Identification of micro satellite markers associated with downy mildew resistance in grape - An example of association mapping in perennial crops

Downy mildew is one of the most important diseases of grape, which affects the quality and productivity of grape production in India to a great extent. It is caused by the obligate fungal pathogen Plasmopara viticola and requires preventive and remedial spray of fungicides for management, which pose environment and health hazards besides increasing the cost of production. Development of downy mildew resistant commercial varieties is the top priority of grape breeders. The perennial and heterozygous nature of grapevines makes conventional approaches of resistance breeding laborious and time consuming. Marker assisted selection (MAS) offers an opportunity to these limitation. In MAS, a molecular marker closely linked to the trait is identified and used for the selection of the progenies. Microsatellites or SSR are highly reliable class of molecular markers. In this study, 15 Vitis specific SSR primers were used to amplify DNA from several resistant and susceptible grape accessions. One primer was monomorphic and 14 were polymorphic and detected 135 alleles with an average of 9.64. The number of alleles per primer ranged from 5 (VVMD28 and VVS16) to 16 (VVMD7). These accessions were also screened against the pathogen and were rated on a scale of 1-9. The disease rating was 1-3 for resistant accessions and 7-9 for susceptible accessions. Association mapping approach was applied for the analysis of marker and disease data. Eleven promising SSR markers showing significant association with disease resistance/susceptibility were identified. Six SSR markers showed promising association with resistance whereas five SSR marker bands were found to be associated with susceptibility. This work demonstrated the feasibility of association mapping for identification of linked marker in a perennial crop.