2018 ASHS Annual Conference

Sulfur has been used to control plant pathogens such as Uncinula necator and Botrytis cinerea. Sulfur compounds such as allyl-isothiocyanate are registered as fumigants, but some sulfur compounds have not been tested against soilborne pests. The objective of this study was to test the antifungal activity of allyl-isothiocyanate (commercial name: Dominus), water and ethanolic extracts of mustard seed meal (MSM), and allicin against mycelial growth and sclerotial germination of Sclerotinia minor which can cause significant economic losses in lettuce fields. MSM was extracted by distilled water (1:5) or 99% ethanol (1:5, 1:2.5, and 1:1.25). The extract of one mL was added to 100 ml potato dextrose agar for the agar dilution test. The concentrations of allicin and allyl-isothiocyanate were 5.4, 10.8, and 14.4 mg mL^-1 and 10, 50, 100, and 500 µL mL^-1, respectively. As the concentration of ethanolic extract of MSM and allicin increased, the mycelial growth and sclerotial germination of S. minor decreased significantly. Allyl-isothiocyanate at 500 µL mL^-1 completely inhibited the mycelial growth and sclerotial germination of S. minor. To verify the effectiveness of short-time exposure of the sulfur compounds, the sclerotia were dipped into aqueous solution of the sulfur compounds for one minute. The sclerotial germination was inhibited by allyl-isothiocyanate, ethanolic extract of MSM, and allicin until the fourth day after the dipping. The results indicated that the sulfur compounds, except water extract of MSM, demonstrated antifungal activity against the growth and germination of S. minor, and the compounds may be potential sources of natural fungicides and fumigants. Further investigation is needed to increase the duration of effective control.