Predictive ability of hop (Humulus lupulus L.) grown in single hills on plot environments

Several years of the hop (Humulus lupulus L.) cultivar development process are spent evaluating genotypes in single hill, low-density plantings. We evaluated the predictive ability of a genotype's performance in the seedling year in high-density, short-trellis plantings, in established, low-density, single-hill nurseries, and on plots representative of the commercial standard. The objective was to determine whether the single hill phase could be eliminated in favor of advancing from seedlings directly into plots. We tested seven hop genotypes across five spacing and trellis height configurations for 2 years for agronomic traits and cone traits. Spearman rank correlations revealed that high-density seedling evaluations were significantly predictive (average ρ = 0.60; α < 0.1) of the commercial standard for 44%–75% of trait and year combinations. Notably, across all spacings, cone traits were more often significantly predictive (75%–85% frequency, average ρ = 0.78–0.82) than agronomic traits (38%–56% frequency, ρ = 0.52–0.64). Overall, the low-density, single-hill nursery offered a predictive advantage over the seedlings for both categories of traits. From a resource use perspective, 717% more individuals can be evaluated in the densest seedling option relative to the least-dense single hill option. Breeders must weigh the costs of space, time, population size and the predictive ability of their priority traits when deciding whether to make selections from the first year or to first transplant selections into single hill nurseries for additional years of evaluation.