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Research Project: Development of Knowledge-based Approaches for Disease Management in Small Fruit and Nursery Crops

Location: Horticultural Crops Research

Title: First report of the hop cyst nematode, heterodera humuli, in two counties of the Yakima Valley region, WA, USA

Author
item DARLING, E - Michigan State University
item PU, J - Michigan State University
item COLE, E - Michigan State University
item PERRAULT, J - Yakima Chief Ranches
item CHRISTIAN, R - Yakima Chief Ranches
item HALE, A - Yakima Chief Ranches
item WARNER, F - Michigan State University
item Zasada, Inga
item CHUNG, H - Michigan State University
item QUINTANILLA, M - Michigan State University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2021
Publication Date: 3/23/2021
Citation: Darling, E., Pu, J., Cole, E., Perrault, J., Christian, R., Hale, A., Warner, F., Zasada, I.A., Chung, H., Quintanilla, M. 2021. First report of the hop cyst nematode, heterodera humuli, in two counties of the Yakima Valley region, WA, USA. Plant Disease. 105(4):727-738. https://doi.org/10.1094/PDIS-08-20-1769-PDN.
DOI: https://doi.org/10.1094/PDIS-08-20-1769-PDN

Interpretive Summary: This is a first report of the hop cyst nematode, a microscopic roundworm, in hops in two counties in Washington. Washington state is the number one producer of hops in the United States. The hop cyst nematode was shown to reduce plant growth by 40%. This first report is of significance because it indicates the presence of this nematode in two counties where most of the hops is produced in the state.

Technical Abstract: America is the top hop producing country worldwide, with 75% of production occurring in Washington state, with the majority of this production occurring in the Yakima Valley region . In late 2019, 30 soil samples from 15 different fields were collected from hops. Twenty of these samples contained at least one cyst and 23 contained at least one juvenile. Body length of juveniles (n = 5) averaged 377.62 ± 4.76 µm which is consistent with H. humuli juvenile body measurements . Three samples from Yakima County and two from Benton County were identified to the species level using sequences from the internal transcribed spacer (ITS) region of the 5.8S gene. Sequence comparison with available ITS (5.8S) in GenBank using BLAST showed 99.85% identity to H. humuli for all five samples. To confirm pathogenicity, eight 1-gal pots were filled with a 90:10 play sand to potting soil mixture and one hop rhizome cv. ‘Centennial’ was planted in pots and maintained in a greenhouse. After above ground plant growth was observed, half the pots were inoculated with hand-picked H. humuli cysts from Yakima soil samples at a density of 10 cysts/100 cc of soil. Forty-five days after inoculation, five 100 cc soil samples from each pot were collected and plant measurements were recorded. Soil samples revealed that H. humuli populations had an average Reproductive Factor (RF = final nematode population/initial nematode population) of 2.08. Bine heights were reduced by an average of 40.4% in pots inoculated with H. humuli compared to control plants (P=0.0016). IThis is a significant finding that greatly impacts the Washington state hop industry. Due to the lack of known effective nematode control measures, the discovery of H. humuli in the major hop-growing region of Washington warrants concern.