Characterization of plant growth promoting rhizobacteria and their potential as bioprotectant against tomato bacterial wilt caused by Ralstonia solanacearum

•Out of 150 only 13 isolates inhibited Ralstonia solanacearum in vitro condition.•Thirteen isolates identified as Pseudomonas spp. and Bacillus spp. Serratia marcescens.•Of 13 isolates 11 produced siderophore, nine solubilized phosphate and all produced indole acetic acid (IAA).•In ad planta Bacillus cereus and Pseudomonas putida reduced bacterial wilt in tomato genotypes. Bacterial wilt caused by Ralstonia solanacearum is one of the most destructive bacterial diseases of tomato and other economically important crops. To develop a biological control strategy against the pathogen, 150 isolates of rhizobacteria were isolated and screened for in vitro antibiosis. Thirteen isolates inhibited the growth of R. solanacearum and were identified with Fatty Acid Methyl Ester (GC-FAME) and biochemical methods asPseudomonas spp.,Serratia marcescens and Bacillus cereus. These isolates were further characterized for their plant growth promoting traits and production of the quorum sensing signal molecule acyl-homoserine lactones (AHL). Based on the in vitro antibiosis, four isolates, viz. B. cereus BC1AW, BC2BA, BC3AW, BC4SS and Pseudomonas putida PP3WT were selected for ad planta tests. Isolates BC1AW and PP3WT significantly reduced bacterial wilt incidence in tomato genotypes King Kong 2 (moderately resistant) in the pot experiments by 46.8% and 44.7% and in L390 (susceptible) by 33.6% and 30%, respectively. While in split root experiments they reduced wilt incidence by 48.7%, 43.2% and 25.7% and 20.1% in King Kong 2 and L390, respectively. Shoot dry weight also increased in plants treated with BC1AW and PP3WT and reduced the number of R. solanacearum cells by in mid-stems of both tomato genotypes. Hence, BC1AW and PP3WT were selected as promising biocontrol isolates whose effectiveness under field conditions and mode of action at molecular level should be investigated.