Curtobacterium flaccumfaciens pv. flaccumfaciens (Cff) is a seed-borne pathogenic bacterium that causes tan spot of mung bean (Vigna radiata) and several members of the Fabaceae. Tan spot is a widespread but sporadic disease of mung bean, capable of impacting yield under conducive conditions. The pathogenicity and genetic diversity of Australian Cff isolates have recently been examined, describing a linear plasmid as a pathogenicity factor. Six genetic clusters were reported among 117 Australian Cff isolates, with most of the variation in the collection attributed to clonal expansion. Genetically diverse isolates were identified from single leaves, and a subsequent study was performed to examine the competitive interactions among a group of diverse isolates. Initially, four isolate-specific PCR assays were designed to allow quantification of each isolate in mixed samples. Three pathogenic isolates were inoculated into broth and mung bean plants in 17 combinations (including mixtures and pure inoculum), and two isolates, representing pathogenic and non-pathogenic types, were similarly inoculated as six combinations. Quantities of each isolate were determined for inoculum, broth and mung bean samples using isolate-specific assays in droplet digital PCR. Competition and/or inhibition among isolates was observed, with some responses contrasted between broth and mung bean treatments. Disease severity and total bacterial loads were similar for pure and mixed inoculum treatments on mung bean. Growth inhibition (and disease suppression) of a pathogenic isolate was also observed when in combination with the plasmid-less non-pathogenic isolate in both broth and mung bean tissues. Intra-species inhibitory effects of Cff have previously been described in vitro and potentially linked to bacteriocin production. Research is on-going to determine what chemicals are produced by Australian Cff isolates and how these may be harnessed for crop protection.