[Synopsis] Virulence to wheat heads of 12 Fusarium species isolated from kernels and scabby heads of wheat and barley was tested. F. graminearum, F. avenaceum, F. culmorum, F. nivale (Microdochium nivale), F. acuminatum and F. sporotrichioides caused scab symptoms on wheat heads. F. graminearum was most prevalent and distributed all over Japan, whereas F. nivale was predominant in Hokkaido of northern Japan. Pathogenicity of F. graminearum to wheat heads was strongest. All virulent fusaria caused discoloration of wheat grains, and induced seedling blight by spray, seed and soil-inoculation. Spores of F. graminearum dispersed mainly at night and the number of the dispersed spores was affected with the wet time per day. Virulent fusaria to wheat heads were recovered from wheat and barley field soil and plant refuse in the soil. All of the scab pathogens except for F. nivale could survive during summer and overwinter in wheat heads in soil. Conidia of F. culmorum, F. acuminatum and F. acuminatum could survive more than 150 days in soil. Wheat and barley scab caused by F. nivale was recognized in central Japan with no snow cover in winter. The disease cycle of causal fusaria on wheat and barley in Japan was presumed by the results
