Plant growth-promotion (PGP) activities and molecular characterization of rhizobacterial strains isolated from soybean (Glycine max L. Merril) plants against charcoal rot pathogen, Macrophomina phaseolina.

Charcoal rot disease, caused by the fungus Macrophomina phaseolina, leads to significant yield losses of soybean crops. One strategy to control charcoal rot is the use of antagonistic, root-colonizing bacteria. Rhizobacteria A(5)F and FPT(7)21 and Pseudomonas sp. strain GRP(3) were characterized for their plant growth-promotion activities against the pathogen. Rhizobacterium FPT(7)21 exhibited higher antagonistic activity against the pathogen on dual plate assay compared to strain A(5)F and GRP(3). FPT(7)21 and GRP(3) gave decreased disease intensity in terms of average number of pathogen-infested plants. Lipoxygenase (LOX), phenylalanine ammonia-lyase (PAL), and peroxidase (POD) activities were estimated in extracts of plants grown from seeds that were treated with rhizobacteria, and inoculated with spore suspension of M. phaseolina. The activity of these enzymes after challenge with the test pathogen increased. Strains FPT(7)21 and GRP(3) exhibited maximum increases in LOX, PAL and POD activity (U mg(-1) fresh leaf wt) compared to strain A(5)F.