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Geographical distribution and diversity of current plant species have been strongly shaped by climatic oscillations during the Quaternary. Analysing the resulting divergence among species and differentiation within species is crucial to understand the evolution of taxa like the Vitis genus, which provides very useful genetic resources for grapevine improvement and might reveal original recolonization patterns due to growth habit and dispersal mode. Here, we studied the genetic structure in natural populations of three species from eastern North America: Vitis aestivalis, V. cinerea and V. riparia using different marker types. Vitis aestivalis and V. cinerea showed higher diversity than V. riparia. The two former species are less differentiated, confirming an earlier divergence of V. riparia. V. aestivalis and V. riparia exhibited different genetic groups on both sides of the Appalachian Mountains that could mirror different recolonization routes from southern refugia. Genetic structure was stronger in V. cinerea, for which two varieties (var. berlandieri and var. cinerea) are morphologically recognized. Our results confirm this distinction and suggest the existence of three other lineages within var. cinerea. These discontinuities appear linked to adaptation of var. berlandieri to dry and limy areas of Texas and partially to the Mississippi River Valley. Rapid range expansions from refugia upon climate warming are also suggested by the low linkage disequilibrium values observed. Furthermore, large variation for downy mildew resistance was observed in the three species. Our findings appeared consistent with the vegetation history of eastern North America. [ABSTRACT FROM AUTHOR]

The most economically important diseases of grapevine cultivation worldwide are caused by the fungal pathogen powdery mildew ( Erysiphe necator syn. Uncinula necator) and the oomycete pathogen downy mildew ( Plasmopara viticola). Currently, grapegrowers rely heavily on the use of agrochemicals to minimize the potentially devastating impact of these pathogens on grape yield and quality. The wild North American grapevine species Muscadinia rotundifolia was recognized as early as 1889 to be resistant to both powdery and downy mildew. We have now mapped resistance to these two mildew pathogens in M. rotundifolia to a single locus on chromosome 12 that contains a family of seven TIR- NB- LRR genes. We further demonstrate that two highly homologous (86% amino acid identity) members of this gene family confer strong resistance to these unrelated pathogens following genetic transformation into susceptible Vitis vinifera winegrape cultivars. These two genes, designated resistance to U ncinula necator ( Mr RUN1) and resistance to P lasmopara viticola ( Mr RPV1) are the first resistance genes to be cloned from a grapevine species. Both Mr RUN1 and Mr RPV1 were found to confer resistance to multiple powdery and downy mildew isolates from France, North America and Australia; however, a single powdery mildew isolate collected from the south-eastern region of North America, to which M. rotundifolia is native, was capable of breaking Mr RUN1-mediated resistance. Comparisons of gene organization and coding sequences between M. rotundifolia and the cultivated grapevine V. vinifera at the Mr RUN1/ Mr RPV1 locus revealed a high level of synteny, suggesting that the TIR- NB- LRR genes at this locus share a common ancestor. [ABSTRACT FROM AUTHOR]

Downy mildew of grape caused by Plasmopara viticola 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 P. viticola samples from Vitis vinifera 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 P. viticola species complex 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 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. P. viticola clade aestivalis 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.