Abstract
BackgroundMost traits targeted in the genetic improvement of hop are quantitative in nature. Improvement based on selection of these traits requires a comprehensive understanding of their inheritance. This study estimated quantitative genetic parameters for 20 traits related to three key objectives for the genetic improvement of hop: cone chemistry, cone yield and agronomic characteristics.ResultsSignificant heritable genetic variation was identified for α-acid and β-acid, as well as their components and relative proportions. Estimates of narrow-sense heritability for these traits (h 2 = 0.15 to 0.29) were lower than those reported in previous hop studies, but were based on a broader suite of families (108 from European, North American and hybrid origins). Narrow-sense heritabilities are reported for hop growth traits for the first time (h 2 = 0.04 to 0.20), relating to important agronomic characteristics such as emergence, height and lateral morphology. Cone chemistry and growth traits were significantly genetically correlated, such that families with more vigorous vegetative growth were associated with lower α-acid and β-acid levels. This trend may reflect the underlying population structure of founder genotypes (European and North American origins) as well as past selection in the Australian environment. Although male and female hop plants are thought to be indistinguishable until flowering, sex was found to influence variation in many growth traits, with male and female plants displaying differences in vegetative morphology from emergence to cone maturity.ConclusionsThis study reveals important insights into the genetic control of quantitative hop traits. The information gained will provide hop breeders with a greater understanding of the additive genetic factors which affect selection of cone chemistry, yield and agronomic characteristics in hop, aiding in the future development of improved cultivars.
Highlights
Most traits targeted in the genetic improvement of hop are quantitative in nature
Genetic variation Significant genetic variation was found between families for all cone chemical traits assessed (Table 1)
No significant genetic variation was found between families for cone yield (Table 1); but significant genetic variation was found between families for all plant growth traits (Table 1)
Summary
Most traits targeted in the genetic improvement of hop are quantitative in nature. Improvement based on selection of these traits requires a comprehensive understanding of their inheritance. The resins found in hop lupulin glands have not been found in any other plant species [9]; they comprise hard resins (including xanthohumol, iso-xanthohumol and flavone) and soft resins ( called hop acids), which are dominated by humulones (α-acids) and lupulones (β-acids) [10,11]. It is the α-acids that provide the bitter taste to beer [9]. Hops have a native distribution between latitudes of approximately 35° and 70° North, from Western Europe, east to Siberia and Japan and across North America, except in highlands and deserts [21,22], but many hop cultivars are of European genetic origin, or are hybrids between European and North American germplasm [9,23]
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