Identification, characterization and genetic diversity of Ralstonia pseudosolanacearum causing bacterial wilt of tomato in Himachal Pradesh, India

Ralstonia solanacearum species complex (RSSC) is a group of highly destructive phytopathogens known for their significant genetic and phenotypic variability. Strains of this complex affect a wide range of crops, as well as ornamentals and weeds. In the present study, bacterial wilt-infected tomato plants were collected from 42 tomato growing villages of Mandi, Kullu, Solan and Kangra districts of Himachal Pradesh, India during summer of 2024. A total of 158 isolates were identified by the RSSC-specific primer pair 759/760. Using the biovar classification scheme, 111 isolates (70.25 %) were classified as biovar 4 and 47 (29.75 %) as biovar 3. Further, phylotype-specific multiplex PCR assigned all 158 isolates to phylotype I identifying them as R. pseudosolanacearum. Morphological analysis of a representative strain (HToR31) using transmission electron microscopy revealed rod-shaped cells measuring 0.55–0.65 μm in diameter and 1.30–1.80 μm in length, with a polar flagellum. Furthermore, partial egl gene sequencing of 27 randomly selected strains from the four districts revealed the presence of six sequevars: I-44, I-46, I-47, I-57, I-70, and I-71. Notably, all sequevars except I-47 were reported for the first time in India. This study provides valuable insights into the genetic and biovar diversity of RSSC strains in Himachal Pradesh, India.