Investigating the effect of flavonoids in induction of resistance in the bean plant against crown and root rot caused by Rhizoctonia solani

In this research, pathogenicity tests were done using two different methods including inoculation of leaf discs under laboratory conditions and infecting the seedlings in the greenhouse in order to determine resistance levels of bean cultivars to Rhizoctonia solani AG4 HG-II, the causal agent of the crown and root rot. Furthermore,the most susceptible bean cultivar (cv. Naz, because of economic justification) was used to examine the possibility of inducing resistance against the pathogen, using flavonoids such as quercetin and naringenin and investigate some mechanisms involved in induced resistance. To study the effects of different concentrations of flavonoids in the induction of resistance in bean against R. solani, the seedlings were treated with 100 to 400 μg/mL concentrations of flavonoids. The treated and control plants were inoculated with the pathogen and the disease index was calculated one week following inoculation. Results showed that various concentrations of quercetin and naringenin had different effects in reducing the disease index. Quercetin at 200 to 400 μg/mL significantly decreased the progression of the disease caused by R. solani in the bean. The best time interval between treatment and inoculation was 3 days. Naringenin at 100 and 200 μg/mL and quercetin at 100 μg/mL did not significantly reduce the disease progression. Investigating callose, superoxide, and hydrogen peroxide levels at various time points after R. solani inoculationin the seedlings pretreated with quercetin revealed that quercetin-induced resistance in bean against the fungal pathogen via priming the defense components.