Structural Differences in the Intergenic Spacer of 18S-26S rDNA and Molecular Phylogeny using Partial External Transcribed Spacer Sequence in Hop, <I>Humulus lupulus</I>

Abstract

To determine the diversity within hop, Humulus lupulus, species at the molecular level, the entire intergenic spacer (IGS) of 18S-26S rDNA in hop was sequenced, and phylogenetic analyses were performed using the partial external transcribed spacer (ETS). In the IGS of the European cultivars, North American wild hops and Japanese wild hops, three types of subrepeats were identified and designated as A-, B- and C-type subrepeats, respectively. Their repetition and position were found to determine the IGS length and structural differences among them. Phylogenetic analysis using partial ETS with the related species, H. japonicus, as outgroup led to the following implications. The North American wild hops with a high alpha-acid content and disease resistance, which contribute to hop breeding, are genetically different from European cultivars, and genetic variation within North American wild hops was observed. Japanese wild hops, which have never been used for new cultivar development in the world, could be distinguished from both European and North American hops, suggesting that Japanese wild hops could be used as a new gene source for breeding.