Development and Utilization of Quantitative Detection for Probiotics Bacillus velezensis B31 with Potential Protection Against Tomato Fusarium Wilt

The biocontrol efficacy of probiotics Bacillus velezensis B31 against fusarium wilt is contingent upon its successful colonization in the plant rhizosphere. This study aimed to develop a quantitative detection method for probiotics strain B31 and to monitor its rhizosphere dynamics. Utilizing comparative genomics, a specific gene in strain B31 was identified, which facilitated the design of precise primers and a Taqman probe. The resulting real-time PCR assay demonstrated high specificity to strain B31 and high sensitivity with detection limit of 28 copies/µL of the genome. Comparative analysis with regular PCR methods revealed a strong correlation, yet highlighted the superior sensitivity and rapidity of the real-time PCR technique. The temporal colonization profile of strain B31, post root-inoculation, was charted using this assay. An initial rhizosphere population of 7.2 × 10 7 CFU g^-1 was observed, which then tapered to 10 5 CFU g^-1 over 14 days. These dynamics corresponded with the observed control effect, where a higher initial population correlated with enhanced disease suppression. This study underscores the potential of real-time PCR as a robust tool for biocontrol agents' monitoring, offering insights into the microbial interactions within the rhizosphere.