Induction of pathogenesis-related proteins during biocontrol of Rhizoctonia solani with Pseudomonas aureofaciens in soybean (Glycine max L. Merr.) plants

To investigate the biocontrol effectiveness of the antibiotic producing bacterium, Pseudomonas aureofaciens 63-28 against the phytopathogen Rhizoctonia solani AG-4 on Petri plates and in soybean roots, growth response and induction of PR-proteins were estimated after inoculation with P. aureofaciens 63-28 (P), with R. solani AG-4 (R), or with P. aureofaciens 63-28 + R. solani AG-4 (P + R). P. aureofaciens 63-28 showed strong antifungal activity against R. solani AG-4 pathogens in Petri plates. Treatment with P. aureofaciens 63-28 alone increased the emergence rate, shoot fresh weight, shoot dry weight and root fresh weight at 7 days after inoculation, when compared to R. solani AG-4; P + R treatment showed similar effects. Peroxidase (POD) and beta-1,3-glucanase activity of P. aureofaciens 63-28 treated roots increased by 41.1 and 49.9%, respectively, compared to control roots. POD was 26% greater in P + R treated roots than R. solani treated roots. Two POD isozymes (59 and 27 kDa) were strongly induced in P + R treated roots. The apparent molecular weight of chitinase from treated roots, as determined through SDS-PAGE separation and comparison with standards, was about 29 kDa. Five beta-1,3-glucanase isozymes (80, 70, 50, 46 and 19 kDa) were observed in all treatments. These results suggest that inoculation of soybean plants with P. aureofaciens 63-28 elevates plant growth inhibition by R. solani AG-4 and activates PR-proteins, potentially through induction of systemic resistance mechanisms.