White Rot of Garlic and Onion (Causal Agent, Sclerotium cepivorum ): A Status Report from the Pacific Northwest

There is evidence from literature, state department of agriculture documents, and recent diagnoses that Sclerotium cepivorum, causal agent of white rot of garlic and onion, is spreading and/or becoming more established in the Pacific Northwest. Previously documented distributions are summarized and the fungus is reported for the first time from Latah Co., ID; Pend Oreille Co., WA; and Lake, Sanders, and Missoula counties, MT. Although known from a tightly quarantined prior occurrence in the Idaho portion of Treasure Valley (southwest Idaho), the pathogen has not been formally reported from that state nor from the state of Montana. Latah Co. has commercial production of seed garlic and borders adjacent Whitman Co., WA, where the National Plant Germplasm System (NPGS) maintains North America's largest non-commercial collection of garlic and wild/ornamental onion. Strict phytosanitary protocols have been implemented on the NPGS farm. Various areas within the Pacific Northwest have long been important for commercial Allium production, and a list of state departments of agriculture regulations addressing white rot is presented for Idaho, Oregon, and Washington. Accepted for publication 18 February 2013. Published 19 June 2013. This review presents a synopsis of published prior occurrences and distribution of white rot of garlic and onion in the Pacific Northwest, some recent novel records, regulations of various state departments of agriculture, and briefly comments on various challenges and prospects for successful management. Although diagnosis of the agent via symptoms and characteristic sclerotia is relatively reliable, morphologically similar, closely related species exist, so the authors also present a protocol for identification via ITS sequence analysis.