Diversity of cultivable rhizobacteria across tomato growing regions of Karnataka

Seven hundred and fifty-two rhizobacteria were isolated from 186 rhizosphere soil samples collected
across tomato growing regions of Karnataka. Among them, 26% strains were Gram positive and other
74% were Gram negative and dominant being Bacillus and Pseudomonas. Sampling of different locations
showed variation in species richness and diversity indices. Similarity matrix computed with Jaccard’s
coefficient and principle coordinate analysis to correlate bacterial diversity revealed that rhizobacterial
genera of Mysore, Mandya and Kolar soil samples were very closely related and rarefaction curve analysis
indicated that these soil samples also harbored higher number of rhizobacteria which included all the
genera studied. PGPR trait analysis revealed that most of the rhizobacteria were endowed with more than
one beneficial trait which may act individually or simultaneously, and indole acetic acid production and
phosphate solubilization are the two predominant traits exhibited by these rhizobacteria. Rhizobacterial
isolates also showed a varied level of plant growth promotion traits and offered protection against fungal
origin foliar and root pathogens. Among the nine regions studied, Mysore, Mandya and Kolar regions
recorded higher percentage of promising PGPRs in comparison with other regions studied of Karnataka.