Investigating the correlation between endorhizosphere population of Pseudomonas fluorescens biocontrol agent of Rhizoctonia solani and number of nitrogen-fixing bacteria nodes in bean root

Bean is one of the most important members of Fabaceae, which is in a symbiosis with rhizobia, a species of atmospheric nitrogen-fixing bacteria. These bacteria establish nodes in bean roots and it’s effective in soil fertility. Yearly, after bean harvesting, large quantities of nitrogen are added to the soil. Rhizoctonia solani the causal agent of Rhizoctonia root and collar rot is one of the most important diseases of the bean. Because of being a soil-borne pathogen, a wide range of hosts and high degrees of aggressiveness, its managing is difficult. The use of antagonistic microorganisms, especially Pseudomonas fluorescens, against it has been investigated as a promising control method. In this study, infected bean seedlings with R. solani were collected from Khomein. Virulence of fungal isolates was evaluated in the greenhouse, then a fungus isolate with the highest pathogenicity was chosen for next experiments. The biocontrol ability of 8 P. fluorescens strains against R. solani was examined in vitro. P. fluorescens P13, which was the most effective in controlling the pathogen in all experiments, was selected for next. For greenhouse studies, roots of bean seedlings were treated with 108 cfu/ml of P13. The results showed that biocontrol bacteria caused a 50% reduction in disease severity of Rhizoctonia rot. The endorhizospher population of P13 and number of Rhizobium nodes were evaluated in 15, 30 and 45 days after inoculation. Although, as time passed by, the population of P13 in the endorhizosphere decreased, but in the 45th day, a high population of this antagonist, about 3.2 × 105 cells bacteria/gr fresh root, recovered in bean endorhizosphere, which compared to the control plant, caused about 72% reduction in the number of Rhizobium nodes. In this interaction, the number of Rhizobium nodes decreased significantly, but no significant difference was observed in the dry weight of the treated plants and controls.

کلیدواژه ها:

Nitrogen-fixing bacteria ، Biocontrol ، Endorhizosphere