Genetic diversity of Sclerotinia species from Alaskan vegetable crops

White mold diseases are prevalent and difficult to manage on vegetable crops in the Matanuska Valley, the main agricultural region of Alaska. Prior research on Sclerotinia sclerotiorum, the primary white mold pathogen throughout the world, has shown it to be predominantly clonal in cool temperate regions, whereas sexual recombination contributes to the population structure in milder climates. We examined the population structure of the fungus in the subarctic region of Alaska to determine whether the trend towards clonality is sustained at more extreme latitudes. Microsatellite and ribosomal DNA markers revealed that S. sclerotiorum populations in Alaska comprise predominantly, if not exclusively, nonrecombining clonal lineages. Surprisingly, many diseased plants were found to be infected by the cryptic Sclerotinia sp. 1, a closely related fungus previously reported on wild plant species and cultivated potato from Norway. In some fields, Sclerotinia sp. 1 was the only pathogen involved in disease. However...