Utilization of plant growth promoting Bacillus subtilis isolates for the management of bacterial wilt incidence in tomato caused by Ralstonia solanacearum race 1 biovar 3

Abstract

Bacterial wilt of tomato caused by Ralstonia solanacearum race 1 biovar 3 is one of the most economically important diseases of tomato in India. Bacillus subtilis isolates were isolated from rhizospheric soil of wilt infected tomato plants from different agro-climatic regions of India. These isolates were evaluated for their antagonistic ability to reduce incidence of bacterial wilt of tomato and plant growth promoting attributes. Twenty-four and 48 h old cultures of B. subtilis BS-5 inhibited growth of R. solanacearum by forming area of inhibition zone 4.90 cm2 and 5.87cm2 respectively under in vitro conditions. No significant difference in reduction of bacterial wilt incidence in tomato was observed among BS-5, BS-1 and BS-4 isolates of B. subtilis (P= < 0.0001) under glasshouse conditions. However, minimum disease incidence (9.27%) was observed in BS-5 treated soil, which has significantly performed better than untreated control after 35 days of inoculation with Ralstonia solanacearum and B. subtilis. Among the nine isolates of B. subtilis tested for plant growth promoting attributes, BS-9 exhibited maximum phosphorus solubilization (64μg/ml), siderophore production (1.20 cm diameter), indole acetic acid production (0.139 μg/ml) and ammonia production in vitro, while under glasshouse condition, it increased height of tomato plants and biomass production, which was better than untreated control. The isolates, those having both antagonistic and plant growth promoting ability were confirmed to be B. subtilis by using specific 16S rRNA based marker. The isolates of B. subtilis isolated from rhizospheric soil of tomato possessed antagonistic and PGP attributes, preferred to grow under acidic conditions. Further, field studies should be undertaken to evaluate the performance of these isolates under natural environment before going for preparation of formulation.