Abstract
Humulus lupulus L. (hop) flowers are a key ingredient in beer, imparting the beverage’s aroma and bitterness profile. Photoperiod is known to interact with temperature to control flowering in hops. Studies have stipulated that resting dormant buds on hops require a minimum chilling duration for their meristems to break dormancy and grow fruitfully. This assertion, in part, led to a long-held notion that hops require vernalization and/or dormancy for the meristem to change from a vegetative to floral state. The research in this study aims to separate photoperiod from vernalization and dormancy through a series of experiments that artificially control photoperiod to prevent the onset of dormancy and chilling exposure. Six experiments were performed to assess flower yield and quality for seven diverse hop cultivars (with and without exposure to chilling and dormancy) to quantify the impact on flowering performance. Vernalization and dormancy, two plant traits previously considered necessary to the proliferation of hop flowers, do not influence hop flower yield and quality. The findings have broad implications; global hop production can be distributed more widely and it paves the way for speed breeding and controlled-environment production to achieve 4 hop generation cycles per year, as opposed to 1 under field-grown conditions.
Highlights
Humulus lupulus L. flowers are a key ingredient in beer, imparting the beverage’s aroma and bitterness profile
Given that the yield and quality of the global hop supply are heavily influenced by these two climate factors, modern controlled environment technologies could be adopted to modify microclimate conditions and offer a broadly applicable hop production alternative
In one of the seminal books on hops, Neve and colleagues stipulated that resting dormant buds on hops require a minimum chilling duration of 42 days at 3 °C for their meristems to break dormancy and grow fruitfully[9]
Summary
Humulus lupulus L. (hop) flowers are a key ingredient in beer, imparting the beverage’s aroma and bitterness profile. The increasingly shorter autumn day lengths initiate a gradual shoot death and the onset of dormancy by early winter[6] At this point, vernalization completes the cycle, the process by which plants become competent to flower after exposure to prolonged winter chilling e.g.7,8. In one of the seminal books on hops, Neve and colleagues stipulated that resting dormant buds on hops require a minimum chilling duration of 42 days at 3 °C for their meristems to break dormancy and grow fruitfully[9] From their reports on chilling and dormancy, this assertion, in part, led to a long-held notion that hops require vernalization and/or dormancy for the meristem to change from a vegetative to floral state. Vernalization and dormancy have been accepted as flower induction prerequisites for hops e.g.9,10, the author knows of no published data to substantiate or refute the necessity for either low temperature chilling or a dormant phase and no published data are available that equate chilling hours with hop flower induction and proliferation
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