Agronomic, genetic and chemical tools for hop cultivation and breeding

Humulus lupulus L. (hop)is a dioecious climbing plant of which the females bear particular inflorescences, called hops, 'cones' or 'strobiles', made of a series of membranaceous bracts and bracteoles. At the base of these 'cones' occur glandular trichomes where a complex metabolome is synthesized mainly consisting of terpenoids (constituents of essential oil)and original prenylated phenolic compounds. These latter are represented by acylphloroglucinols including ?-acids (humulone and its derivatives)and ?-acids (lupulone and its derivatives), as well as chalcones (xanthohumol and desmethylxanthohumol). Some of these compounds, terpenoids and sulfur-containing compounds from essential oils and ?-acids, are particularly sought after by brewers because they impact bitterness, aroma, flavour and storage properties of beer. Yield of ?-acids and bittering performance drove selection of cultivars until demand for alternative flavour options from craft brewers emerged. More aromatic cultivars with intense fruit-like character have been in high demand in recent years due to the trend for hoppy beers and dry hopping. Moreover, there is a tendency toward local consumption associated with craft beer. In addition, consumers and producers are understanding the concepts of sustainability, partially driven by perception of the effects of anthropogenic climate change. Finally, traditional supply chains are facing legitimate challenges from small scale local producers. This review presents the current challenges of hop production and appraises the tools available to investigate the genetic and chemical diversity of this plant.