Genetic, phytochemical and agronomic characterization of wild hop ecotypes from Switzerland

Hop (Humulus lupulus L.) is a herbaceous liana of the hemp family (Cannabaceae) that have been used for centuries mainly to flavor and preserve beer. Swiss hop production is relatively modest, with the six main producers supplying only about 10% of national demand. However, the Swiss production is set to grow in the coming years as hundreds of new breweries have recently been established and are looking to source malt and hop locally. Switzerland has numerous natural hop ecotypes that grow in all major biogeographical regions. These ecotypes are adapted to the soil-climatic conditions of Switzerland and may be a source of resistance genes against pests and diseases of this aromatic plant. Wild hops can be used directly for beer brewing, but can also offer the potential for development of new varieties by crossing and combining favorable traits with elite varieties. Initiated in 2019, the goal of this study is to collect wild hop populations across Switzerland to characterize their bitter acid content, volatile profile and genetic diversity. Here, we present preliminary results on yield and phytochemical composition obtained in 2020 with a subset of the current collection and a selection of elite cultivars. In this first year of cultivation, wild hop ecotypes tend to produce more yield (female flowers) than elite cultivars with a large diversity in plant and flower morphology, as well as in phenological development. Alpha and beta acids content of Swiss wild hop is relatively homogenous and rather low (between 2 and 4%), as it has been described for wild European ecotypes and elite variety bred for aroma. Essential oil content in flowers of this population subset ranges between 0.2 and 0.6%, which appears to be lower than elite variety used for comparison (0.3-1%). Headspace GC-MS analysis of flowers show a tremendous diversity in the volatilome of female flowers. We identified several volatile metabolites such as beta-bisabolol, aromadendrene and cyperene that were present only in some ecotypes at very different concentrations. From 2022, the whole collection, now consisting of 70 ecotypes, will be cultivated and analyzed during multiple years to fully assess the agronomic performance, and the phytochemical and genetic diversity of Swiss wild hops.