Characterization of Ralstonia solanacearum causing bacterial wilt from chili areas of Pakistan

For proper disease management, accurate diagnosis of the pathogen is essential. Therefore, in the present study Ralstonia solanacearum causing bacterial wilt of chili was characterized to determine the distribution of biovars of the bacterium in the eight agroecological zones with varying climatic conditions and edaphic factors. Among all the 114 isolates of R. solanacearum, 77% showed mucoid growth while 23% isolates gave non-mucoid growth. Similarly, the isolates with mucoid growth were found positive for hypersensitivity response (HR), while those with non-mucoid growth showed negative HR. All the isolates grew well at 37 degrees C, while none of the isolates produced its colony at 41 degrees C. All the 114 isolates of R. solanacearum showed positive responses for all the biochemical tests used for confirmation of the bacterium. Out of 114 R. solanacearum isolates, 81% were identified as Biovar III while the remaining 19% were recognized as Biovar IV. Biovar III constituted 37 and 70% in the provinces of Punjab and Sindh, respectively, while Biovar IV formed 19 and 30%. On the other hand, in Khyber Pakhtunkhwa and Balochistan, only Biovar III was recorded. Similarly, Biovar III was observed from all the eight agroecological zones of the four provinces of the country and found to be predominant. On the other hand, Biovar IV was recorded from four agroecological zones located in the provinces of Punjab and Sindh. All the isolates yielded a 750-bp band that corresponded to R. solanacearum. It is concluded that Biovar III is widely prevalent in the country warranting stringent control measures.