Genetic diversity of Indian isolates of Ralstonia solanacearum causing bacterial wilt of eggplant (Solanum melongena)

Thirty-eight isolates of Ralstonia solanacearum were isolated from wilted eggplants from seven states of India, i.e. Uttarakhand, Himachal Pradesh, Jharkhand, Odisha, West Bengal, Karnataka and Meghalaya on TTC medium to study their genetic diversity using BOX, ERIC and REP-PCR's. All isolates of R. solanacearum produced fluidal, irregular pinkish-white colonies and they belonged to biovar 3, race 1 and phylotype I. The study also included five out-group bacteria (Bacillus subtilis DTBS-5, Pseudomonas fluorescence DTPF-3, Xanthomonas campestris pv. campestris Xcc-C4, X. citri subsp. citri Xac-C63 and X. oryzae pv. oryzae Xoo-4). The isolates of R. solanacearum and out group bacteria were grouped into10 DNA types at 75% similarity coefficient. Maximum 11 isolates of R. solanacearum isolated from West Bengal were grouped into DNA Type 2. The isolates collected from Uttarakhand grouped into DNA types 6, 7, 8 and 10. However, all out-group bacteria were clearly separated from the isolates of R. solanacearum as DNA type 9. Multilocus sequence analysis of 18 isolates of R. solanacearum along with sequences obtained from NCBI database of 2 out-group bacteria (Burkholderia multivoransATCC-17616 and X. campestris pv. campestris ATCC-33913) was done using sequences of hrpB (hypersensitive response gene), fliC (flagelline protein) and egl (endoglucanase gene). Sequence comparisons showed high level of variability within these three regions of the genome involved in pathogenicity. On the basis of phylogenetic analysis, the selective pressure on virulence-related genes of R. solanacearum was identified. This genetic diversity presents major challenges for developing effective long-term management strategies to control the wilt disease of eggplant.