Field-based estimates of heritability and genetic correlations in hop

Hop (Humulus lupulus L. var. lupulus) is grown worldwide for the production of the dried female inflorescence (strobulus), or cones, used principally for the bittering and flavoring of beer. Information is scant on the inheritance of traits of economic importance in hop, and present knowledge is based on historical data rather than designed experimental investigation. The objective of this study was to estimate the heritability of and genetic correlation among six traits: yield (YLD), alpha-acid (ALP) concentration, beta-acid (BET) concentration, cohumulone (COH) percentage, colupulone (COL) percentage, and xanthohumol (XAN) concentration. Twenty-five full-sib families were developed by crossing five randomly chosen females and five randomly chosen males in a North Carolina Design II mating design. Plants were transplanted into the field in a randomized complete block (RCB) design with four replicates. Data were recorded for two years. Heritabilities for all traits were moderate to high using variance components estimated from males. With the exception of heritability estimates for YLD and ALP, all other traits were not significantly different from zero using female variance components as estimators. Pooled estimates of heritability yielded more reasonable estimates with lowest heritability for BET (h(2) = 0.57 +/- 0.19) and highest for COL (h(2) = 0.89 +/- 0.02). Pooled estimates of genetic correlations ranged from r = 0.28 (ALP and YLD) to r = 0.92 (YLD and XAN). Finally, correlations between coefficients of coancestry (COA) between pairs and their respective mean offspring data were significant for ALP, COL, and XAN suggesting that for these traits at least, COA values may be predictive of potential heterosis. On the basis of these data, selection for COL, ALP, and YLD would be successful using simple selection protocols such as phenotypic recurrent or mass selection. The likelihood of success when selecting for BET and XAN would be low, thus requiring one of the genotypic recurrent selection techniques. Selection against COH (a negative factor in brewing) appears problematic because of positive correlations with all other traits. The information presented in this study is the first published record of field-based estimates of narrow-sense heritability and genetic correlations in hop and will aid hop breeders working with these traits.