Pratylenchus pseudocoffeae Mizukubo, 1992 infecting dahlia (Dahlia hybrida) in the United States expands its known host and geographic ranges

Pratylenchus pseudocoffeae is a migratory endoparasitic nematode with a limited documented geographic distribution and host range. We studied nine putative P. pseudocoffeae populations recovered from symptomatic dahlia (Dahlia hybrida) tubers in Ohio and Pennsylvania and evaluated their pathogenicity. Two populations were selected for integrative characterization using morphological and molecular analysis, whereas the remaining populations were identified molecularly based on two ribosomal DNA loci (i.e., internal transcribed spacer and large subunit regions). All populations were confirmed as P. pseudocoffeae, representing the first report of this species in Ohio and Pennsylvania, and the first report of dahlia as a natural host. Pathogenicity was assessed under greenhouse conditions by inoculating rooted dahlia cuttings with initial soil densities of 0, 7, 14, and 28 nematodes cm⁻³ soil. Inoculated plants exhibited significant reductions in root biomass (61–75%) relative to noninoculated controls. Taken together, these results demonstrate that dahlia is a suitable host of P. pseudocoffeae, contributing to a better understanding of the distribution of this species in North America, and provide molecular diagnostic data to support accurate nematode identification for future diagnostic and epidemiological studies.