Occurrence and characterization of a new red-pigmented variant of Curtobacterium flaccumfaciens, the causal agent of bacterial wilt of edible dry beans in Iran.
A number of crop diseases are emerging at an alarming rate worldwide. Bacterial wilt of dry beans, caused by Curtobacterium flaccumfaciens pv. flaccumfaciens (Cff), is one of them. In Iran, this disease was first reported in 2012, which, since then, has rapidly spread across the major dry bean growing areas of the country causing severe yield losses. Previously, only two colony variants (yellow and orange) of the pathogen had been described from Iran in association with bacterial wilt of dry beans. In this study, we describe a new red-pigmented variant of Cff, isolated from dry bean seeds stored in seed banks of Khomein Bean Research Station, the major seed supplier in the region. Because Cff is a quarantine pathogen in Iran and elsewhere, with a potential threat for dry bean productions, more knowledge about the biology of this pathogen and epidemiology of the disease it causes are a prerequisite for the development of effective disease management strategies. Within this framework, we performed phenotypic and genetic characterization of the red-pigmented variant of the pathogen, in comparison with previously isolated yellow and orange variants, including pathogenicity, host range, bacteriocin production and genetic diversity. Our results showed a similar host range of different Cff variants although they differed in their aggressiveness. Yellow and orange variants of the pathogen were more aggressive on cowpea and common bean, respectively while the red variant showed the same level of aggressiveness on both hosts. Orange- and red-pigmented strains were separated from yellow-pigmented strains in the phylogeny of gyrB sequences. All orange- or red-pigmented strains were clustered in a separate branch from yellow-pigmented strains, except strain CffK31, in phylogeny based on rpoB sequences. In BOX-PCR analysis, Cff strains used in this study were clustered in two distinct genetic groups, with yellow variants of the pathogen separated from the orange and red variants. Overall, our results provide evidence of a remarkable diversity of Cff in Iran, which needs further in-depth investigation.