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How Andean Ralstonia solanacearum potato brown rot strains displace African brown rot strains in the Madagascar highlands

Alicia Truchon: University of Wisconsin

<div><em>Ralstonia solanacearum</em> (<em>Rs</em>) causes potato brown rot (BR), a serious problem in tropical highlands worldwide. A 2009 survey in Madagascar revealed a widespread BR outbreak. Malagasy potato growers depend on this crop for sustainable food security. Epidemiological and phylogenetic analyses suggested that the recently introduced Andean phylotype II, sequevar 1 (Race 3 biovar 2) <em>Rs</em> strains spread quickly, displacing native African (Phylotype III) <em>Rs</em> strains. Andean strains are highly destructive because they disperse rapidly in potato seed tubers, but there is no published information on transmission of African BR strains. Understanding pathogen transmission is essential for effective disease management. Based on epidemiological data, we hypothesize that African BR strains may not be efficiently tuber transmitted. Using 11 diverse African BR isolates from Madagascar (phylotype III, sequevars 19 and 60) and the well characterized Andean Race 3 biovar 2 strain UW551, we performed comparative bioinformatic and biological analyses to identify differences between Andean and African <em>Rs</em> strains that infect potato. We sequenced genomes from one sequevar 19 and one sequevar 60 African strain, and compared their virulence on potato and tomato, as well as their tuber colonization and tuber transmission on potato. Biological differences between Andean and African BR strains may explain the displacement of African <em>Rs</em> strains by Andean strains in the Madagascar highlands.</div>