ABSTRACT No information regarding pathogenic variability among different isolates of Ralstonia solanacearum infecting chili from different agro-ecological zones of Pakistan with varying climatic and edaphic factors is available. Therefore, in the present study, variations were observed in biovar distribution, hypersensitive response, growth and virulence among 114 isolates of R. solanacearum collected from eight agro-ecological zones of Pakistan. Out of 114 R. solanacearum isolates, 81% were identified as Biovar III, while the remaining 19% were recognized as Biovar IV. Of all the 114 isolates of R. solanacearum, 77% showed positive hypersensitive response and mucoid growth, while 23% isolates gave negative hypersensitive response with non-mucoid growth. Out of 114 isolates of R. solanacearum consisting of Biovar III and IV, 22.8% were found avirulent, 25.4% weakly virulent, 29.8% virulent, and the remaining 21.9% were highly virulent. Variations among 114 R. solanacearum isolates were also observed in four provinces of the country. Among 92 R. solanacearum Biovar III isolates, 21.7% were identified as avirulent, 25% weakly virulent, 34.4% virulent, and 22.8% were highly virulent in the eight agro-ecological zones of the country. Similarly, out of 22 R. solanacearum Biovar IV isolates, 27.3% were detected as avirulent, weakly virulent and virulent, while 18.2% isolates were found highly virulent. The isolates having non-mucoid growth and negative hypersensitive response were found avriulent, while those with mucoid growth and positive hypersensitive response were weakly virulent to highly virulent. The information will help design control strategies accordingly and develop resistant cultivars against the bacterium.

ABSTRACT The production of chili is seriously threatened by bacterial wilt incited by Ralstonia solanacearum in Pakistan. As the information about the distribution and prevalence of the disease and the pathogen is scarce, the present study was performed to ascertain the prevalence, occurrence and distribution of R. solanacearum in different regions of chili cultivation. The results showed differences in the incidence and prevalence of bacterial wilt all over the country. Overall, an incidence of 10% and prevalence of 76% of the disease was observed in the country. The highest incidence of bacterial wilt was observed in the province of Sindh whereas it was the lowest in Baluchistan. The prevalence of the disease followed the similar trend in the provinces. As regards agroecological zones, the highest incidence was recorded in Indus delta followed by sandy deserts whereas it was the lowest in western dry mountains. Almost the same tendency was observed regarding prevalence in the eight agroecological zones. In case of districts, the disease incidence was the maximum in Badin while it was the minimum in the district of Loralai. On the other hand, the disease prevalence was the maximum (100%) in the districts of Badin, Mirpurkhas, and Thatta and the minimum (60%) in the districts of Barkhan, Karak, and Loralai. Of the total 114 isolates of R. solanacearum, 81% were confirmed as Biovar 3 whereas the rest 19% isolates were identified as Biovar 4. The findings will help the farmers to design disease management programs accordingly to avert yield losses.

ABSTRACT 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 °C, while none of the isolates produced its colony at 41 °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.