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Title: First report of Fusarium wilt of alfalfa caused by Fusarium oxysporum f. sp. medicaginis in Wisconsin

Author
item PETERSON, JENNIFER - S&w Seed Company
item Samac, Deborah - Debby
item GRAU, CRAIG - University Of Wisconsin

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/10/2017
Publication Date: 1/22/2018
Citation: Peterson, J.J., Samac, D.A., Grau, C.R. 2018. First report of Fusarium wilt of alfalfa caused by Fusarium oxysporum f. sp. medicaginis in Wisconsin. Plant Disease. 102:447.

Interpretive Summary: Fusarium wilt disease of alfalfa occurs in alfalfa–growing areas around the world. Infection results in wilting of foliage followed by death of the stem. Reddish brown discoloration in the taproot is diagnostic for the disease. Plants with these symptoms were reported in Wisconsin for the first time in 2013-2016. The pathogen was isolated and identified using spore shape and size, diagnostic DNA sequences, and pathogenicity assays. Cultivars with resistance to Fusarium wilt are available and have been shown to have greater persistence and yield in areas where this pathogen is present. Information on the occurrence of this disease will enable producers to select the appropriate cultivars to obtain maximum yields and stand persistence.

Technical Abstract: Fusarium wilt, caused by Fusarium oxysporum f. sp. medicaginis, is an economically important vascular disease of alfalfa (Medicago sativa) throughout the world. Alfalfa plants with foliar wilt symptoms and reddish-brown arcs in roots consistent with Fusarium wilt were observed in disease assessment field plots in Columbia County, Wisconsin during the summers of 2013 to 2016. Roots of symptomatic plants were collected, dipped in 70% ethanol, flame sterilized, cut into thin slices, and incubated on potato dextrose agar medium amended with 0.05% streptomycin. Colonies of white mycelia with tan sporodochia producing macro- and microconidia morphologically similar to Fusarium spp. were observed after 3 weeks of incubation at room temperature. Six single spore isolates were characterized using spore morphology, diagnostic DNA sequences, and a pathogenicity assay. Taken together, the results suggest that F. oxysporum f. sp. medicaginis was isolated from the diseased alfalfa plants. This is the first report of F. oxysporum f. sp. medicaginis from alfalfa in Wisconsin, a major alfalfa producing state. Cultivars with resistance to Fusarium wilt are available and have been shown to have greater persistence and yield in areas where this pathogen is present.