Pathogenic fungi associated with Fusarium foot rot of winter wheat in the semiarid Pacific northwest

Winter wheat plants and sail were collected from 288 nonirrigated fields in the semiarid Pacific Northwest during 1993 and 1994. Fungi associated with 5,390 crown and subcrown internodes from 10 Oregon and nine Washington counties were identified. Fusarium graminearum Group 1 was most widespread and the dominant pathogen associated with a crown and root rot named Fusarium foot rot or dryland root rot. F. culmorum was widely distributed in soil but was detected in plants in only half as many locations as F. graminearum. Other pathogens included Bipolaris sorokiniana, Microdochium nivale, and F. graminearum. Highly variable isolation frequencies for all five pathogens were presumed related to a very dry and a very wet survey year. Each pathogen was considered dominant or co-dominant at one or more sites during one or more years, All five species and F. acuminatum and F. oxysporum included isolates capable of killing wheat seedlings in the greenhouse.