Genetic Fingerprinting of Herbarium Hop Specimens Reveals Genetic Diversity and Relationships with Modern Finnish Hops

We sampled 351 hop herbarium specimens for genetic analyses of their identities through definition of unique set of samples by extraction of duplicates and comparative analyses with modern hop samples from Finland and worldwide. We also analyzed genetic diversity and assessed genetic clustering and structure within and between herbarium hops specimens and modern hop germplasm. A set of 26 previously published hop microsatellites (SSRs) proven in diversity analyses have been used for genetic evaluations of herbarium hop DNA extracted from pressed and dried specimens of which the oldest was dated back to the year of 1841. A genetic fingerprint was generated for all samples and unique ones has been generated in pairwise comparisons of pairs of samples and eliminations of duplicates. For unique set of samples, a genetic distance matrix was created for clustering analyses as well allele frequencies matrix for model-based clustering analyses. Herbarium hop samples representing historical DNA showed no clear differentiation (clustering or sub-clustering) when analyzed with presently grown modern hops. Weak tendency of hops to cluster according to the geographical origin has been noticed. We detected 39 groups of hop herbarium duplicates representing 94 specimens, where redundancy showed to be low when compared to modern Finnish hops (redundancy >70%). Analyzing herbarium hops through DNA extraction will add another link in investigating the origin and spread of Finnish hops from ancient times. Finnish hops has been described as a millennia old and native to Finland.