Molecular phylogeny of wild hops, Humulus lupulus L.

We have analysed wild hops collected widely from the Northern Hemisphere, assessing the genetic diversity and the geographical distribution of haplotypes, to investigate the evolution and phylogeny of hops, Humulus lupulus. The haplotypes were characterized by the nuclear ribosomal DNA spacer region (length and DNA sequence) and chloroplast DNA noncoding regions (DNA sequences). The results indicated that primary divergence into European (including Caucasus and Altai hops), and Asian-North American types, was 1.05+/-0.28 to 1.27+/-0.30 million years ago. Although an Eastern boundary for European nuclear haplotype distribution was unclear due to the ambiguous origin of Northern Chinese samples, the European hop group showed a wide geographical distribution across Eurasia from the Altai region to Portugal. The low genetic variation in this group suggested rapid and recent expansion. The North American hop group showed high diversity, and is considered to include hops that have migrated from Asia. Japanese and Chinese hops were identified as genetically distinct. This study has shown that wild hops in each growing region are genetically differentiated with considerable genetic diversity. It gives insights into the evolution and domestication of hops that are discussed.

Identification of sex in hop (Humulus lupulus) using molecular markers.

The rapid identification of sex in the dioecious hop (Humulus lupulus) is important for the breeding of this cultivated plant because only unfertilized flowers of the female plants are used as an ingredient in the production of beer. It is thought that a sex-chromosome mechanism controls the development of male or female plants. We have compared pools of male and female plants derived from a hop cross to identify molecular markers associated with the Y or male-specific chromosome. Of 900 functional RAPD primers, 32 revealed fragments specific for male plants that were absent in female plants of this cross. Subsequently, the 32 positive primers were tested on unrelated male and female plants. Three of these 32 primers were specific for the Y chromosome in all lines. The Y-specific product derived from one of these primers (OPJ9) was of low copy in hybridization experiments and predominantly present in male plants. Primers developed from the DNA sequence of this product provide a marker for rapid sex identification in crosses of hop by means of PCR.