Soil amended with Brassica juncea plant tissue reduces sclerotia formation, viability and aggressiveness of Rhizoctonia solani AG1-IA towards rice

Brassica juncea plant tissue rich in glucosinolates has been used as a soil biofumigant for control of soilborne pathogens. Biocidal effects are attributed to volatile allyl isothiocyanate released upon hydrolysis of glucosinolates. In vitro inhibition of the mycelium growth of Rhizoctonia solani by B. juncea is well documented. The objective of this study was to determine the impacts of B. juncea as a soil amendment on the viability, aggressiveness, and sclerotia formation of R. solani AG1-IA, the causal agent of sheath blight in rice (Oryza saliva). In laboratory experiments, the effects of B. juncea amendment rate (0, 0.2, 0.4, 0.8, 1.6 or 3.2% wt/wt) and duration of exposure (7, 14, or 28 days) on R. solani AG1-IA were evaluated. Mycelium exposed to soils amended with B. juncea at 0.2-3.2% with 7, 14 or 28 days of exposure resulted in significantly reduced sclerotia formation when compared to the mycelium exposed to the non-amended soil. The viability of sclerotia after exposure for 14 and 28 days to soils amended with 1.6 and 3.2% of B. juncea was significantly lower than that of sclerotia exposed to non-amended soil. Sclerotia or mycelium exposed to soil amended with 3.2% of B. juncea for 28 days, resulted in a reduction in aggressiveness as shown by smaller sheath blight lesion development on detached rice leaves than the non-treated controls. Results of this study demonstrate for the first time that B. juncea soil amendment can reduce the viability and aggressiveness of mycelium and sclerotia and further affect the formation of sclerotia of R. solani. The reduction of sclerotia formation by B. juncea introduction may result in the reduction of primary inoculum of sheath blight in the following rice season. Published by Elsevier Ltd.