Growth Responses of Potted Vitis vinifera Cultivars Differ to a Mycorrhizal Inoculant and Phosphorus Fertilizer

Biological amendments, such as arbuscular mycorrhizal (AM) fungal inoculant products, are increasingly incorporated into agricultural management plans as a way to improve plant productivity. However, the effects of mycorrhizal inoculants on plant growth are context-dependent and can vary with soil fertility and among plant cultivars. To optimize the use of mycorrhizal inoculant products on wine grapes at the nursery stage, we tested the effect of a mycorrhizal inoculant product with and without the addition of phosphorus (P) fertilizer on the growth and tissue nutrients of two popular Vitis vinifera cultivars, Merlot and Chardonnay. We rooted dormant cuttings in the following respective treatments: no AM fungal inocula or P fertilizer; AM fungal inocula; P fertilizer; and coamendment of AM fungal inocula and P fertilizer. We grew the grapevines in pots for 5 months in a greenhouse. Growth responses to treatments differed between cultivars. 'Merlot' vines had a stronger growth response to the mycorrhizal inoculant product than 'Chardonnay', especially when no P fertilizer was added. The co-amendment of AM fungi and P fertilizer resulted in larger root biomass for 'Merlot', but there was no effect of any treatment on the root biomass of 'Chardonnay'. 'Merlot' vines grown with the AM fungal inoculant product also had higher tissue P than uninoculated vines, but there was no effect of inoculation on tissue nutrients of 'Chardonnay'. This study provides evidence of grapevine cultivar-specific responses to an AM fungal inoculant product in a greenhouse, which may be useful when planning nursery management strategies for the incorporation of biological amendments into grapevine production.