Evaluation of colonization efficiency and migration pathways of <i>Bacillus amyloliquefaciens</i> GZY63 in <i>Camellia oleifera</i>

Bacillus spp. can colonize various plant tissues, promoting growth and providing biocontrol. Bacillus amyloliquefaciens GZY63 exhibits strong antagonistic activity against anthracnose pathogens in Camellia oleifera. However, its potential as a biocontrol agent in Ca. oleifera remains underexplored, mainly because knowledge regarding its colonization behavior in this host plant is limited. In this study, we used a chloramphenicol-resistant GFP-tagged GZY63 strain to assess the colonization patterns of the bacterium in Ca. oleifera through quantitative Polymerase Chain Reaction (qPCR). In particular, we investigated the bacterium's colonization dynamics across three Ca. oleifera varieties, with a focusing on differences between the root and foliar inoculation methods. The results revealed that root inoculation of B. amyloliquefaciens GZY63 resulted in significantly higher colonization efficiency and more rapid bacterial translocation to leaf tissues than its foliar inoculation. Moreover, the colonization efficiency varied among the three Ca. oleifera varieties, indicating that host genotype influences the bacterium's endophytic compatibility. Although the underlying biochemical factors and regulatory mechanisms remain unclear, our results provide valuable insights into host-microbe interactions in Ca. oleifera. These findings provide a theoretical basis for optimizing the application of B. amyloliquefaciens GZY63 as biocontrol agent in Ca. oleifera and underscore the importance of selecting compatible host genotypes for effective microbial inoculation.