Pathogenicity of ganoderma species on landscape trees in the Southeastern United States

The genus Ganoderma contains species that are associated with dead and declining host trees. Many species have been described as pathogens in literature, because anecdotally, the presence of fruiting bodies on living trees has been widely associated with a general decline in tree health. Few studies have investigated the pathogenicity of Ganoderma species on landscape trees in the southeastern U.S. Pathogenicity tests were used to determine the pathogenicity of G. curtisii, G. meredithiae, G. sessile, and G. zonatum on young, healthy landscape trees (Pinus elliottii var. elliottii, P. taeda, Quercus shumardii, Q. virginiana, and Butia odorata) common to the southeastern U.S. Inoculations were made by drilling into the sapwood of the lower bole and inserting wooden dowels that were infested with each Ganoderma species. In two field experiments, 11 to 12 months post inoculation, trees had no visual, external symptoms of disease. There were differences in the extent of internal xylem discoloration near the site of inoculation in comparison with the mock-inoculated control in experiment 1, but there were no differences relative to the control in experiment 2. In both experiments, G. sessile was the only species that was successfully reisolated from the pine and oak hosts. Although disease symptoms were not obvious, the reisolation of G. sessile outside the inoculation point was a significant finding, and suggests that this species was capable of infecting healthy sapwood. G. sessile constitutively produces chlamydospores within its vegetative mycelium, which may contribute to its persistence in the discolored sapwood. These data suggest that the Ganoderma species tested, following trunk wounding, are not pathogens of young, actively growing landscape trees that only possess sapwood. The establishment of these fungi using alternative infection courts (e.g., roots) and their interactions in older living trees (e.g., trees with heartwood) needs investigation to better understand their effects on tree health.