Genetic diversity and aggressiveness of Fusarium virguliforme isolates across the Midwestern United States

Authors: OLARTE, RODRIGO - University Of Minnesota; HALL, REBECCA - University Of Minnesota; TABIMA, JAVIER - Clark University; MALVICK, DEAN - University Of Minnesota; Bushley, Kathryn

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/13/2021
Publication Date: 12/15/2021
Citation: Olarte, R.A., Hall, R., Tabima, J., Malvick, D., Bushley, K.E. 2021. Genetic diversity and aggressiveness of Fusarium virguliforme isolates across the Midwestern United States. Phytopathology. https://doi.org/10.1094/PHYTO-05-21-0191-R.
DOI: https://doi.org/10.1094/PHYTO-05-21-0191-R

Interpretive Summary: Fusarium virguliforme, the causal agent of soybean sudden death syndrome, has spread across the Midwestern US since its first detection in Arkansas. Despite differences observed in the virulence of this invasive pathogen, previous reports have not been able to identify genetic differences. Here, we examined genetic diversity and measured virulence of isolates along a south to north latitudinal gradient from the original point of detection of this pathogen in the U.S. in Arkansas to its northernmost distribution in Minnesota. Three genetically distinct groups were identified within the U.S. One group had lower genetic diversity and was restricted only to southern states, while the other two showed greater genetic diversity and have spread northward through most soybean production areas in the Midwest. However, we did not find any correlation between genetic groups and virulence, suggesting neutral genetic markers may not capture genetic variation responsible for virulence.

Technical Abstract: Sudden death syndrome (SDS) of soybean is a damaging disease caused by the fungus Fusarium virguliforme. Since this pathogen was first reported in the southern US state of Arkansas in 1971, it has spread throughout the Midwestern U.S. The SDS pathogen primarily colonizes roots but also produces toxins that translocate to and damage leaves. Previous studies have detected little to no genetic differentiation among isolates, suggesting F. virguliforme in North America has limited genetic diversity and a clonal population structure. Yet, isolates vary in virulence to roots and leaves. We characterized a set of F. virguliforme isolates from the Midwestern U.S. representing a south to north latitudinal gradient from Arkansas to Minnesota. Ten previously tested microsatellite loci were used to genotype isolates and plant assays were conducted to assess virulence. Three distinct population clusters were differentiated across isolates. Although isolates ranged in virulence classes from low to very high, little correlation was found between virulence phenotype and cluster membership. Similarly, population structure and geographic location were not highly correlated. However, the earliest diverging cluster (cluster 1) had the lowest genetic diversity and was detected only in southern states, while clusters 2 and 3 were distributed across the Midwest and were predominant in Minnesota. Cluster 2 had the greatest genetic diversity and was found along the northern edge of the known distribution. The results support three genetically distinct population clusters of F. virguliforme in the U.S., with clusters 2 and 3 contributing most to spread of this fungus across the Midwest.