Population genetic structure and cryptic species of Plasmopara viticola in Australia

Authors: TAYLOR, ANDREW - Murdoch University; Knaus, Brian; Grunwald, Niklaus - Nik; BURGESS, TREENA - Murdoch University

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/29/2019
Publication Date: 6/19/2019
Citation: Taylor, A.S., Knaus, B.J., Grunwald, N.J., Burgess, T. 2019. Population genetic structure and cryptic species of Plasmopara viticola in Australia. Phytopathology. 109(11):1975-1983. https://doi.org/10.1094/PHYTO-04-19-0146-R.
DOI: https://doi.org/10.1094/PHYTO-04-19-0146-R

Interpretive Summary: Downy mildew of grape, caused by the fungal organism Plasmopara viticola, has been a major disease affecting vineyards in Australia for over a century. However, the disease was not observed in commercial production areas of Western Australia until 1998. The source of the pathogen population in Western Australia remains unknown while the genetic diversity of the disease in other Australian states has rarely been investigated, in contrast to populations in the northern hemisphere. We characterized genetic diversity of populations of the pathogen in Western Australia. Representative samples from within Australia, Brazil and Uruguay were also genotyped. Our findings suggest the Australian and South American populations of the plant pathogen P. viticola are more closely related to the European population than the North American, 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. This work provides novel insights into the emergence of downy mildew disease in Australian vineyards.

Technical Abstract: Downy mildew of grape, caused by Plasmopara viticola, has been a major pathogen affecting vineyards in Australia for over a century. However, the disease was not observed in commercial production areas of Western Australia until 1998. The source of the P. viticola population in Western Australia remains unknown while the genetic diversity of the disease in other Australian states has rarely been investigated, in contrast to populations in the northern hemisphere. DNA was extracted from 381 P. viticola samples from Vitis vinifera and alternate hosts, collected via fresh and herbarium leaves from populations within Australia and FTA cards from North America, Brazil and Uruguay. A total of 32 DNA samples were provided from a French population. The populations were analysed genotyped using 16 polymorphic microsatellite markers. Representative samples from within Australia, Brazil and Uruguay were also genotyped to determine if any cryptic P. viticola populations were present. Our findings suggest the Australian and South American populations of P. viticola are more closely related to the European population than the North American, 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. P. viticola clade aestivalis was the only cryptic species detected in Australian and South American populations. Analysis of the Western Australian population suggests it is reproducing clonally, but further research is required to determine the mechanism as to how this is occurring.