Coevolutionary toxicity as suggested by differential coniferyl alcohol inhibition of ceratocystis species growth

Coevolution has been shown to lower the toxicity of predator venoms to usua l preys, in contrast to higher toxicity to non-prey similar species (Heatwo le and Powell, 1998. Resistance of eels (Gymnothorax) to the venom of sea k raits (Laticauda colubrina): a test of coevolution. Toxicon 36, 619-625). I n an attempt to examine whether such coevolutionary discrepancies also occu r in plant host-parasite interactions, two strains of Ceratocystis grown on artificial medium, C. fimbriata, parasite of the plane tree, and C. bruneo ciliata, parasite of the Scots pine (Pinus sylvestris), were compared for g rowth parameters, in controls and in presence of various concentrations of coniferyl alcohol (a phenolic derivative previously found to be released fo llowing inoculation of pine trees with C. bruneociliata). Coniferyl alcohol differently inhibited the growth of both fungi. Tn the case of the conifer -specific Fungus, inhibition rate was less marked at low doses (< 2.5 mM) b ut it rose more steeply at higher doses (10 mM) after a sigmoidal transitio n at around 3.2 mM, indicating a physiological threshold. These results sup port the hypothesis of a specific action of coniferyl alcohol against C. Br uneociliata, as a coevolutionary adaptative characteristics of the fungus. (C) 2000 Elsevier Science Ltd. All rights reserved.