Trends in occurrence, distribution, and population densities of plant-parasitic nematodes in the Pacific Northwest of the United States from 2012 to 2016

Authors: Zasada, Inga; Kitner, Megan; WRAM, CATHERINE - Oregon State University; WADE, N - Oregon State University; INGHAM, R - Oregon State University; HAFEZ, S - University Of Idaho; MOJTAHEDI, HASSAN - Agnema, Llc; CHAVOSHI, S - Agnema, Llc; HAMMACK, N - Ever-Green Nematode Testing Labs, Inc

Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/11/2019
Publication Date: 2/15/2019
Citation: Zasada, I.A., Kitner, M.L., Wram, C., Wade, N., Ingham, R.E., Hafez, S., Mojtahedi, H., Chavoshi, S., Hammack, N. 2019. Trends in occurrence, distribution, and population densities of plant-parasitic nematodes in the Pacific Northwest of the United States from 2012 to 2016. Plant Health Progress. 20(1):20-28. https://doi.org/10.1094/PHP-11-18-0077-RS.
DOI: https://doi.org/10.1094/PHP-11-18-0077-RS

Interpretive Summary: Plant-parasitic nematodes, microscopic roundworms that feed on the roots of plants, are production-limiting pests in most agricultural commodities grown in the Pacific Northwest (PNW) of the United States. To understand more about the distribution and presence of plant-parasitic nematodes in the PNW, data from five years were obtained from regional nematode diagnostic laboratories. These data were then analyzed to assess nematode trends across the region. It was found that 86% of soil samples processed by the diagnostic laboratories had at least one type of plant-parasitic nematode present. The most commonly found plant-parasitic nematodes was the root-lesion nematode while the pin nematode occurred at the highest maximum density. This report provides the first comprehensive assessment of the occurrence, distribution, and population densities of plant-parasitic nematodes in the PNW.

Technical Abstract: The Pacific Northwest (PNW) of the United States (Idaho, Oregon, and Washington) is a diverse agricultural production area with over 400 different commodities grown in the region. Plant-parasitic nematodes are a constraint to the production of many of these commodities. Soil sample data from 2012-2016 were obtained from nematode diagnostic laboratories in the region to assess trends in occurrence, population densities, and distribution of plant-parasitic nematodes in the PNW. A total of 38,022 unique data points were analyzed. Fifteen genera of plant-parasitic nematodes were identified by diagnostic laboratories, with 86% of the samples in the PNW containing at least one plant-parasitic nematode genus. The most commonly detected plant-parasitic nematode genus by diagnostic laboratories in the PNW was Pratylenchus, with a regional percentage occurrence of 69%. The next most commonly encountered genera were Tylenchorynchus, Meloidogyne, and Paratrichodorus with > 20% occurrence. Other nematode family/genera encountered in 2 to 17% of diagnostic samples included Paratylenchus, Helicotylenchus, Criconematidae, and Xiphinema. Paratylenchus had the highest maximum population density, 55,363 nematodes/250 cc soil, which was 2.5 times higher than the next highest maximum population density for Meloidogyne (21,760 nematodes/250 cc soil). Paratylenchus also had the highest mean population density when present in a sample with 462 nematodes/250 cc. The two most economically-important genera in the PNW, Pratylenchus and Meloidogyne, were considered at the species level by some laboratories. The number of plant-parasitic nematode samples processed in the PNW by diagnostic laboratories has significantly increased from 2012-2016. These laboratories provide a valuable service to agriculture in the PNW and also serve as a rich source of information on plant-parasitic nematode distribution, occurrence, and abundance, that when analyzed, provides an empirical basis upon which to interpret individual grower reports and make management recommendations.