Genetic insights into the hybrid origin of Abies × borisii-regis Mattf

Abies × borisii-regis Mattf. (King Boris fir) is a taxon endemic to the southern Balkan Peninsula, described as a hybrid between the widespread A. alba Mill. (Silver fir) and the Greek endemic A. cephalonica Loud (Greek fir). Even though A. × borisii-regis has attracted much research attention in the past, its origin, geographical distribution and taxonomic status are not fully elucidated and molecular evidence for hybridization is missing. To shed more light on this issue, we analyzed representative populations from these three Abies taxa using paternally inherited (chloroplast) and maternally inherited (mitochondrial) DNA markers. Both Silver and Greek fir could be clearly distinguished using mitochondrial markers, while we observed a mixture of maternal lineages in the A. × borisii-regis populations. In contrast, using chloroplast markers, we could not identify species-specific haplotypes, but a neighbor-joining analysis of population genetic distances revealed two separate clusters for the Silver fir and the Greek fir, while the A. × borisii-regis populations were placed in intermediate positions. Our results are in agreement with the hypothesis that the A. × borisii-regis populations investigated are a result of hybridization between A. cephalonica and A. alba.