Marker- and genomics-assisted assessments over three decades across Europe reveal substantial genetic diversity and adaptive potential in pedunculate oak (Quercus robur L.), informing operational conservation strategies

This review synthesizes three decades of molecular evidence on the genetic diversity and conservation of pedunculate oak (Quercus robur L.) across Europe. A methodological synthesis delineates three phases of marker evolution: Phase I (1993–2003) – isozymes, RAPD, AFLP and early SSRs establishing population-genetic baselines; Phase II (2004-2014) – multi-marker integration and QTL analyses linking marker variation to adaptive traits; and Phase III (2015–2026) – the genomic era with WGS, SNP, ddRADseq and GBS systems enabling high-resolution inference of demography and local adaptation. Genetic diversity of Q. robur was assessed using allelic richness, observed and expected heterozygosity, fixation and differentiation indices, chloroplast haplotype diversity and SNP-based genomic metrics, consistently showing high within-population diversity, low but significant among-population differentiation maintained by extensive gene flow and spatially structured adaptive variation shaped by postglacial history and environmental gradients, confirming strong evolutionary and adaptive capacity across Europe. Integrating SSR, SNP and phenotypic evidence reveals robust adaptive potential to drought and water stress. Based on these findings and EUFORGEN guidance, a tiered conservation strategy is proposed: (i) in situ preservation of large, interbreeding stands; (ii) provenance-based seed transfer within seed zones; (iii) ex situ conservation of marginal populations; and (iv) circa situm management in productive landscapes. This synthesis establishes a marker-informed framework linking evolutionary processes to actionable conservation, thereby strengthening the adaptive capacity of Q. robur under climate change across Europe.