Characterization of Ralstonia solanacearum species complex strains causing bacterial wilt of tomato in Louisiana, USA

A baseline for genetic diversity of Ralstonia solanacearum species complex (RSSC) causing bacterial wilt of field and greenhouse grown Solanum lycopersicum (tomato) in Louisiana was established based on biovar, phylotype and phylogenetic analysis of the egl gene sequence. RSCC strains were characterized as Biovars 1, 3 and 6 and belonged to phylotypes I and II. Phylotypes were subdivided into sequevars based on differences in the nucleotide sequence of the egl gene. Phylotype II strains clustered with closely related North American strains in sequevar 7 and phylotype I strains clustered with Asian strains in sequevar 14. All three RSCC strains isolated from greenhouse grown tomato were phylotype II sequevar 7 and were identical to strain AW1 from tomato in Alabama (AL). While all RSCC strains were pathogenic on tomato ‘Roma’, only six induced a hypersensitive reponse (HR) on Nicotiana tabacum. Four of the HR positive strains were also pathogenic on pepper ‘Yolo Wonder’. This is the first study to characterize RSSC strains causing bacterial wilt of tomato in Louisiana and confirms that strains originating from Asia are present in North America. Genetic characterization of RSCC strains currently present in Louisiana is the first step towards the development of strain-specific management practices, including the identification of strain-specific host resistance.