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 usual preys, in contrast to higher toxicity to non-prey similar species (Heatwole and Powell, 1998. Resistance of eels (Gymnothorax) to the venom of sea kraits (Laticauda colubrina): a test of coevolution. Toxicon 36, 619-625). In an attempt to examine whether such coevolutionary discrepancies also occur in plant host-parasite interactions, two strains of Ceratocystis grown on artificial medium, C. fimbriata, parasite of the plane tree, and C. bruneociliata, parasite of the Scots pine (Pinus sylvestris), were compared for growth parameters, in controls and in presence of various concentrations of coniferyl alcohol (a phenolic derivative previously found to be released following inoculation of pine trees with C. bruneociliata). Coniferyl alcohol differently inhibited the growth of both fungi. In the case of the conifer-specific fungus, inhibition rate was less marked at low doses (<2.5 mM) but it rose more steeply at higher doses (10 mM) after a sigmoidal transition at around 3.2 mM, indicating a physiological threshold. These results support the hypothesis of a specific action of coniferyl alcohol against C. Bruneociliata, as a coevolutionary adaptative characteristics of the fungus.