Arbuscular Mycorrhizal Fungi: Worth all the hyphae?

By Wynne Reichheld, Tender Fruit and Grape Research Assistant and Kathryn Carter, Fruit Specialist (Tender fruit and Grape)

What are Abruscular Mycorrizal fungi (AMF)?

Fungi are well known as decomposers, with common representatives including yeasts and moulds, though this kingdom’s most recognizable group is mushrooms. Many fungi are also well known as pathogens, with over 5000 known species that parasitize economically significant plants including Erysiphe spp., the fungus that causes powdery mildew. Fortunately, there are also many species of fungus that form beneficial relationships with plants. Arbuscular mycorrhizal fungi, or AMF, play an important role in nutrient uptake and the ability of vines to withstand stress from drought, disease and insects. AMF are composed of hyphae: tightly packed filaments that surround and penetrate the roots of certain plants. Depending on the species of fungus, the hyphae will either form arbuscules that aid in nutrient exchange, or hyphal coils which increase the functional root area.

Research on AMF in grapes in New York

Over the last twenty years, the benefits of AMF use in vineyards have been studied in France, Italy, and Greece using commercially available inoculants. Unfortunately there has been little research done on these products in North America until it was recently investigated at Cornell University in New York state (Vanden Heuvel et al., 2020). Although there are currently several AMF products commercially available, Cornell research focused on Glomus based treatments as they have been proven in other crops to have a positive impact on mycorrhizal associations.

Dr. Vanden Heuvel tested Big Foot Concentrate, BioOrganics LLC, MycoGrow® Soluble, MycoApply Endo granular, and MycoApply all Purpose granular in greenhouse and commercial vineyards.  Similarly to the European studies, the Vanden Heuvel lab found that vines inoculated with AMF products had increased root growth, causing improved nutrient uptake in nutrient-poor soils, especially those lacking phosphorus and potassium. All of the AMF treatments increased the number of vesicles, arbuscules, and hyphae found on the roots of vines. Vines treated with AMF also showed a sizeable increase in the concentration of macro and micronutrients (N was 0.77% in the leaves of AMF inoculated vines, but only 0.62% in the leaves of the non-inoculated vines).  After five months of growth, the inoculation products tested (BioOrganics and MycoApply) had resulted in 2x the root growth as the control. Mycoapply all purpose granular resulted in a sizeable increase in root diameter, while all three AMF treatments increased root length.

Evaluating AMF in Ontario

In 2020, OMAFRA worked with a grower collaborator to initiate a trial evaluating the impact treating young vines with AMF prior to planting. The trial included four treatments: untreated control, Stella Maris (Ascophyllum nodosum, or kelp), Biocult (AMF) and MycoApply (AMF). Prior to planting, young vines were dipped in (Mycoapply Super Con 10 (10 g/ 4 hectares), and Biocult (200 g / 1200 plants) in 31 gallon pails. For Stella Maris treatments, vines were left to soak for 24 hours in 3.5 mL of product/L of water prior to planting. Throughout the summer vine growth was measured on 2 shoots on 6 vines in each treatment. Mean shoot length at several points in the growing season is shown on the graph in Figure 1.

The shoots of control vines were significantly shorter than those that were treated with AMF (Biocult, Mycoapply) and Stella Maris (kelp). There was also a significant increase in growth of vines colonized using Biocult and Mycoapply Endo compared to vines that were treated with Stella Maris (kelp) (Table 1). There were no significant differences in shoot growth between vines treated with Biocult and Mycoapply in 2020.

Preliminary data that we have collected suggests that in the use of AMF products has a positive impact on vine growth, which may be of benefit to growers looking at establishing vineyards in some sites, especially those with low phosphorous and low potassium. However, more information is needed to evaluate the costs and benefits of using these products in commercial vineyards.

This summer OMAFRA is continuing to conduct research on the use of AMF in vineyards. Stay tuned for more information.

Resources

• Arbuscular mycorrhiza symbiosis in viticulture: a review
• Biocult
• Drought responses of arbuscular mycorrhizal grapevines
• Effects of drought stress on mycorrhizal and non-mycorrhizal Cabernet Sauvignon grapevine grafted onto various rootstocks
• Enhancing Vine Health with Commercial Arbuscular Mycorrhizal Inoculants (Vander Hoeven, 2020)
• Mycoapply
• Stella Maris