|Abstract or Summary
- A major constraint to the production of self-rooted wine grapes (Vitis vinifera) in eastern Washington is plant-parasitic nematodes. Plant-parasitic nematodes can impact grape productivity by limiting water and nutrient uptake, educing physiological changes, and extracting plant nutrients from roots, thereby reducing root biomass, plant vigor, and yield. The most commonly encountered plant-parasitic nematodes in Washington V. vinifera vineyards are Meloidogyne hapla, Mesocriconema xenoplax, Pratylenchus spp., Xiphinema americanum, and Paratylenchus sp.; however, little is known about their biology, distribution, and pathogenicity in this production system. Therefore, the objectives of this study were to 1) determine the spatial distribution of plant-parasitic nematodes in eastern Washington V. vinifera vineyards, and 2) determine the host status of V. vinifera varieties and clones predominantly grown in Washington, and several Vitis spp. rootstocks to M. hapla. For the first objective, two vineyards in eastern Washington were sampled over a two-year period to determine the horizontal and vertical distribution of plant-parasitic nematodes. To achieve the second objective, V. vinifera varieties and clones and Vitis spp. rootstocks were inoculated with M. hapla, grown in the greenhouse, and destructively harvested to determine nematode reproduction. Results from the spatial studies showed that, in general, populations of M. hapla and M. xenoplax were aggregated under irrigation emitters and that population densities of these nematodes decreased with soil depth. While Pratylenchus spp. population densities also decreased with depth, populations of these nematodes were concentrated along the alley ways between vine rows. Paratylenchus sp. and X. americanum were random in both their vertical and horizontal distributions within the vineyards. We also found that soil moisture plays a dominant role in the distribution of fine roots and plant-parasitic nematodes within semi-arid vineyards. Where soil moisture was the highest, fine root biomass and population densities of M. hapla and M. xenoplax were also the highest. The opposite was true for Pratylenchus spp., with higher population densities of this nematode in drier areas of the vineyard. There was no relationship of X. americanum and Paratylenchus sp. population densities with soil moisture. These results show there is potential to only treat a 60 cm area around the vine row when targeting M. hapla and M. xenoplax; however, this strategy would not be effective against X. americanum or Paratylenchus sp. It also appears that Pratylenchus spp. are not parasites of V. vinifera in this production system and that there may not be a need to consider these nematodes from a management perspective. In our host status trials with M. hapla, all of the V. vinifera varieties and clones were excellent hosts for M. hapla, but the magnitude of increase in population size of M. hapla on white (Chardonnay and Riesling) compared to red (Cabernet Sauvignon, Merlot, and Syrah) varieties was significantly greater. White varieties had higher M. hapla eggs/g root and an almost 40% higher reproduction factor value than red varieties. All the Vitis spp. rootstocks screened (Salt Creek, Freedom, Harmony, St. George, Riparia Gloire, 101-14, 3309C, 110R, and 420A) allowed very little or no M. hapla reproduction, and therefore are considered non-hosts. This research will provide Washington grape growers with the knowledge to select appropriate planting material to minimize the impact of M. hapla on grapevines. The results of both studies greatly expand the knowledge of the spatial distribution of plant-parasitic nematodes in semi-arid Washington V. vinifera vineyards as well as the host status of commonly planted V. vinifera varieties to M. hapla.