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Population genomics reveals high mutation rate and divergence among populations of blueberry pathogen Exobasidium maculosum

Annakay Abrahams: University of Georgia

<div><em>Exobasidium maculosum</em> is an emerging pathogen of blueberry (<em>Vaccinium</em> spp.) with increasing prevalence in the southeastern United States. The fungus causes Exobasidium leaf and fruit spot and has the potential to cause significant economic loss. Our goal is to identify the genetic basis of high levels of diversity seen among populations of <em>E. maculosum.</em> The mutation rate of <em>E. maculosum</em> was calculated using a fluctuation assay that measures the number of spontaneously arising mutants on selective media. Additionally, 15 isolates of <em>E. maculosum </em>equally representing the three distinct previously identified populations of Georgia and North Carolina in the southeastern United States and a population from northeastern North America represented by isolates from Maine and Nova Scotia, Canada, were sequenced and investigated for genes involved in rapid divergence and DNA repair pathways. Our results suggest that populations of <em>E. maculosum</em> are divergent, especially near the <em>RAD21</em> gene, which is involved in DNA repair of double strand breaks. Additionally, results of the fluctuation assay and genomic analyses suggest that the elevated diversity in the pathogen results from a high mutation rate. Pathogens with an increased mutation rate have the ability to adapt quickly giving them a selective advantage in host invasion and manipulation. Gaining insight into the evolution of <em>E. maculosum </em>is beneficial for disease management and understanding disease emergence.</div>