Population Genetic Structure and Cryptic Species of in Australia.

Downy mildew of grape caused by is a global pathogen of economic importance to commercial viticulture. In contrast to populations in the northern hemisphere, few studies have investigated the population biology, genetic diversity, and origin of the pathogen in Australian production systems. DNA was extracted from 381 samples from and alternate hosts collected via fresh and herbarium leaves from populations within Australia and Whatman FTA cards from North America, Brazil, and Uruguay. A total of 32 DNA samples were provided from a French population. The populations were genotyped using 16 polymorphic microsatellite markers. Representative samples from within Australia, Brazil, and Uruguay were also genotyped to determine which of the cryptic species (clades) within the species complex were present. Our findings suggest the Australian and South American populations of are more closely related to the European population than the North American population, the reported source of origin of the pathogen. The Western Australian population had similarities to the South Australian population, and the tight clustering of samples suggests a single introduction into Western Australia. clade was the only clade detected in Australian and South American populations. Analysis of the Western Australian population suggests that it is reproducing clonally, but additional research is required to determine the mechanism as to how this is occurring.