Phylotype, sequevar and pathogenicity of Ralstonia solanaceaum species complex from Northern Thailand

Abstract

Ralstonia solanacearum species complex is a group of vascular soil-borne plant pathogens that causes bacterial wilt on various host plants and has caused great yield losses in Thailand. In 2020 and 2021, bacterial wilt diseases were observed in Chiang Mai and Chiang Rai Province, Thailand. Approximately 19 bacterial wilt strains that were infecting 10 plant species were identified. The different bacterial wilt strains were characterized based on biovar test, phylotypes and DNA sequence of egl gene to determine their sequevar classification. The results of biovar tests by oxidation of disaccharides and hexose alcohols showed the strains belong to biovars 2T, 3 and 4. The partial egl gene sequence analysis of the strains clustered into five type groups that included phylotype IIA sequevar 1 as R. solanacearum and phylotype I, which included 4 sequevars (13, 17, 30 and 47) as R. pseudosolanacearum. The results showed that tomato, Thai eggplant and marigold were susceptible to all bacterial wilt strains. Furthermore, R. pseudosolanacearum biovar 2T phylotype I sequevar 17 was specifically pathogenic to pumpkin and cucumber, but sequevar 13 produced bacterial wilt symptoms on cucumber, and the two sequevars were non-symptomatic on Patumma and turmeric. R. pseudosolanacearum biovar 4 phylotype I sequevar 30 was specifically pathogenic to Patumma and turmeric. This new report expands the knowledge on genetic analysis and host range diversity of the R. solanacearum species complex in Thailand.