P-673 - Competitive dynamics among Curtobacterium flaccumfaciens isolates

Curtobacterium flaccumfaciens pv. flaccumfaciens (Cff) causes tan spot of mung bean (Vigna radiata) in Australia and also affects a range of Fabaceae worldwide. A linear plasmid has been reported as a pathogenicity factor. Genetic diversity was recently reported from an Australian isolate collection, with genetically distinct isolates observed within single leaves. This study examined intra-species competition among genetically diverse Cff isolates to assess growth dynamics and disease responses. Isolate-specific PCR assays were designed to quantify four individual isolates in mixed samples using droplet digital PCR. Three pathogenic isolates were inoculated into broth and mung bean plants across 17 combinations, while two isolates representing pathogenic and non-pathogenic (plasmid-free) types were tested in six combinations. Isolate quantities were measured across inoculum, broth, and plant samples. Competitive interactions among isolates were observed, with variations between broth and plant treatments. Disease severity and total bacterial loads remained similar across pure and mixed inoculum treatments. Notably, co-inoculation with the non-pathogenic isolate led to suppressed growth of a pathogenic isolate, along with reduced disease expression in mung bean, suggesting potential inhibitory mechanisms. Intra-species inhibition in Cff has been linked to bacteriocin production, which could offer novel avenues for disease management. Future research aims to identify bioactive compounds from Australian Cff isolates and explore their potential applications in crop protection.