Retrotransposon-based sequence-specific amplification polymorphism markers reveal that cultivated Pyrus ussuriensis originated from an interspecific hybridization

Retrotransposons are present in high copy number in many plant genomes. They show a considerable degree of sequence heterogeneity and insertional polymorphism, both within and between species. We describe here a polymerase chain reaction (PCR)-based method which exploits this polymorphism for the generation of molecular markers in barley. The method produces amplified fragments containing a Bare-1-like retrotransposon long terminal repeat (LTR) sequence at one end and a flanking host restriction site at the other. The level of polymorphism is higher than that revealed by amplified fragment length polymorphism (AFLP) in barley. Segregation data for 55 fragments, which were polymorphic in a doubled haploid barley population, were analysed alongside an existing framework of some 400 other markers. The markers showed a widespread distribution over the seven linkage groups, which is consistent with the distribution of the Bare-1 class of retrotransposons in the barley genome based on in situ hybridisation data. The potential applicability of this method to the mapping of other multicopy sequences in plants is discussed.