The sequevar distribution of Ralstonia solanacearum in tobacco-growing zones of China is structured by elevation

Abstract

Bacterial wilt, caused by Ralstonia solanacearum, is a devastating disease resulting in tremendous losses of economic crops such as plants in the Solanaceae. Recent studies showed that R. solanacearum is spreading from the lowlands to the highlands in China. We studied 97 Chinese R. solanacearum strains that were isolated from four tobacco-growing zones over a wide range of elevations using phylotype specific multiplex polymerase chain reaction (Pmx-PCR) and phylogenetic relationships (egl and mutS). The results showed that all isolates belonged to phylotype I, which were further clustered into eight egl-sequence type groups (egl-group, sequevar): sequevars 13, 14, 15, 17, 34, 44, 54, and 55. In addition, Sequevar 55, found from the highlands, was a new/unknown one. Southeast China (Z3) had the largest number of egl-groups, containing six sequevars. The basin of the Yangzi River (Z1) and southwestern China (Z2) contained five egl-groups. The basin of the Huai River (Z4), near the north of China, where slight bacterial wilt occurred recently, contained a single group, sequevar 15. The distribution of sequevars was associated with elevation. Sequevar 15 was over-represented in lowland elevations, while sequevar 54 and the new/unknown one were only found in areas of moderate to high elevations. This finding suggested that the phylotype I strains infecting tobacco were diverse in China and regional integrated control strategies should be considered.