Italian hop germplasm: Characterization of wild Humulus lupulus L. genotypes from Northern Italy by means of phytochemical, morphological traits and multivariate data analysis

To evaluate the intraspecific diversity of wild Humulus lupulus in Northern Italy, 22 hop accessions were collected from distinct populations. The selected germplasm was genetically probed with 9 SSR primers, grown in a collection field and compared with 5 commercial varieties (Columbus, Fuggle, H. Magnum, Tettnanger, Willamette) cultivated under the same conditions. Hops were evaluated for their aromatic profile, xanthohumol and bitter acids composition by means of GC–MS and HPLC-UV, and further analyzed by principal component and cluster analysis. A great phytochemical diversity was found and wild populations were classified in three distinct clusters in terms of volatile composition and in two separate groups in terms of bitter substances content. Multivariate data analyses revealed that selinenes, α-acids, trans-β-farnesene and α-caryophyllene/β-humulene ratio, both contribute the most to the classification of Italian genotypes. Xanthohumol and α-acids content were higher than previously reported for European wild hops. Total α- and β-acid content ranged between 2.98 g/100 g (Busseto 13) and 11.11 g/100 g (Rio Gambero). In the volatile fraction, selinene isomers were above 40% in the essential oils isolated from 6 samples; myrcene ranged between 0.5 (Pasqui 1) and 30% (ET8), while α-humulene/β-caryophyllene ratio was comprised between 0.26 (ET8) and 4.16 (Roggino 2). The phytochemical variability and the presence of traits valuable for brewing suggest the potential exploitation of some ecotypes for breeding and improvement of the cultivated varieties, in particular for plant material aimed to be used in the dry hopping stage of brewing. Some wild genotypes may be valuable as dual purpose or aromatic hops, with properties similar to Fuggle and Tettnanger. The results of the first comparative report of commercial H. lupulus cultivars in Italy are also reported.