Population Structure and Genetic Diversity of Castanea sativa Mill. Genotypes in the Republic of Croatia

The European sweet chestnut (Castanea sativa Mill.) is an ecologically and culturally significant forest tree species in Croatia; however, its genetic diversity and population structure remain insufficiently characterized. This study aimed to evaluate the genetic diversity, structure, and connectivity of chestnut populations on Zrin Mountain, the country’s largest continuous chestnut area. Using seven nuclear SSR markers, we genotyped 153 individuals from three populations (PET, HRK, and BAC). All populations exhibited moderate genetic diversity (mean He = 0.571), with BAC showing the highest allelic richness and number of private alleles. AMOVA revealed that most genetic variance (67%) occurred among individuals, while population differentiation was low to moderate (FST = 0.064; PhiPT = 0.146), consistent with high inferred gene flow (Nm = 7.48). Both STRUCTURE and PCoA indicated that HRK was the most genetically distinct population, whereas PET and BAC were more similar. Overall, these findings demonstrate substantial gene flow and connectivity among Croatian chestnut populations, providing a foundation for sustainable management and conservation strategies in a broader European context.