Cultural characterization and chlamydospore function of the Ganodermataceae present in the eastern United States.

The cultural characteristics of fungi can provide useful information for studying the biology and ecology of a group of closely related species, but these features are often overlooked in the order Polyporales. Optimal temperature and growth rate data can also be of utility for strain selection of cultivated fungi such as reishi (i.e., laccate Ganoderma species) and potential novel management tactics (e.g., solarization) for butt rot diseases caused by Ganoderma species. Historically, the taxonomy of the laccate (shiny) Ganoderma species has been unresolved and many species have been treated together as G. lucidum. The cultural characteristics of Ganoderma species from the United States are needed to understand the biology of these unique species that have all been lumped under this name. Culture morphology, average growth rate, optimal temperatures, and resiliency to elevated temperature exposure were characterized for isolates of Ganodermataceae taxa from the eastern United States, including Ganoderma curtisii, G. martinicense, G. meredithiae, G. ravenelii, G. sessile, G. tsugae, G. tuberculosum, G. cf. weberianum, G. zonatum, and Tomophagus colossus. We documented differences in linear growth rates and optimal temperatures between taxa. Isolates of G. sessile and T. colossus grew the fastest, and isolates of G. meredithiae, G. ravenelii, and G. tsugae grew the slowest. Isolates of G. sessile, G. martinicense, G. cf. weberianum, and T. colossus constitutively produced chlamydospores on malt extract agar, and these species were the only species to survive long-term exposure (30 or 40 d) to 40 C. We hypothesize that chlamydospores function as survival structures that serve as propagules resilient to adverse temperature conditions, especially heat. Cultural characteristics of G. martinicense, G. ravenelii, G. tuberculosum, and G. cf. weberianum collected from the United States are described for the first time.

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.

Elucidating wood decomposition by four species of Ganoderma from the United States.

The laccate (shiny or varnished) Ganoderma contain fungi that are important wood decay fungi of living trees and decomposers of woody debris. They are also an important group of fungi for their degradative enzymes and bioprocessing potential. Laboratory decay microcosms (LDMs) were used to study the relative decay ability of G anoderma curtisii, Ganoderma meredithiae, Ganoderma sessile, and G anoderma zonatum, which are four commonly encountered Ganoderma species in the U.S., across four wood types (Pinus taeda, Quercus nigra, Q uercus virginiana, and Sabal palmetto). Generally, all Ganoderma species were able to decay all types of wood tested despite not being associated with only certain wood types in nature. G. sessile, on average caused the most decay across all wood types. Among the wood types tested, water oak (Q. nigra) had the most mass loss by all species of Ganoderma. Scanning electron microscopy was used to assess micromorphological decay patterns across all treatments. All Ganoderma species simultaneously decayed wood cells of all wood types demonstrating their ability to attack all cell wall components. However, G. zonatum caused selective delignification in some sclerenchyma fibers of the vascular bundles in palm (S. palmetto) as well as in fibers of water oak. In addition, G. zonatum hyphae penetrated fibers of palm and oak wood causing an unusual decay not often observed in basidiomycetes resulting in cavity formation in secondary walls. Cavities within the secondary walls of fibers gradually expanded and coalesced resulting in degradation of the S2 layer. Differences in colony growth rates were observed when Ganoderma species were grown on medium amended with water soluble sapwood extracts from each wood type. G. meredithiae had enhanced growth on all media amended with sapwood extracts, while G. curtisii, G. sessile and G. zonatum had slower growth on loblolly pine extract amended medium.