Antifungal properties of terpenoids in Picea abies against Heterobasidion parviporum

The antifungal properties of 14 major oleoresin-constitutive terpenoids of Norway spruce (Picea abies) against Heterobasidion parviporum were evaluated in vitro at three gradient concentrations, 0.1, 0.2 and 0.4 mu mol/cm(2), on potato dextrose agar medium. Eight monoterpene hydrocarbons (+)- and (-)-alpha-pinene, (-)-beta-pinene, (+)-3-carene, myrcene, (+)- and (-)-limonene, terpinolene; four oxygenated monoterpenes alpha-terpineol, terpinen-4-ol, 1,8-cineole, bornyl acetate; and two resin acids abietic acid and dehydroabietic acid were selected. Abietic and dehydroabietic acids showed the highest antifungal activities at all concentrations. Among oxygenated monoterpenes, bornyl acetate and alpha-terpineol showed antifungal activity at the highest concentration. Among monoterpene hydrocarbons, (+)-alpha-pinene showed similar activity to terpinen-4-ol and 1,8-cineole at the highest concentration; however, it was lower than alpha-terpineol and bornyl acetate. Other monoterpene hydrocarbons inhibited mycelial growth by <10%. Re-extraction of medium surfaces after the test period revealed that most alpha-terpineol and terpinen-4-ol remained unchanged on the surface but monoterpene hydrocarbons completely disappeared. However, notable fungal transformed products were observed on surfaces applied with 1,8-cineole and bornyl acetate. Thus, mycelial growth inhibition of monoterpenoids might be caused by complex functions such as biodegradation and/or detoxification by interaction between mycelium and compound. These results provide a basis for future studies considering the role of chemodiversity in the comprehensive chemical defence of P. abies.