Population subdivision of Fusarium graminearum from barley and wheat in the upper Midwestern United States at the turn of the century

Authors: LIANG, JUNMIN - China Agricultural University; LOFGREN, LOTUS - University Of Minnesota; MA, ZHANHONG - China Agricultural University; Ward, Todd; Kistler, Harold

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/19/2015
Publication Date: 11/15/2015
Publication URL: http://handle.nal.usda.gov/10113/62335
Citation: Liang, J., Lofgren, L., Ma, Z., Ward, T.J., Kistler, H.C. 2015. Population subdivision of Fusarium graminearum from barley and wheat in the upper Midwestern United States at the turn of the century. Phytopathology. 105(11):1466-1474.

Interpretive Summary: Fusarium graminearum is a fungus that causes Fusarium head blight (FHB) in wheat and barley, and contaminates grain with mycotoxins such as deoxynivalenol (DON) that pose a significant threat to food safety and animal health. Recent studies of genetic variation identified two distinct populations of FHB pathogens from wheat and indicated that a recently introduced FHB population was spreading rapidly in major wheat growing regions of North America. However, a recent study reported only a single population of these pathogens on barley suggesting that pathogen populations on barley were different from wheat. In the current research, we demonstrated that both of the FHB pathogen populations described from wheat, were also causing FHB of barley in the Upper Midwest of the United States. However, the results also indicated that the recently introduced population was more prevalent on wheat than on barley and that the introduced population was most common in northern parts of Upper Midwest. The introduced population on wheat and barley had a high proportion of isolates with the novel 3ADON toxin type. However, the novel NX-2 toxin type, which was previously observed at low frequency on wheat, was not observed among the barley isolates in this collection. The results reported in the current study clarify the geographic and host distribution of FHB pathogen diversity in the Upper Midwest, providing important information for FHB and mycotoxin testing and control programs.

Technical Abstract: Fusarium graminearum, the causal agent of Fusarium head blight (FHB) in wheat and barley, is one of the most economically destructive pathogens of these grains worldwide. Recent population genetic studies of the pathogen obtained from wheat in North America supported population subdivision in part correlated with the spectrum of trichothecene mycotoxins produced ("chemotype") for individuals within each population. In contrast, a recent study of F. graminearum obtained from diseased barley in the upper Midwestern United States concluded that only a single population was present, consisting of individuals with various chemotypes. To test whether strains derived from different hosts potentially have different population dynamics, we obtained the barley strains used in the previous study and compared them to wheat strains isolated at a similar time and geographic origin. A total of 247 F. graminearum isolates from barley were assigned firmly into two clusters by a Bayesian clustering method. Subdivision within the barley population corresponded to the previously described NA1 (correlated with the 15ADON chemotype) and NA2 (correlated with the 3ADON chemotype) populations from wheat. However, the barley population exhibited a higher level of genetic differentiation between NA1 and NA2 populations in both new and old sampling periods, fewer admixed individuals and evidence of unidirectional gene introgression (15ADON strains with NA2 genetic backgrounds). The results suggest less recombination between NA1 and NA2 populations on barley compared to wheat. The frequency of 3ADON chemotype strains in the most recent barley population suggests a latitudinal cline from the northern (49%), central (40%) to the southern (29%) sampling area. The potential to produce a novel trichothecene, 3a-acetoxy, 7a, 15-dihydroxy-12, 13-epoxytrichothe-9-ene (NX-2), was not detected in the barley population but occurred at a low rate (2.4%) in the wheat population.