Phylotype and sequevar variability of Ralstonia solanacearum in Brazil, an ancient centre of diversity of the pathogen

Abstract

The β‐proteobacterium Ralstonia solanacearum causes bacterial wilt of many plant species. Knowledge of phylotype and sequevar variability in populations of this microorganism is useful for implementing control measures, particularly host resistance. To this end, 301 isolates of R. solanacearum were collected from different geographic regions and hosts in Brazil. Their phylotype and sequevar characterization was used to determine the amount and distribution of phenetic and phylogenetic variability. Isolates were classified into phylotypes I (n = 48), clade 1; and phylotype II, clades 2–5. Phylotype II was divided into subclusters IIA (n = 112) and IIB (n = 141). Phylotype II was widely distributed, whereas phylotype I isolates were found in Central, Northern, and Northeastern regions of Brazil. There were 108 haplotypes identified among endoglucanase (egl) gene sequences from 301 isolates and 32 haplotypes among DNA repair (mutS) gene regions from 176 isolates. The egl and mutS sequence analyses identified eight known (1, 4, 7, 18, 27, 28, 41 and 50) and four new (54, 55, 56 and 57) sequevars. Phylotype IIB showed high diversity in sequevars and host range. Multiplex PCR, using primers specific to the Moko ecotype, characterized banana and long pepper isolates as sequevar 4 and 4/NPB, respectively. This constitutes the first report of the emergent ecotype IIB/4NPB in a new host, long pepper. The majority of sequevars were associated with geographic regions. This high variability of R. solanacearum in Brazil suggests use of host resistance to control bacterial wilt should be mainly focused by region.