Genetic analysis of Latvian Salix alba L. and hybrid populations using nuclear and chloroplast DNA markers

Latvia is at the northern border of the species range of S. alba L. in Europe, and there has been some debate whether the Latvian populations of S. alba are autochthonous, as this species has long been planted in Latvia as an ornamental tree in gardens, parks and roadsides. In addition, there is increasing interest in the use of several Salix species (including S. alba) as bioenergy crops. Natural S. alba stands throughout Latvia, as well as stands of possibly hybrid origin were analysed using nuclear and chloroplast markers. Our results showed that S. alba populations are probably natural, and that the rate of vegetative reproduction is low, supporting the evidence that Latvia is within the natural range of S. alba. These results provide the basis for the identification of possibly introduced or artificially regenerated stands of S.alba in Latvia. In addition, our results confirm that S. alba hybridises with S. fragilis, and that natural stands including hybrid individuals can be established. The analysis of chloroplast markers indicated that the predominant hybridisation occurs by fertilisation of S. fragilis by S. alba pollen; however, the extent of haplotype sharing between these two species should be further investigated.