Epiphytic Curtobacterium flaccumfaciens strains isolated from asymptomatic solanaceous vegetables are pathogenic on leguminous but not on solanaceous plants

During 2013-2016, sixteen Gram-positive Corynebacterium-like strains were recovered from the epiphytic parts of solanaceous vegetables including eggplant, pepper and tomato, in Iran. The strains were recovered accidentally as a result of monitoring for other bacterial pathogens in solanaceous fields. The strains were phenotypically different from Clavibacter michiganensis strains. Although none of the strains were pathogenic on their host of isolation or on any other solanaceous plants, 12 out of 16 strains were pathogenic on common bean, cowpea, mung bean, and soybean. Colonization by strains was observed on corn, zucchini, faba bean, honeydew, rapeseed, sugar beet, and sunflower plants under greenhouse conditions. In PCR tests, the primer pair CffFOR2/CffREV4, specific for Curtobacterium flaccumfaciens pv. flaccumfaciens, directed the amplification of the appropriately sized fragment in 12 out of 16 strains, and all 12 strains were pathogenic on dry beans. Phylogenetic analysis, using the gyrB and recA genes, showed all 16 bacterial strains clustered within several pathovars of C. flaccumfaciens. A non-pathogenic yellow-pigmented strain (Xeu15) was clustered with the type strains of C. flaccumfaciens pv. betae and C. flaccumfaciens pv. oortii. Bacteriocin profiling assays revealed no significant differences among the pathogenic and non-pathogenic strains. Host range and population dynamics of four representative strains on seventeen plant species showed population build-up of the strains only on common bean, cowpea, and red nightshade plants. Taken together, our results provide important insights into the possible role of non-host plants as reservoirs of plant pathogenic bacteria, which has important implications in plant disease epidemiology and management.