Crossability of Putative Hybrids of Pinus sylvestris and Pinus mugo with Their Parents

Artificial hybridization experiment with the Pinus sylvestris and Pinus mugo putative hybrid individuals and their parents revealed a selective nature of their crossability conditioned by the identical chloroplast DNA (cpDNA) haplotypes of the crossed individuals. Efficiency of hybridization between hybrid individual H1 of P. sylvestris haplotype and P. sylvestris paternal tree was relatively high, as evidenced by 78.03% of filled seeds. On the contrary, the crossing of H1 individual with P. mugo was unsuccessful. Likewise, the crossability of the H2 individual of P. mugo haplotype with the paternal tree P. mugo resulted in 31.15% of filled seeds. A relatively high crossability was characteristic also for the H1 and H2 hybrid trees of different cpDNA haplotypes. A conclusion has been drawn postulating weakened reproduction barrier between hybrid swarm individuals and the paternal species P. sylvestris and P. mugo. Differentiation of the putatively hybrid individuals from the parental species is accompanied by the variation in cpDNA inheritance.