Identification of traditional Galician sweet chestnut varieties using ethnographic and nuclear microsatellite data

Traditional varieties are the basis of most chestnut production in Europe. Until recently, cultivation practices were transmitted orally, and trees in orchards were grafted using local varieties. Traditional methods are being replaced by controlled plant certification and nursery propagation. Starting materials must consequently be confirmed to be representative of desired cultivated varieties. Such an objective requires knowledge of the varietal structure of traditional orchards. This information may be acquired through the development of varietal inventories with names of cultivated varieties and their geographic dispersion followed by genotypic and phenotypic characterization of accessions representing target varieties. In this study, accessions of traditional varieties cultivated in orchards of Galicia (northwestern Iberian Peninsula) were genotyped with 10 nuclear microsatellites to identify different cultivated clones. Multilocus genotypes were obtained from 26 traditional varieties. The high number of closely related genotypes that were uncovered can be attributed to prolonged cultivation and hybridization between individuals constituting one or several landraces developed over centuries. These results were used to examine the adequacy of the conducted sampling for defining clones, assigning names and synonyms, and for acquiring information on various other aspects. Finally, terms useful for the study of traditional chestnut varieties were defined, and several tips for identifying traditional varieties were suggested. From the genetic point of view, a sweet chestnut traditional variety could be monoclonal, polyclonal, or a multiline variety; however, a commercial chestnut clone is monoclonal but it must also meet DUS conditions imposed on commercial varieties.