Towards the onset of fruit tree growing north of the Alps: ancient DNA from waterlogged apple (Malus sp.) seed fragments.

Wild apples (Malus sp.) have been a major food source in the northern Alpine region since prehistory and their use is well understood. The onset of deliberate fruit tree growing in the area is, however, less clear. It is generally assumed that horticulture was practised in Roman times, but it might be even earlier. In the archaeological record seed testa and pericarp remains are particularly frequent at sites with waterlogged preservation such as lakeshore settlements or wells, pits and ditches, but the distinction between wild and domestic plants is not morphologically possible. With waterlogged remains being one main source of information about past fruit cultivation, we have tested the feasibility of analysing ancient DNA from waterlogged preserved bulk samples of testa fragments. We studied apple seeds from three Neolithic and three Roman sites with waterlogged preservation in the Alpine foreland. Chloroplast markers failed in all samples, but nuclear ITS1 (internal transcribed spacer region 1) of the ribosomal DNA was successfully typed in two Roman samples from the site Oedenburg/Biesheim-Kunheim (Haut-Rhin, F). The retrieved ITS1 sequences are identical to each other and are shared with wild Malus sylvestris and Malus sieversii, and with domestic apple cultivars, supporting the potential of using waterlogged remains for identifying the genetic status of apple diachronically.