Linkage disequilibrium in wild French grapevine, Vitis vinifera L. subsp. silvestris.

Association mapping based on linkage disequilibrium (LD) can provide high resolution for whole-genome mapping of genes underlying phenotypic variation. This field has received considerable attention over the last decade. We present here the first characterization of LD in wild French grapevine, Vitis vinifera L. subsp. silvestris. To assess the pattern and extent of LD, we used a sample of 85 plants from southern France and 36 microsatellite markers distributed over 5 linkage groups. LD was evaluated with independence tests and multiallelic r(2), using both unphased genotypic data and reconstructed haplotypic data. LD decayed rapidly, with r(2) values decreasing to 0.1 within 2.7 cM for genotypic data and within 1.4 cM for haplotypic data. Compared to the results of a previous study on cultivated grapevine subsp. sativa, where significant LD was found up to 16.8 cM, LD in subsp. silvestris was no longer significant past 1.4 cM. LD was therefore 12 times further extended in cultivated than wild grapevine, even though LD in wild grapevine seemed to extend slightly further than in wild relatives of other crops. Domestication bottlenecks and vegetative propagation are the primary factors responsible for this difference between cultivated and wild grapevine. The rapid decay of LD observed in this study seems promising for future association mapping studies of functional variation in wild V. vinifera grapevine.