Effects of the Plant Defence Inducer, Acibenzolar‐S‐Methyl, on Hypocotyl Rot of Soybean Caused by Rhizoctonia solani AG‐4

The plant defence inducer, acibenzolar‐S‐methyl (ASM) was tested for its ability to protect soybean against hypocotyl rot caused by Rhizoctonia solani Kühn AG‐4. ASM in vitro exhibited an antifungal dose‐dependant activity in the form of reduced mycelial growth. This inhibition reached 40% in comparison with the control at a concentration of 0.5 g/l ASM in the growth media. Seed imbibition with ASM at a concentration of 0.08 g/l and 0.5 g/l significantly induced a reduction of the intensity of hypocotyl rot symptoms caused by R. solani AG‐4 that was correlated with a stimulation of chitinase activity. The protective effect of ASM against R. solani AG‐4 is probably due to the combination of induced resistance and its effect on pathogen growth. Seed treatment with ASM affected also the growth of 2‐day‐old seedlings. A dose‐dependant inhibition of the seminal root growth was observed which reached 53% at a concentration of 0.5 g/l ASM. This growth reduction of soybean was transitional and was rapidly recovered in optimal growth conditions except at 0.5 g/l of ASM.