Effects of Three Arbuscular Mycorrhizal Fungi Inoculants on Pink Root and Yield in an Onion Crop Near Othello, Washington

Researchers evaluated three commercial arbuscular mycorrhizal fungi (AMF) inoculants in a commercial onion bulb field near Othello, Washington in 2017. The study tested whether AMF products could improve nutrient uptake, crop productivity, or resistance to pink root disease in intensive onion production systems in the Columbia Basin. Three products—AGTIV Specialty Crops Powder, MycoApply Ultrafine Granular, and Mykos Gold Granular—were applied to onion seed at planting and compared with a non-inoculated control in a randomized complete block design. Researchers measured stand counts, plant growth, bulb yield, bulb size distribution, and pink root severity. Most onion characteristics were similar across treatments, with no evidence that the AMF inoculants improved onion growth or reduced disease severity. Only the number and weight of medium-sized bulbs differed significantly, with fewer medium bulbs produced in plots treated with two of the AMF products compared to the control. Overall, results indicated no production benefit from applying these AMF inoculants under the management practices used in this commercial onion field.