Genotypic diversity, phylogeography, and population structure of two lineages of Phaeocryptopus gaeumannii in the Pacific Northwest

The ascomycete fungus Phaeocryptopus gaeumannii is the causal organism of Swiss needle cast (SNC), a foliage disease of Douglas-fir (Pseudotsuga menziesii). The disease was first described in forest plantations in Europe in the 1920s (Boyce 1940). It has since been determined that P. gaeumannii is endemic to western North America and the native range of Douglas-fir in the northwestern United States. Initial assessments of genetic diversity and population structure performed using molecular markers known as single strand conformation polymorphisms (SSCPs) indicated the presence of two distinct sympatric populations (lineages) of the fungus in the Pacific Northwest (Winton et al. 2006). Subsequently a set of more variable molecular markers, microsatellites or short sequence repeats (SSRs), that permit more fine-scale analysis of P. gaeumannii populations were developed by Winton et al. (2007), but intensive sampling and analyses using these markers were not undertaken until now.