Exploring the tropical acclimation of European and American hop cultivars (Humulus lupulus L.): Focus on physiology, productivity, and chemical composition

Hop (Humulus lupulus L.) cones are widely used by the beer industry to provide flavor, aroma, and bitterness due to the presence of α-acids, β-acids, and volatile oil components. Although the brewing sector plays an important role in Brazil’s economy, hops are entirely imported. In this study, we aimed to investigate the physiological acclimation potential, productivity, and chemical composition of four hop cultivars in a warm tropical region of Brazil. For this purpose, three North American-bred hop cultivars (‘Cascade’, ‘Chinook’ and ‘Triple Pearl’) and one European hop cultivar (‘Saaz’) that grew under tropical ambient conditions for two consecutive years were used. ‘Saaz’ and ‘Triple Pearl’ showed higher mortality and smaller photosynthetic rates, while ‘Cascade’ and ‘Chinook’ cultivars showed the best physiological and growth performance under a tropical-type climate. With a few exceptions, maximum quantum yield of photosystem II (PSII), chlorophyll content, and antioxidant enzymes activity were very similar between these two cultivars. A higher dry mass of cones was observed in ‘Chinook’ and ‘Cascade’, however, with a higher variability within each cultivar. Both cultivars increased the production of the dry mass of cones in the second year. The average concentration of bitter acids in ‘Cascade’ and ‘Chinook’ was below the expected values, but there was a considerable increase in the volatile oil content between the first and second year of cultivation. We concluded that 'Cascade' and 'Chinook', American cultivars, showed better development and lower mortality compared to 'Triple Pearl' (American cultivar) and 'Saaz' (European cultivar) under tropical climate conditions in Brazil. Although the concentration of bitter acids was lower than expected in the first two years, the concentration may increase with plant maturity.