Genetic variation in Danish and Norwegian germplasm collections of hops

Abstract

The germplasm collections of hops (Humulus lupulus L.) in Denmark and Norway are maintained in clonal archives funded by the national authorities. The plants have been collected over the last decades as part of a strategy to conserve plant genetic resources for future generations. The major part of the various collections consist of plants collected in villages and gardens. About 20% are plants used for breeding, mainly kept in a collection at Carlsberg, Denmark. In order to identify any duplicates and with a view to learning more about the various collections, a DNA fingerprinting study was initiated, analysing 62 Danish and 34 Norwegian clones with a set of five amplified fragment length polymorphism (AFLP) markers. The AFLP analyses resulted in 41 polymorphic bands and were able to separate the majority of the Danish and the Norwegian accessions. UPGMA dendrograms showed 21 accession groups, and potential duplicates were found within 13 of these groups. Principal coordinates analysis revealed that plants were differentiated according to country of origin. In addition, regional separation of the plants within each country was also detected, and similar levels of diversity were found in the Danish and the Norwegian collections. Compared to the rest of the plants, there was less diversity within the Carlsberg material. For the Norwegian as well as a part of the Danish collection, morphological characterisation and chemical analysis was carried out, allowing a comparison of these to the AFLP data. A correlation with AFLP bands and both morphological and chemical characteristics was detected. The most promising results for further breeding was an association of AFLP bands with the content of colupulon in the cones, measured by relative values compared to the total alpha acid content. Further studies are needed to verify such an association with the potential to develop a PCR-based marker for hop breeding carried out in the clones now analysed with AFLP markers, making it possible to search for any association between AFLP data and phenotypic data.