Effects of an Arbuscular Mycorrhizal Fungus Inoculant and a Mycorrhizal Stimulant on Pink Root and Productivity of Dehydration Onion Crops Near Paterson, Washington

Researchers conducted field trials in 2016 near Paterson, Washington to evaluate whether commercial arbuscular mycorrhizal fungus (AMF) products could improve onion productivity or reduce pink root disease in dehydration onion crops. Two commercial products were tested: Mykos Liquid, an AMF inoculant containing Rhizophagus intraradices, and Myconate, a stimulant designed to promote native mycorrhizal associations in soil. Treatments were applied to coated onion seed and compared with untreated controls in replicated plots across two commercial, center-pivot irrigated fields. Fertilizer was also tested as a separate treatment to assess interactions with AMF products. Researchers measured plant stand counts, biomass, foliar nutrient concentrations, bulb yield and size, soluble solids (Brix), and pink root severity. Results showed limited effects from the AMF products under the nutrient-rich soil conditions present at the trial sites. Some treatments increased foliar sulfur and zinc concentrations and slightly increased bulb weight, but overall disease severity and yield differences were small. Fertilizer increased aboveground biomass and marketable bulb yield modestly.