Fusarium poae and Fusarium crookwellense, Fungi Responsible for the Natural Occurrence of Nivalenol in Hokkaido.

To determine the reasons for the natural occurrence of nivalenol in the northernmost area of Japan, scabby wheat was harvested from 19 crop fields in Hokkaido. Mycological surveys and analysis for mycotoxin contamination were performed. Among 13 wheat grain samples harvested in seven locations, 9, 2, and 6 samples were positive for deoxynivalenol, nivalenol, and zearalenone, respectively, at levels ranging from 0.03 to 1.28 mug/g, 0.04 to 1.22 mug/g, and 2 to 25 ng/g, respectively. The predominant Fusarium species of the scabby wheat examined were F. sporotrichioides, F. avenaceum, F. poae, and F. crookwellense. Fifteen of 48 F. poae isolates and all four F. crookwellense isolates were screened for the production of seven derivatives of trichothecenes and zearalenone respectively, on rice culture. One isolate of F. poae produced diacetoxyscirpenol alone (4.3 mug/g); seven produced nivalenol (1.3 to 23.8 mug/g), 4-acetylnivalenol (0.1 to 4.6 mug/g), and diacetoxyscirpenol (0.9 to 99.5 mug/g); and five produced nivalenol alone (0.4 to 3.5 mug/g). The remaining two isolates produced no trichothecenes. Zearalenone production was not found in any isolate of F. poae tested. All isolates of F. crookwellense produced nivalenol (0.9 to 22.5 mug/g), 4-acetylnivalenol (0.5 to 25.0 mug/g), and zearalenone (1.4 to 162.5 mug/g). From these results, it is apparent that deoxynivalenol and zearalenone, and occasionally nivalenol, occur naturally throughout Hokkaido, and it is suggested that nivalenol-producing F. poae and F. crookwellense strains are responsible for the natural contamination with nivalenol found in the northernmost area of Japan. Furthermore, it was found for the first time that several isolates of F. poae distributed in Hokkaido possessed the ability to produce both type A and type B trichothecenes.