Temporal dynamics and population genetic structure of Fusarium graminearum in the upper Midwestern United States

Authors: LIANG, JUNMIN - China Agricultural University; XAYAMONGKHON, HENRY - University Of Minnesota; Broz, Karen; DONG, YANHONG - University Of Minnesota; McCormick, Susan; ABRAMOVA, SVETLANA - Russian Institute Of Phytopathology; Ward, Todd; MA, Z - China Agricultural University; Kistler, Harold

Submitted to: Fungal Genetics and Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2014
Publication Date: 10/13/2014
Citation: Liang, J., Xayamongkhon, H., Broz, K.L., Dong, Y., McCormick, S.P., Abramova, S., Ward, T.J., Ma, Z.H., Kistler, H.C. 2014. Temporal dynamics and population genetic structure of Fusarium graminearum in the upper Midwestern United States. Fungal Genetics and Biology. 73:83-92.

Interpretive Summary: Fusarium head blight (FHB) disease is a major threat to the profitable and dependable production of wheat and barley crops in the United States. Development of disease resistance to FHB in wheat and barley requires accurate knowledge of the pathogenic fungus as it exists in farmer's fields and how it may change over time. In this paper we follow changes in the pathogen population from 1999 to 2013 in the midwestern United States. Major shifts in the pathogen population have taken place over this time period indicating that wheat and barley breeding programs must remain vigulence in order to account for newly emergent strains of the pathogenic fungus. Research descibed in this publication will be used by other plant scientists to improve disease management strategies in small grain crops. This goal can be achieved by the judicious deployment of resistant varieties or by manipulation of cultural practices to shift the balance in favor of plant health.

Technical Abstract: Fusarium graminearum sensu stricto causes Fusarium head blight (FHB) in wheat and barley, and contaminates grains with several trichothecene mycotoxins, causing destructive yield losses and economic impact in the United States. Recently, a F. graminearum strain collected from Minnesota (MN) was determined to produce a novel trichothecene toxin, called NX-2. In order to determine the spatial and temporal dynamics of NX-2 producing strains in MN, North Dakota (ND) and South Dakota (SD), a total of 463 F. graminearum strains were collected from three sampling periods, 1999-2000, 2006-2007 and 2011-2013. A PCR-RFLP based diagnostic test was developed and validated for NX-2 producing strains based on polymorphisms in the Tri1 gene. Trichothecene biosynthesis gene (Tri gene)-based polymerase chain reaction (PCR) assays and ten PCR- restriction fragment length polymorphism (RFLP) markers were used to genotype all strains. NX-2 strains were detected in each sampling period but with a very low overall frequency (2.8%) and were mainly collected near the borders of MN, ND and SD. Strains with the 3ADON chemotype were relatively infrequent in 1999-2000 (4.5%) but increased to 29.4% in 2006-2007 and 17.2% in 2011-2013. The distribution of 3ADON producing strains also expanded from a few border counties between ND and MN in 1999-2000, southward toward the border between SD and MN in 2006-2007 and westward in 2011-2013. Genetic differentiation between 2006-2007 and 2011-2013 populations (3%) was much lower than that between 1999-2000 and 2006-2007 (22%) or 1999-2000 and 2011-2013 (20%) suggesting that most change to population genetic structure of F. graminearum occurred between 1999-2000 and 2006-2007. This change was associated with the emergence of a new population consisting largely of individuals with a 3ADON chemotype. A Bayesian clustering analysis suggested that NX-2 chemotype strains are part of a previously described Upper Midwestern population. However, these analyses also suggest that the NX-2 isolates could represent a distinct population, but that interpretations of population assignment are influenced by the small number of NX-2 strains available for analysis.