COS 47-2 - An evaluation of mycorrhizal inoculants on the growth and foliar nutrient content of European wine grapes (Vitis vinifera) grown in live field soil

Abstract: Contemporary agricultural practices can reduce populations of arbuscular mycorrhizal (AM) fungi in the soil. AM fungi form a symbiosis with many land plants, aiding access to water and nutrients for the plant through a root-hyphal relationship. Given the benefits provided by these fungi, mycorrhizal inoculant products have been incorporated for use in agroecosystems, including vineyards. However, the efficacy of mycorrhizal inoculants on the growth and nutrient content of wine grapes warrants further investigation, especially when inoculants are added to soil with a resident microbial community already in place. Through a greenhouse study, we evaluated the effect of five different mycorrhizal inoculants on the growth, foliar nutrient content, and mycorrhizal colonization levels in roots of a popular, own-rooted European wine grape cultivar (Vitis vinifera, ‘Merlot’) when applied at two different rates of application. Young grapevines were grown for 120 days in 4L pots filled with live background field soil, representative of a new vineyard. Each experimental pot included a layer of 1) one of three mycorrhizal inoculant products, 2) a local soil inoculant collected from the rhizosphere of a native perennial shrub (Artemesia tridentata), or 3) a local soil inoculant collected from the rhizosphere of wine grapes in a 50-year-old vineyard. Plant growth measurements were taken every 30 days for the duration of the experiment and final plant biomass, percent root colonization by AM fungi, and foliar nutrient content were recorded at harvest.

Preliminary results suggest no differences in grapevine biomass or shoot length among inoculant types or application rates when grown in live field soil. Though foliar nutrient content of vines grown with a mycorrhizal inoculant showed differences from vines grown without inoculation, the initial nutrient content of each inoculant also varied. These results show that mycorrhizal inoculants, commercial or local, may not significantly improve vine growth or foliar nutrient content of young grapevines when planting in previously unmanaged field soil. Data on AM fungal colonization are still being collected and may provide further insight into the existing AM fungal inoculation potential found in unmanaged soil. Understanding how different mycorrhizal inoculants influence the growth, nutrient content, and root colonization of newly planted crops will help to inform management strategies aimed at optimizing the use of biological amendments in agroecosystems.