Phytoalexin production by Aspen (Populus tremuloides Michx.) in response to infection by Hypoxylon mammatum (Wahl.) Mill and Alternaria spp.

Freshly wounded stem sections of P. tremuloides Michx. produce phytoalexin when inoculated with mycelium of Hypoxylon mammatum (Wahl.) Mill., and Alternaria sp. These exudates are inhibitory against spore germination of these two fungi and, although inhibitory against mycelial growth of Alternaria sp., have no effect on the mycelial growth of H. mammatum. It was possible to correlate the amount of phytoalexin elicited by different strains with the inhibitory activity.