Genetic and Phenotypic Characterization of the Fungal Pathogen from Western Colorado Peach Orchards and the Development of a ddPCR Assay for Detection and Quantification.

Cytospora canker is one of the most important diseases affecting peach production in Colorado, yet previous efforts to characterize species diversity in Colorado have relied exclusively on morphological traits. Recently, several new species were described from peach orchards within the United States using molecular and morphological data, prompting the need to reexamine spp. present on peach trees in Colorado. A total of 137 isolates of spp. were collected from eight orchards in western Colorado. Isolates were sequenced at the internal transcribed spacer region and elongation factor 1-α and assessed with reference sequences in phylogenetic analyses. All isolates from western Colorado peach trees resolved with the newly described . In addition to molecular characterization, temperature growth and virulence assays were conducted to assess phenotypic variation among the isolates from western Colorado. Variation across isolates was found both in growth at different temperatures and in virulence. Ancestral state reconstruction analyses resolved the most virulent (and most often collected) haplotypes together in a well-supported clade from which a single monophyletic origin of high virulence can be inferred. Finally, a droplet digital PCR assay was developed for use in ongoing and future studies to detect and quantify from field and laboratory samples.