conferred by B. amyloliquefaciens PMB05 under high light intensity, indicating that the SA pathway is indispensable for PMB05-mediated disease resistance. Moreover, the validation experiments in tomato plants supported these results, with B. amyloliquefaciens PMB05 significantly reducing bacterial wilt development under high light intensity. Collectively, our study demonstrates that growing plants under varying light intensities provides critical insights into how environmental conditions modulate the effectiveness of plant immunity-intensifying microbes, offering a potential strategy for integrated disease management in crops.