Occurrence of Plant-Parasitic Nematodes in Pacific Northwest Hopyards

The Pacific Northwest (PNW) of the United States (Idaho, Oregon, and Washington) is the most important hop-producing region both nationally and internationally. However, little research on plant-parasitic nematodes has been conducted in the region. In this study, a total of 185 soil samples representing 93 hopyards were collected in 2021 and 2022 to characterize the plant-parasitic nematodes associated with this crop in the PNW. Ten different genera of plant-parasitic nematodes were found, with the hop cyst nematode, Heterodera humuli, second-stage juveniles (J2s) being the most frequently encountered (54% of the total samples and 65% of surveyed hopyards). The identity of selected H. humuli populations was confirmed by Sanger sequencing of the 28S rRNA gene. Other nematode taxa encountered in order of frequency of occurrence were Helicotylenchus, Telotylenchinae, Xiphinema, Paratylenchus, Pratylenchus, Trichodoridae, Ditylenchus, Gracilacus, and Mesocriconema. Heterodera humuli J2 densities were positively correlated with sand content based on the Spearman correlation coefficient. The host status of four hop cultivars (‘Cascade’, ‘Centennial’, ‘Mosaic’, and ‘Citra’) to three Meloidogyne species was also assessed under greenhouse conditions. Meloidogyne incognita reproduced on all four hop cultivars, with reproduction factor values (RF = final population density/initial population density) ranging from 5 to 40. The hop cultivars were non-hosts for M. chitwoodi (RF ≤ 0.1) and varied from non-host to host (RF = 0.1 to 3) for M. hapla. This study demonstrates the wide distribution of the most important plant-parasitic nematode in hop production, H. humuli, in the PNW and the host status of hop cultivars to different Meloidogyne spp.