Biological Control of Bacterial Wilt of Tomato by Plant Growth Promoting Rhizobacteria

Seven isolates of Ralstonia solanacearum were isolated from naturally wilted roots of tomato plants grown in Assiut governorate. All isolates were pathogenic to tomato plants and produced typical symptoms of wilt. Isolate No. 5 exhibited the highest virulence followed by isolate No. 4. Pseudomonas fluorescens, P. putida, Bacillus subtilis and Enterobacter aerogenes were isolated from tomato rhizosphere and tested against R. solanacearum in vitro and in vivo. Results showed that all PGPR strains except E. aerogenes, increased seed germination up to 15% over untreated control. Under greenhouse conditions, P. fluorescens exhibited the highest disease reduction of tomato bacterial wilt disease followed by P. putida and then B. subtilis while E. aerogenes showed the lowest disease reduction percentage. Also tomato plants treated with all PGPR isolates significantly stimulated plant growth promotion under greenhouse conditions. In field trails, addition of P. fluorescens, P. putida and B. subtilis at concentration of 108 cfu mL-1 showed that Pseudomonas fluorescens caused the highest disease reduction percentage of tomato bacterial wilt disease while P. putida exhibited the lowest disease reduction percentage.