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An international perspective on genetic structure and gene flow in Cercospora beticola populations

Noel Knight: Cornell University, Plant Pathology & Plant-Microbe Biology Section

<div>Cercospora leaf spot, caused by the fungus <em>Cercospora beticola</em> Sacc., is an important disease of <em>Beta vulgaris</em> L. (table beet, sugar beet, and Swiss chard) worldwide. Disease impacts include reductions in commodity grading, and quantity and quality of extractable sugars from sugar beet roots. Conidia of <em>C. beticola</em> disperse locally by water or wind to initiate and expand disease foci in fields. Mechanisms for long distance pathogen dispersal and epidemic initiation are largely unknown. Studies of populations from Western Europe, Iran, New Zealand, Turkey, and the USA reported high levels of genetic diversity. Moreover, in some populations, equal ratios of two mating types suggests an active, and potentially mobile, teleomorph. In Europe, long distance dispersal of <em>C. beticola</em> is implied by evidence of high levels of gene flow between isolates across the region, resulting in a single panmictic population. Furthermore, recurrent clonal lineages shared between the USA and Europe provided evidence for intercontinental genotype flow. The genetic relationships among <em>C. beticola</em> isolates from nine countries (Canada (n=37), Chile (n=28), Denmark (n=9), England (n=9), Germany (n=10), Italy (n=11), Sweden (n=8), Turkey (n=7), and four states in the USA (n=1073)) were assessed using 12 microsatellite markers. This information will indicate the potential movement of <em>C. beticola </em>between regions and has implications for global disease management.</div>