Genetic relationship between Pinus species (P. densiflora, P. thunbergii, P. thunbergii 'Kumyahuksong') in the democratic people's Republic of Korea

Pinus densiflora and Pinus thunbergii are important forest tree species in the DPR Korea due to their ecological adaptability and versatile uses, including timber, medicinal, and cosmetic production. P. thunbergii 'Kumyahuksong' is a significant windbreak tree species on the coast due to its high salt tolerance, pest resistance, and rapid growth. Understanding the genetic relationships of Pinus species, with the potential for natural crosses, would assist forest establishment and conservation strategies. In this study, the genetic relationship among 63 germplasms of pine species were analyzed using RAPD and ISSR markers. The populations of both species and cultivars displayed significant genetic differentiation, as evidenced by the high F-ST values ranging from 0.53 to 0.72. PCA and UPGMA clustering analyses revealed that the samples could be separated into major clusters according to their species. Firstly, P. densiflora and P. thunbergii were separated, followed by the separation of P. thunbergii 'Kumyahuksong'. The Bayesian Structure analysis further emphasized the distinctiveness of P. thunbergii 'Kumyahuksong', particularly at K = 3, where it was presented as a distinct group. Despite the 'Kumyahuksong' cultivar indicated higher inbreeding (FIS = 0.261), it was also found to have a higher number of observed and effective alleles and polymorphisms compared to P. thunbergii. These results confirm the cultivar status of P. thunbergii 'Kumyahuksong', and also indicate that its exceptional phenotypic characteristics are likely due to its specific genetic background. Identification of natural crosses and fingerprinting of such individuals are valuable to effectively select materials in breeding programs of P. thunbergii, and the related species.