Potential of Allyl Isothiocyanate to Control Rhizoctonia solani Seedling Damping Off and Seedling Blight in Transplant Production

The synthetic mustered flavouring essential oil, allyl isothiocyanate (AITC), was evaluated for its effect on suppression of Rhizoctonia solani growth in vitro, and in field soils for reducing inoculum density, saprophytic substrate colonization and seedling damping off and blight using snap bean and cabbage as indicator plants. In vitro growth was completely inhibited at the concentration of 50 ll/l. Inoculum density and saprophytic substrate colonization by the fungus in soil were not affected by AITC concentrations of 50 or 75 ll/kg soil. The inoculum density estimation by the use of soil-drop technique created an artefact leading to an erroneous conclusion that the fungus was eradicated from soil within 1–3 days after AITC treatment at 150 or 200 ll/kg soil. The saprophytic substrate colonization showed that although the activity of R. solani was greatly reduced, the fungus still colonized 45% of the substrate units at these concentrations, and up to 100% at lower concentrations within 1 day after treatment. At higher concentrations the recovery rate from the substrates gradually declined over time to <6%. Drenching R. solani infested sandy-loam or silty-clay-loam soil with water containing the emulsified AITC to provide 150 or 200 ll/l soil, a few days prior to planting, gave over 90% disease control in snap bean and cabbage, with no apparent phytotoxic effect. The effect of AITC was not influenced by the physical soil texture. AITC appears to have a good potential to replace methyl bromide fumigation of the substrate used for transplant production.