The biocontrol potential of Pseudomonas fluorescens against Macrophomina phaseolina and estimating the total phenol compounds of bean roots

Charcoal rot caused by Macrophomina phaseolina is one of the most important soil borne diseases with a broad host range including bean, which annually brings a significant damage to this plant. Biological control of charcoal rot is very important because its chemical control harms the environment, microflora and soil fertility. Chemical control of charcoal rot is also difficult and sometimes ineffective. Fluorescent Pseudomonads are able to increase plant growth and inhibit the development of plant pathogens by producing and secreting antibiotics, enzymes, siderophores, and plant hormones. In this study, infected bean plants by M. phaseolina were collected from infected bean fields of Khorramabad (Lorestan Province, Iran) in the summer of 2015. Virulence of fungal isolates was evaluated in a greenhouse and one isolate with the highest pathogenicity was chosen for further experiments. The biocontrol potential of eight Pseudomonas fluorescens strains, whose biocontrol abilities were proved in previous studies, was examined against M. phaseolina in vitro. The growth inhibition of M. phaseolina was examined by dual culture test and the antifungal activity of bacterial volatile and nonvolatile metabolites. P. fluorescens UTPf125, which showed the highest inhibitory effect on the mycelial growth, was selected for greenhouse tests. UTPf125 strain led to a significant reduction (%50) of disease severity and increased fresh and dry weight significantly. Phenol compounds were evaluated 1, 3, 5, 7 and 9 days after inoculation by pathogen. The results showed that the highest value of total phenol content was obtained on the third and fifth days after inoculation, decreasing on the seventh and ninth days.