Elucidating "lucidum": Distinguishing the diverse laccate Ganoderma species of the United States.

Ganoderma is a large, diverse and globally-distributed genus in the Basidiomycota that includes species causing a white rot form of wood decay on a variety of tree species. For the past century, many studies of Ganoderma in North America and other regions of the world have used the name G. lucidum sensu lato for any laccate (shiny or varnished) Ganoderma species growing on hardwood trees or substrates. Molecular studies have established that G. lucidum sensu stricto (Curtis) Karst is native to Europe and some parts of China. To determine the species of the laccate Ganoderma that are present in the United States, we studied over 500 collections from recently collected samples and herbarium specimens from hardwoods, conifers, and monocots. A multilocus phylogeny using ITS, tef1α, rpb1 and rpb2 revealed three well-supported clades, similar to previously reported findings. From the U.S. collections, thirteen taxa representing twelve species were identified, including: G. curtisii, G. lucidum sensu stricto, G. martinicense, G. oregonense, G. polychromum, G. ravenelii, G. sessile, G. tsugae, G. tuberculosum, G. cf. weberianum, G. zonatum, and Tomophagus colossus (syn. G. colossus). The species G. meredithiae is synonymized with G. curtisii, and considered a physiological variant that specializes in decay of pines. The designation G. curtisii f.sp. meredithiae forma specialis nov. is proposed. Species such as G. curtisii and G. sessile, once considered as G. lucidum sensu lato, were found to be divergent from one another, and highly divergent from G. lucidum sensu stricto. Morphological characteristics such as context tissue color and features (e.g. melanoid bands), basidiospore shape and size, geographic location, and host preference were found to aid in species identification. Surprisingly, G. lucidum sensu stricto was found in the U.S., but only in geographically restricted areas of northern Utah and California. These collections appear to have resulted from the introduction of this species into the United States possibly from mushroom growers producing G. lucidum outdoors. Overall, this study clarifies the chaotic taxonomy of the laccate Ganoderma in the United States, and will help to remove ambiguities from future studies focusing on the North American species of laccate Ganoderma.

A unique species in Phytophthora clade 10, Phytophthora intercalaris sp. nov., recovered from stream and irrigation water in the eastern USA.

A novel species of the genus Phytophthora was recovered during surveys of stream and nursery irrigation water in Maryland, Massachusetts, North Carolina, Virginia and West Virginia in the USA. The novel species is heterothallic, and all examined isolates were A1 mating type. It produced rare ornamented oogonia and amphigynous antheridia when paired with A2 mating type testers of Phytophthora cinnamomi and Phytophthora cryptogea. Sporangia of this novel species were non-papillate and non-caducous. Thin-walled intercalary chlamydospores were abundant in hemp seed agar and carrot agar, while they were produced only rarely in aged cultures grown in clarified V8 juice agar. Phylogenetic analyses based on sequences of the internal transcribed spacer region and the ß-tubulin and mitochondrial cytochrome-c oxidase 1 (cox1) genes indicated that the novel species is phylogenetically close to Phytophthora gallica in Phytophthora clade 10. The novel species has morphological and molecular features that are distinct from those of other species in Phytophthora clade 10. It is formally described here as Phytophthora intercalaris sp. nov. Description of this unique clade-10 species is important for understanding the phylogeny and evolution of Phytophthora clade 10.

Phytophthora Populations in Nursery Irrigation Water in Relationship to Pathogenicity and Infection Frequency of Rhododendron and Pieris.

Phytophthora spp. are waterborne plant pathogens that are commonly found in streams, rivers, and reclaimed irrigation water. Rhododendron and Pieris trap plants at two commercial nurseries were irrigated with water naturally infested with Phytophthora spp. during the 2011 and 2012 growing seasons to assess the frequency of disease. Phytophthora spp. were consistently recovered from water samples at every collection time but detected on only 2 of the 384 trap plants during the two growing seasons. Pathogenicity assays proved that Phytophthora hydropathica and Phytophthora taxon PgChlamydo, commonly recovered taxa in irrigation water at the nurseries, were foliar pathogens of Rhododendron and Pieris; however, neither species was able to cause root rot on these same hosts. Overall, Phytophthora spp.-infested irrigation water did not act as a primary source of infection on Rhododendron and Pieris, even though foliar pathogenic species of Phytophthora were present in the water.