Arbuscular Mycorrhizal Fungal Communities in Organic and Conventional Onion Crops in the Columbia Basin of the Pacific Northwest United States

This Phytobiomes Journal article compared arbuscular mycorrhizal fungal communities in organic and conventional onion fields in the Columbia Basin of Washington and Oregon, and also evaluated paired fumigated and nonfumigated conventional fields. AMF were detected in all fields and at all sampling times. Onion roots sampled midsummer had greater AMF colonization in organic than conventional fields, and fumigated conventional fields had lower colonization than nonfumigated fields. Pyrosequencing identified four AMF genera, with Glomus and Claroideoglomus dominating most samples. Organic fields supported greater AMF richness and diversity than conventional fields, especially in roots sampled directly from onion crops midsummer. However, the dominant AMF taxa were similar across management systems, and metam sodium fumigation did not consistently alter AMF community structure. Overall, the study found that organic and conventional production systems differed somewhat in AMF diversity, but common onion production practices in this region, including fumigation by chemigation, were not major drivers of the dominant AMF communities present in onion crops.