Species and Trichothecene Genotypes of Fusarium Head Blight Pathogens in Nebraska, USA in 2015-2016

Fusarium head blight (FHB) of wheat and other small grain cereals is a devastating and economically important disease caused by members of the Fusarium graminearum species complex (FGSC). FHB poses a threat to food security and food safety, due to yield and quality reduction, as well as mycotoxin contamination. To determine the diversity of species and trichothecene genotypes of the FGSC in Nebraska, 33 wheat samples were collected from FHB-affected fields during two consecutive years (2015 and 2016) and 50 Fusarium isolates were obtained from those wheat samples. Identification of F. graminearum was attempted by PCR using UBC85 and GO primers. However, these primers proved insufficient to accurately identify F. graminearum, because they were unable to discriminate between species within the FGSC. DNA was also subjected to a multilocus genotyping (MLGT) assay for the simultaneous determination of species identity. Inconclusive results from the MLGT assay prompted sequencing of the RED and TRI101 genes from four isolates. Sequence analysis identified two of the isolates as F. graminearum and the other two isolates as F. boothii. Additionally, intragenomic heterogeneity of their RED and TRI101 genes was detected. The trichothecene genotype of the Nebraska isolates was determined using a multiplex PCR assay. The overwhelming majority of isolates had the 15-ADON genotype. However, two isolates produced inconclusive results with the trichothecene genotyping multiplex PCRs. Under greenhouse conditions, these two isolates failed to cause disease and accumulate mycotoxins in the grain of the FHB-susceptible wheat cultivar Samson. This is the first study to report F. boothii isolates in Nebraska, as well as intrastrain RED and TRI101 sequence heterogeneity in FHB pathogens. The data obtained from this study can be used as baseline data for future surveillance studies in Nebraska and North America and to better understand the biology and ecology of FHB pathogens. The findings will also be useful to lessen the risk of mycotoxin contamination in wheat and wheat-based products. Advisor: Heather Hallen-Adam