Evidence of natural reciprocal hybridisation between Pinus uliginosa and P. sylvestris in the sympatric population of the species

Peat-bog pine Pinus uliginosa Neumann has become extinct or rare in many parts of Europe. It is supposed to hybridize with P. sylvestris but the influence of hybridization to genetic erosion of the P. uliginosa gene pool is unknown. In the presented study, the crossability between P. uliginosa and P. sylvestris was analyzed in a sympatric population at Węgliniec reserve in Poland. The aim of the study was to prove natural hybridisation and to estimate the influence of this phenomenon on possible natural gene pool erosion of peat-bog pine. A sequence polymorphism in the trnF–trnL cpDNA region of P. uliginosa and P. sylvestris was used to develop the species diagnostic PCR-RFLP marker. The marker of paternally transmitted cpDNA was applied in haplotype analyses of the progeny from open-pollinated P. uliginosa seeds (collected in 2000–2002) and from P. sylvestris ones (in 2002). An inconsistency in species diagnostic cpDNA haplotypes of seedlings and parental trees was observable both for P. uliginosa and P. sylvestris (about 1% and 2% of hybrids seeds, respectively). The results prove the occurrence of reciprocal hybridisation between the species. The influence of hybridisation on the natural gene pool protection and measures to reintroduce peat-bog pine is discussed.