First report of scab on cultivated wild rice in Minnesota

Fusarium spp. were isolated from seed of cultivated wild rice (Zizania palustris L.) that was dried to 20-21% moisture content following the 1993 growing season. Fusarium graminearum Schwabe was isolated most frequently, but F. culmorum (Wm. G. Sm.) Sacc., F. moniliforme J. Sheld., F. sporotrichoides Sherb., and F. subglutinans (Wollenweb. & Reinking) P. E Nelson, T. A. Toussoun, & Marasas also were isolated. Fusarium spp. were not isolated from seed stored in water immediately after harvest, the normal procedure to store seed for sowing the following year. Scab has not been reported on cultivated wild rice. Therefore, during the 1994 growing season, plants in the field were observed at four different locations approximately every 10 days, beginning at anthesis, for symptoms of infection by Fusarium spp. We observed spikelets that were bleached to a tan color and were either sterile or contained shriveled and discolored seed. Frequently a pink to orange discoloration caused by sporodochia containing conidia, conidiophores, and mycelium was observed during high humidity conditions. Fusarium graminearum was isolated from 100% of spikelets and seed displaying these symptoms. Other Fusarium spp. were not isolated from symptomatic seed in 1994. Conditions for the cultivation of wild rice, especially high humidity, are optimum for scab development. To our knowledge this is the first report of scab on cultivated wild rice. Cultivated wild rice is now becoming widely used in rice mixtures and other foodstuffs throughout the United States. Therefore, this represents another mode by which harmful toxins that may potentially be produced by Fusarium spp. are introduced into the human food chain.