Genetic diversity of Ralstonia solanacearum and disease management strategy

Abstract

Ralstonia solanacearum (Smith) (Yabuuchi et al. 1996) is the causal organism of bacterial wilt of more than 200 species representing 50 families of plants, including economically important crops such as potato, tomato, eggplant, and banana. Bacterial wilt is one of the most important diseases causing a major constraint on farmers. The disease has been widely recognized in tropical, subtropical and warm temperate regions of the world (Hayward 1991, 1994a). Isolates of R. solanacearum differ in host range, geographical distribution, pathogenicity, epidemiological characters, and physiological properties. To describe this intraspecific variability of R. solanacearum, researchers have devised many classification schemes to identify this bacterium and understand its evolution (Horita and Tsuchiya 2009). For more than 5 decades, R. solanacearum has been mainly classified according to race and biovar, based on differences in host range and biochemical properties, respectively (Denny and Hayward 2001; Hayward 1964, 1994b). Consequently, over the last 3 decades, molecular biological studies have been introduced to classify and identify R. solanacearum strains from diverse origins. In various genetic analyses, genetic variability between and within the population of R. solanacearum has been assessed. On the basis of results obtained by molecular analyses, R. solanacearum has become defined as a species complex (Gillings and Fahy 1994; Poussier et al. 2000b; Villa et al. 2005), and a new classification system has been suggested (Fegan and Prior 2005; Remenant et al. 2011). In this paper, I discuss three topics: (1) current classification schemes of R. solanacearum, (2) the genetic diversity of the pathogenic strains, in particular, those of potato and Zingiberaceae plants in relation to continuously present or newly emergent diseases in Japan, and (3) perspectives on disease control strategies.