Evaluation of plant-growth-promoting rhizobacteria, acibenzolar-S-methyl and hymexazol for integrated control of Fusarium crown and root rot on tomato

BACKGROUND: Plant growth-promoting rhizobacteria (PGPR) can be potential agents for biological control of plant pathogens, while their combined use with conventional pesticides may increase their efficacy and broaden the disease control spectrum. The effect of four different Bacillus sp. PGPR strains (B. subtilis GB03 and FZB24, B. amyloliquefaciens IN937a and B. pumilus SE34) applied individually and in mixtures, as well as in combined use with acibezolar-S-methyl (ASM) and hymexazol, on plant growth promotion and on the control of Fusarium crown and root rot (FCRR) of tomato was evaluated. RESULTS: All PGPR strains promoted the tested plant growth characteristics significantly. A higher promoting effect was provided by SE34. Experiments on population dynamics of PGPR strains revealed that, after 28 days of incubation, populations of strain SE34 remained stable, while the remaining bacterial strains showed a slight decline in their population densities. The GB03 and FZB24 strains provided a higher disease suppression when applied individually. However, application of IN937a in a mixture with GB03 provided a higher control efficacy of Fusarium oxysporum f. sp. radicis-lycopersici (Forl). Treatment of tomato plants with ASM resulted in a small reduction in disease index, while application of hymexazol provided significantly higher control efficacy. Combined applications of the four PGPR strains with either ASM or hymexazol were significantly more effective. CONCLUSION: The results of the study indicate that, when bacilli PGPR strains were combined with pesticides, there was an increased suppression of Forl on tomato plants, and thus they may prove to be important components in FCRR integrated management. (C) 2011 Society of Chemical Industry