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 Ku¨ hn 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