Plant-parasitic Nematodes on Hemp in the Pacific Northwest of the United States

Background Plant-parasitic nematodes are one of the most important biotic factors that impact crop production globally. Since hemp cultivation in the U.S. was banned from 1970 to 2018, little information is available about current plant-parasitic nematode pressure on U.S. hemp production. The production of hemp has gained interest in Washington and Oregon, states where several genera of plant-parasitic nematodes have been associated with various crops. This report is the first to define plant-parasitic nematodes associated with hemp in these states in the Pacific Northwest. Methods Soil and root samples from hemp fields were collected in early autumn in 2021, 2022, and 2023. The occurrence, population density, and identity of plant-parasitic nematodes in these samples were determined using morphological and molecular identification methods. A Bayesian analysis of available sequence data was used to analyze phylogenetic relationships of nematode species found in hemp fields. Additionally, the host status of hemp ‘Alpha Explorer’ to three plant-parasitic nematodes, Meloidogyne chitwoodi,M. hapla, and Pratylenchus neglectus, was tested under greenhouse conditions. The occurrence of plant-parasitic nematodes and reproduction factor values of the three nematode species were analyzed with non-parametric methods. Results Pratylenchus spp. were the most frequent plant-parasitic nematodes recovered from soil samples, being present in 64 % of samples (n = 89). Only two endoparasitic nematodes, Meloidogyne spp. and Pratylenchus spp., were found in root samples with Pratylenchus spp. as the most frequent (30 out of 37 samples). A large diversity of Pratylenchus spp. was detected in hemp root samples. Hemp ‘Alpha Explorer’ was a poor host for Pratylenchus neglectus, resulting in low reproduction values (< 1). Additionally, results of our study indicated that hemp is not a host for Meloidogyne chitwoodi. Conclusions Pratylenchus spp. are the most important plant-parasitic nematodes found in hemp fields in Oregon and Washington. This study reports for the first time, five Pratylenchus species (Pratylenchus crenatus, P. fallax, P. hexincisus, P. neglectus, and P. scribneri) associated with hemp in Oregon and Washington; P. penetrans was also found in the region on hemp plants. The host status results indicate that hemp can be considered a non-host for M. chitwoodi and a poor host for M. hapla and P. neglectus.