Effect of temperature, cultivars, injury of root and inoculums load of Ralstonia solanacearum to cause bacterial wilt of tomato

Abstract

Bacterial wilt, caused by Ralstonia solanacearum , is responsible for severe losses in tomato crops in the world. In the present study, the effect of temperature, cultivars of tomato, injury of root system and inoculums load of R. solanacearum to cause bacterial wilt disease under control conditions was undertaken. Three strains UTT-25, HPT-3 and JHT-5 of R. solanacearum were grown at 5–40 °C in vitro to study, the effect of temperature on the growth of bacteria and maximum growth was found at 30 °C after 72 h in all the strains. Twenty-one days old seedlings of two cultivars of tomato i.e. N-5 (moderately resistant) and Pusa Ruby (highly susceptible) were transplanted into the pots and inoculated with R. solanacearum strain UTT-25 (5 × 108 cfu/ml), mechanically injured and uninjured roots of the plant. The plants were allowed to grow at 20, 25, 30 and 35 °C at National Phytotron Facility, IARI, New Delhi to study the effect of temperature on intensity of bacterial wilt disease. Maximum wilt disease intensity was found 98.73 and 95.9 % in injured roots of Pusa Ruby and N-5 cultivars of tomato at 35 °C on 11th days of inoculation, respectively. However, no wilt disease was observed in both the cultivars at 20 °C up to 60 days. For detection of R. solanacearum from asymptomatic tomato plants, hrpB-based sequence primers (Hrp_rs2F and Hrp_rs2R) amplified at 323 bp was used in bio-PCR to detect R. solanacearum from crown, mid part of stem and upper parts of the plant. Another experiment was conducted to find out the inoculum potential of R. solanacearum strain UTT-25 to cause bacterial wilt in susceptible cultivar Pusa Ruby. The bacteria were inoculated at concentration of bacterial suspension 10 to 1010 cfu/ml in injured and uninjured roots of the plants separately and injured root accelerated wilt incidence and able to cause wilt disease 63.3% by 100 cfu/ml of R. solanacearum, while no disease appeared at 10 cfu/ml on the 11th day of inoculation in injured and uninjured roots of the plant.