Identification, aggressiveness and mycotoxin production of \u3ci\u3eFusarium graminearum\u3c/i\u3e and \u3ci\u3eF. boothii\u3c/i\u3e isolates causing Fusarium head blight of wheat in Nebraska

Fusarium head blight (FHB) is an economically important disease caused by several Fusarium species affecting wheat. Besides causing significant yield losses, infected grain may be contaminated with mycotoxins, primarily trichothecenes, that are harmful to both humans and animals. In recent years, reports of shifts in FHB pathogen populations in North America have highlighted the need for increased vigilance. This dissertation describes a four-year survey evaluating the species, trichothecene genotype and phenotypic diversity of FHB pathogens infecting Nebraska wheat. Most of the isolates were identified as F. graminearum (n=67). Additional species included F. boothii (n=3), F. poae (n=2) and F. acuminatum (n=1). An F. graminearum x F. boothii interspecific hybrid was also identified. All F. graminearum and F. boothii isolates had the 15-ADON genotype, which is the only genotype that has been reported in the state. Since F. boothii had not been previously reported from wheat in the U.S., spikes of the susceptible wheat cultivar Wheaton were inoculated with F. boothii isolates from Nebraska under greenhouse conditions in order to fulfill Koch’s postulates. FHB symptoms developed in plants inoculated with F. boothii, and F. boothii was re-isolated from symptomatic plants. A larger greenhouse study was performed to compare the aggressiveness and DON production in wheat among 13 F. graminearum and all three F. boothii isolates from Nebraska. Isolates of F. graminearum were more aggressive and produced more DON than F. boothii isolates. Since most FHB pathogens are indistinguishable morphologically and culturally, a simple PCR-based assay was developed to identify FHB pathogens in order to facilitate species surveillance. Primers were designed based on polymorphisms in the trichothecene 3-O-acetyltransferase (TRI101) gene. Individual reactions have been developed to differentiate F. graminearum, F. boothii, F. asiaticum, F. gerlachii, and F. culmorum from related species, as well as a multiplex reaction to target these five species simultaneously. The research described here expands knowledge of the diversity of FHB pathogens in Nebraska, which will be useful for disease management and provide a baseline for future FHB surveys. The PCR assay described here is expected to facilitate pathogen surveillance. Advisors: Heather E. Hallen-Adams and Stephen N. Wegul