Some examples of the benefits and limitations of marker-assisted selection in potatoes

Marker-assisted selection (MAS) is only possible if the molecular markers are easy to use and informative. In the potato, a tetraploid and heterozygous species, MAS is still relatively underdeveloped at present. Our approach was, on the one hand, to identify molecular markers linked to traits of interest from segregating diploid populations and to test their transferability to the tetraploid level and, on the other hand, to test molecular markers already published in different tetraploid gene pools. The traits selected were resistance to pests and diseases (leaf blight caused by Phytophthora infestans, resistance to the cyst nematodes Globodera rostochiensis and G. pallida, and resistance to the Y virus) and the glycoalkaloid content of the tubers. In cases of simple genetic determinism (such as the Ry gene conferring resistance to the Y virus derived from Solanum stoloniferum or the R1 gene conferring resistance to late blight derived from S. demissum), the published markers were successfully validated in various genetic pools. For the H1 gene conferring resistance to G. rostochiensis, the marker available at the time of the project was found not to be linked to resistance in our material, but other markers have since been validated. In the case of oligogenic resistance, as illustrated by resistance to G. pallida—whose genetic determination is controlled by two QTLs—the transferability of four markers enabling the tracking of the high-effect QTL GpaVspl across various tetraploid gene pools was tested. Two markers for tracking the low-effect QTL GpaXIspl were also validated. All the markers have been transferred to industry partners, who are now using them at various levels within their breeding programmes. For polygenic traits (resistance to leaf blight and glycoalkaloid content), it currently seems premature to consider SAM.