Managing arbuscular mycorrhizal fungi in arid Columbia Basin vineyards of the Pacific Northwest United States

Authors: Schreiner, Roger - Paul; MOYER, MICHELLE - Washington State University; East, Katherine; Zasada, Inga

Submitted to: American Journal of Enology and Viticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/5/2023
Publication Date: 7/16/2023
Citation: Schreiner, R.P., Moyer, M.M., East, K.E., Zasada, I.A. 2023. Managing arbuscular mycorrhizal fungi in arid Columbia Basin vineyards of the Pacific Northwest United States. American Journal of Enology and Viticulture. 74(1). Article 074002. https://doi.org/10.5344/ajev.2023.23005.
DOI: https://doi.org/10.5344/ajev.2023.23005

Interpretive Summary: Root symbiotic fungi known as arbuscular mycorrhizal fungi (AMF) help grapevines obtain nutrients from soil and often increase drought tolerance, reduce negative impacts of pests or pathogens, and stabilize soil aggregates. Grape growers in the arid Columbia River basin region lack information regarding how to manage AMF, including knowledge of whether or not natural populations of AMF are sufficient to ensure healthy root colonization occurs in new plantings and what factors influence AMF in established plantings. By examining AMF root colonization along with soil and vine nutrient status in 32 wine grape vineyards of varying ages and in a seasonal study over two years in a vineyard with high populations of the northern root-knot nematode pest common in the region, we showed that root colonization by AMF was just as high in 1 to 2 year-old vineyards as in much older vineyards. Lower root colonization by AMF was most closely linked to high soil and plant nitrogen levels, and to high levels of the northern root-knot nematode. These results indicate that wine grape growers in the Columbia River basin region likely do not need to inoculate vines with AMF in new vineyard plantings, but should carefully manage nitrogen inputs and control the northern root-knot nematode in soils to maintain or enhance AMF in vineyards.

Technical Abstract: Background and Goals: Arbuscular mycorrhizal fungi (AMF) are root symbionts that help grapevines acquire nutrients from soil. Growers in many regions including the Columbia River basin of Oregon and Washington lack information needed to best manage AMF. Information lacking includes understanding if natural AMF populations are sufficient to ensure healthy colonization in new plantings, and what factors influence AMF in established plantings. Methods and Key Findings: AMF colonization of grapevine fine roots was determined in 32 commercial vineyards, and in a vineyard that was heavily infested by the northern root-knot nematode (NRKN, Meloidogyne hapla). Root colonization by AMF was as extensive in young vines (1 to 2 year-old) as in older vines (> 15 year-old) in the survey, and was high also throughout the season in the single vineyard trial. AMF colonization was greater in red cultivars compared to white, and in drip-irrigated compared to overhead-irrigated vineyards. AMF colonization was negatively correlated to soil nitrate and to leaf nitrogen (N) concentrations across vineyards, while arbsucules in roots were negatively correlated to NRKN populations in soil. Both AMF and arbuscules in roots were negatively correlated to NRKN populations per unit of fine root length at the beginning and end of the growing season in the heavily infested vineyard. Conclusions and Significance: Results suggest that AMF populations in soils of the Columbia River basin are ample to ensure high levels of grapevine root colonization, so inoculation is likely not needed when planting or replanting vineyards in the region. AMF colonization was reduced by high N and high populations of NRKN in soil.