Fifty seven rhizobacteria were isolated from rhizospheric soil of wilted tomato plants and among them two strains of rhizobacteria, having better antagonistic and plant growth promoting ability were characterized them as Bacillus amyloliquefaciens DSBA-11 and DSBA-12 based on morphological, biochemical, partial gene sequence analysis of 16S rRNA and fatty acid methyl ester analysis. Antagonistic activity of these strains DSBA-11, DSBA-12 was compared with other Bacillus species such as B. subtilis DTBS-5, B. cereus JHTBS-7, B. pumilus MTCC-7092 strains, against Ralstonia solanacearum race 1, bv 3, phylotype I, inciting bacterial wilt of tomato underin vitro conditions. B. amyloliquefaciens DSBA-11 showed maximum growth inhibition of R. solanacearum (4.91cm 2 ) followed by strains DSBA-12 (3.31cm 2 ) and B. subtilis (3.07 cm 2 ). Moreover, strains DSBA-11 was also have better phosphorus solubilizing ability (42.6 µg/ml) and indole acetic acid (95.4 µg/ml) production than other strains of Bacillus spp. in vitro conditions. Biocontrol efficacy and plant growth ability of these bacterial antagonists was tested against bacterial wilt of tomato cv. Pusa Ruby under glasshouse conditions. Minimum bacterial wilt disease incidenceincultivar Pusa Ruby (17.95%) was recorded in B. amyloliquefaciens DSBA-11followed by B. amyloliquefaciens DSBA-12 after 30 days of inoculation.The bio-control efficacy was higher in B. amyloliquefaciens DSBA -12 treated plants, followed by B. pumilus MTCC-7092.

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Bacterial wilt of tomato caused by Ralstonia solanacearum (Smith) Yabuuchi et al. (Microbiol Immunol 39:897-904, 1995) is a serious disease, which causes losses up to 60 % depending on environmental conditions, soil property, and cultivars. In present investigation, nucleotide sequences of virulence, hypersensitive response and pathogenicity (hrp) gene were used to design a pair of primer (Hrp_rs 2F: 5'-AGAGGTCGACGCGATACAGT-3' and Hrp_rs 2R: 5'-CATGAGCAAGGACGAAGTCA-3') for amplification of bacterial genome. The genomic DNA of 27 isolates of R. solanacearum race 1 biovar 3 & 4 was amplified at 323 bp. The specificity of primer was tested on 13 strains of R. solanacearum with other group of bacteria such as Xanthomonas oryzae pv. oryzae, X. campestris pv. campestris, and X. citri subsp. citri. Primer amplified DNA fragment of R. solanacearum at 323 bp. The sensitivity of the primer was 200 cfu/ml and improved further detection level by using non-specific enrichment medium casamino acids-pepton-glucose broth followed by PCR (BIO-PCR). Out of 130 samples of asymptomatic tomato plants, irrigation water, and soil collected from bacterial wilt infested field in different agro-climatic regions of India, R. solanacearum was detected from 86.9, 88.5, and 90.9 per cents samples using BIO-PCR, respectively. The primer was found specific for detecting viable and virulent strains of R. solanacearum and useful for the diagnosis of R. solanacearum in tomato seedlings and monitoring of pathogen in irrigation water and soil.

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