The impacts of natural antioxidants on sclerotial differentiation and development in Rhizoctonia solani AG-1 IA

Rhizoctonia solani AG-1 IA, the pathogen of rice sheath blight (RSB), causes severe economic losses in all rice-growing countries or regions. The sclerotia produced by R. solani AG-1 IA play an important role in the disease cycle of RSB. In this study, the influences of three natural antioxidants (quercetin, morin and catechol) on sclerotial differentiation and development in R. solani AG-1 IA were investigated. Our results showed that quercetin, morin and catechol at lower concentration caused significant inhibitory effects on sclerotial differentiation as compared with thiourea, one of the most commonly used synthetic antioxidants and an effective inhibitor of sclerotial differentiation reported previously. Specifically, 0.30 mmol/L quercetin, 0.50 mmol/L morin and 1.80 mmol/L catechol resulted in 15 days, 11 days and 7 days delay of sclerotial differentiation, respectively; 0.14 mmol/L quercetin, 0.17 mmol/L morin and 1.00 mmol/L catechol caused 45 %, 32 %, and 33 % decrease of sclerotial dry weights, respectively, when compared with the untreated control. These potent antioxidative effects demonstrate that natural antioxidants have obvious advantages over the commonly used synthetic antioxidant, thiourea. Thus, natural antioxidants may have great potentials in effectively controlling RSB and related plant diseases caused by other sclerotium-producing fungi. In addition, our results also provide strong evidences to support the theory that sclerotial differentiation in sclerotium-producing fungi is induced by oxidative stress.