Alcohols and volatile organic acids as stimulants of rhizomorph production by Armillaria mellea.

To investigate symbiotic relationship of 'Chunma (Gastrodia elata) and the rhizomorph of Armillaria mellea, volatile organic acids and alcoholic compounds which were considered to be contained in Gastrodia elata were tested to determine stimulatory effects on rhizomorph growth on a chemically defined medium. Also, volatile organic acids were isolated from Gastrodia elata and analyzed by gas chromatography. The growth of rhizomorph was stimulated by the presence of alcohols and volatile organic acids, but acetic acid and methanol were ineffective. In the presence of valeric acid and ethanol, Armillaria mellea produced abundant rhizomorph at concentrations of 0.1 and 1%, respectively. Ethanol and valeric acid supplemented at regular intervals of 3 days as lower concentrations in the medium stimulated the growth of Armillaria mellea. The concentrations of ethanol and valeric acid as low at 0.01% added 3 days intervals for 15 days were more effective than initial concentrations of 0.1 and 1% in stimulating rhizomorph development of Armillaria mellea. Eight kinds of volatile organic acids were identified and quantified by gas chromatography. The major compounds were n-propionic, valeric, iso-carproic and caproic acids, and the minor compounds were iso-butyric, butyric, iso-valeric and hepatanoic acids. Valeric acid was the most abundant among them.