Investigating binucleate Rhizoctonia induced defence responses in kidney bean against Rhizoctonia solani

Abstract

Four isolates of binucleate Rhizoctonia spp. (BNR), including AG-Bb, AG-Ba, AG-G and AG-A, were evaluated for pathogenicity on kidney beans. AG-Bb was the least virulent on kidney bean, and it was used as biocontrol agent against damping-off caused by Rhizoctonia solani AG-4 HG-II. The inoculation of the bean seedlings with BNR (AG-Bb) reduced disease symptoms in the following treatments: seedlings inoculated with BNR and R. solani simultaneously and also in seedlings inoculated with BNR and R. solani with a one-week interval. An investigation into different time points showed that BNR-induced resistance gradually decreased and disappeared after two weeks. Enzyme assays showed that the peroxidase (POX) and catalase (CAT) activities of bean seedlings increased after R. solani inoculation. The greatest activity of POX and CAT was discovered in seedlings inoculated with BNR and R. solani simultaneously. Reverse transcription-polymerase chain reaction (RT-PCR) analysis revealed a correlation between the expression of bean POX and CAT genes and the activity of the corresponding enzymes. The inoculation of leaf discs with BNR revealed the induction of resistance to R. solani. The leaf discs pretreated with sodium azide (NaN3) as POX and CAT inhibitors had less resistance to R. solani compared to the control. These results showed the importance of the former enzymes to induce resistance in bean plants. BNR inoculation leads to H2O2 accumulation in leaf discs which is the main reactive oxygen species (ROS). H2O2 can act as a defence signal and also lead to an increase in the solidity of cell walls. BNR stimulates bean seedlings to produce antioxidant enzymes and ROS which can increase bean resistance to R. solani.