Various essential oils, organic acids, Biosept, (grapefruit extract), Tillecur and extracts of stinging nettle and golden rod were tested for their antimicrobial properties in order to disinfect vegetable seed. In in vitro assays, thyme oil, oregano oil, cinnamon oil, clove oil and Biosept had the highest activity against the seed borne pathogens Xanthomonas campestris pv. campestris, Clavibacter michiganensis subsp. michiganensis, Alternaria dauci and Botrytis aclada. Low antimicrobial activity wasfound for the organic acids against the fungal pathogens. Seed treatment for 0.5 h with selected essential oils or Biosept in concentrations between 0.1 and 1% eliminated > 99% of total bacteria associated with cabbage seed. It also reduced the percentage of seeds contaminated with fungi in blotter tests from 70% to less than 10%. Extended periods of treatment did not significantly improve results. Cinnamon oil and Biosept used in concentrations exceeding 1% had a negative effect on seed germination. Antimicrobial effects with organic acids were variable, but in general, the organic acids ascorbic acids, propionic acid, acetic acid and lactic acid at concentrations of 2.5% or higher, reduced seed-associated bacteria. Of the organic acids, only propionic acid reduced seed germination at a concentration higher than 1%. Thyme oil was considered the most promising natural compound for reducing seed borne pathogens in seed.
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