Field-Based Estimates of Heritability and Genetic Correlations in Hop

Early selection efforts in hop breeding consisted solely of clonal selection, with most male hop plants rogued out Hop (Humulus lupulus L. var. lupulus) is grown worldwide for from localities where hops are produced. Only within the the production of the dried female inflorescence (strobulus), or cones, used principally for the bittering and flavoring of beer. Information last half-century have major efforts been made to utilize is scant on the inheritance of traits of economic importance in hop, male hop lines in breeding programs. Because of the andpresentknowledgeisbasedonhistoricaldataratherthandesigned paucity of male hop lines and the insistence by major experimental investigation. The objective of this study was to estimate brewers on using specific established hop varieties, little the heritability of and genetic correlation among six traits: yield information has accumulated regarding the genetics of (YLD), -acid (ALP) concentration, -acid (BET) concentration, breeding this species, other than early work by Keller cohumulone (COH) percentage, colupulone (COL) percentage, and and Likens (1955) and work using historical data for xanthohumol(XAN)concentration.Twenty-fivefull-sibfamilieswere estimates of heritability (Henning et al., 1997a, 1997b). developed by crossing five randomly chosen females and five ranFurthermore, the lackof male lines hasrestricted efforts domly chosen males in a North Carolina Design II mating design. by researchers to estimate maternal and paternal effects Plants were transplanted into the field in a randomized complete block (RCB) design with four replicates. Data were recorded for two in genetic studies. Initial reports on hop breeding dealt years. Heritabilities for all traits were moderate to high using variance primarily with technique and strategy with little inforcomponents estimated from males. With the exception of heritability mation on the heritabilities of, or genetic correlations beestimates for YLD and ALP, all other traits were not significantly dif- tween, traits of interest (Haunold,1980, 1981; Neve,1991; ferent from zero using female variance components as estimators. Roberts et al., 1980). Keller and Likens (1955) and RobPooled estimates of heritability yielded more reasonable estimates erts et al. (1980) both reported on heritability in hops. with lowest heritability for BET (h 2 0.57 0.19) and highest for Unfortunately, both papers reported heritability estiCOL(h 2 0.890.02).Pooledestimatesofgeneticcorrelationsranged mates that were biased upward because of confounding from r 0.28 (ALP and YLD) to r 0.92 (YLD and XAN). Finally, of the additive genetic variance with dominance variance. correlations between coefficients of coancestry (COA) between pairs Much of the preliminary efforts at breeding hops and their respective mean offspring data were significant for ALP, COL, and XAN suggesting that for these traits at least, COA values through cross-fertilization focused primarily on choice may be predictive of potential heterosis. On the basis of these data, of female lines for crossing; the male parent viewed selection for COL, ALP, and YLD would be successful using simple solely as a means to obtain offspring for selection. Initial selectionprotocolssuchasphenotypicrecurrentormassselection.The genetic work by Henning et al. (1997a) demonstrated likelihood of success when selecting for BET and XAN would be low, that significant genetic variation was present in male thus requiring one of the genotypic recurrent selection techniques. lines, which could be utilized to choose specific males Selection against COH (a negative factor in brewing) appears prob- for crossing purposes on the basis of general combining lematic because of positive correlations with all other traits. The in- ability (GCA) and also specific combining ability (SCA). formation presented in this study is the first published record of field