Candidate Gene Approach to Identify Genes Underlying Quantitative Traits and Develop Diagnostic Markers in Potato

Potatoes (Solanum tuberosum L.) and humans (Homo sapiens L.) are both outcrossing species. The phenotypic variation of both is controlled by environnemental factors and by natural DNA polymorphisms between individuals. Therefore we adopt similar approaches as used in human population genetics, such as association mapping, to identify loci and their alleles that are causal for complex agronomic characters such as quantitative resistance to pathogens or tuber sugar content. Fonctional analysis of genes operating in resistance to pests and pathogens or in carbohydrate metabolism, either in potato itself or in other plants including the model species Arabidopsis thaliana (L). Heynh, provides many functional candidates for these complex agronomic traits. In our approach, fonctional candidate genes are tested for linkage to quantitative trait locl (QTL) for pathogen resistance or tuber quality traits, thereby selecting positional candidates (genes colocalizing with a QTL). DNA polymorphisme in or physically linked to positional candidate genes are then evaluated in populations of tetraploid potato genotypes and tested for association with phenotypes evaluated in the same populations. We have used the candidate gene approach to identify DNA-based markers that are diagnostic for quantitative resistane in late blight caused by Phytophthora infestans (Mont) de Bary, to the root cyst nematode Globodera pallida (Stone), and for chip color in tetraploid potato cultivars and in advanced breeding clones.