Patterns of genetic variation and the potential origin of sweet chestnut (Castanea sativa Mill.) stands far from its natural northern distribution edge

Castanea sativa Mill. is an important European tree species that has been used for timber and nut production since Greek and Roman times. In Germany, the species accounts for only a small proportion of forest stands but it is attracting increasing interest due to its possible potential for climate tolerance and resilience. However, the status of German sweet chestnut stands in terms of genetic diversity and adaptive potential is poorly investigated. We took a representative sample of 520 individuals from 13 stands in northern Germany (Mecklenburg Western Pomerania; MWP) and genotyped these at 11 genomic SSRs and EST-SSRs. In addition, we compared our data with the available literature, focusing on the possible origin of the MWP populations. The analysis of genetic structure identified three distinct genetic groups within MWP, suggesting different origins or seed mixtures of various provenances. The comparison with reference data at the EST-SSR FIR059 suggests that the MWP stands originate from the western gene pool. The genetic variation observed in most MWP stands is at approximately the same level as stands in the natural range. Therefore, these stands with high diversity seem to be particularly suitable for further production of seed and plant material in MWP. This study contributes to the understanding of the genetic diversity and origin of sweet chestnut stands outside their natural distribution in MWP. It provides valuable knowledge for the evaluation and conservation of genetic resources of this tree species, which is expected to receive more attention under warmer and drier conditions.