Managing Arbuscular Mycorrhizal Fungi in Arid Columbia Basin Vineyards of the Pacific Northwest United States

Abstract

Background and goals Arbuscular mycorrhizal fungi (AMF) are root sym-bionts 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. Such lacking information includes understanding wheth-er 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 col onizati on of grapevi ne 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 col onizati on by AMF was as extensive i n young vines (one-to two-years-old) as in older vines (>15-years-old) examined in the survey, and was high throughout the season in the single vineyard trial. AMF colonization was greater overall in red wine grape cultivars than in white wine grape cultivars. AMF colonization correlated negatively with soil nitrate and leaf nitrogen (N) concentra-tions across vineyards, while arbuscules in roots correlated negatively with NRKN populations in soil. Both AMF and arbuscules in roots correlated negatively with 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.