Diversity of Soilborne Oomycetes Associated with Industrial Hemp in Southeastern Pennsylvania: A Comparison of Metabarcoding Loci for Taxonomic Profiling

Industrial hemp was historically important as a fiber crop in Pennsylvania prior to the U.S. federal regulation of marijuana in the early twentieth century. The recent reestablishment of industrial hemp production, especially for cannabidiol extracts, necessitates a thorough evaluation of potential disease pressure from soilborne oomycetes. In this study, we used a combination of culture-dependent and metabarcoding methods to profile the taxonomic diversity of oomycetes associated with industrial hemp soils across six production fields in southeastern Pennsylvania during the 2022 growing season. We also assembled two separate mock communities to evaluate the performance of three metabarcode loci (nuclear internal transcribed spacer 1, mitochondrial cytochrome c oxidase subunit I, and mitochondrial rps10). The cytochrome c oxidase subunit I locus outperformed rps10 and internal transcribed spacer 1 by some metrics, but all three loci were sensitive to polymerase chain reaction artefacts and amplification bias in our mock community analysis. Overall, our results suggest the presence of at least 40 different oomycete species associated with hemp soils, of which 50% were recovered only in our metabarcoding analysis. Seven species were found in high abundance across all three metabarcode loci, including potential hemp pathogens Globisporangium ultimum and G. irregulare. This study provides an important resource for oomycete identification and industrial hemp management practices as cultivation continues to expand in Pennsylvania and elsewhere. [Formula: see text] Copyright © 2025 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .