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

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/29/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Every year hop breeding programs make crosses, evaluate new populations, and make selections with the goal of developing improved germplasm and varieties. Plants are first evaluated as seedlings, then as single individual spaced plants, and if selected, they are clonally propagated into plots, which are most representative of commercial production. It is not clear, however, how representative a hop plant’s performance as a seedling or individual spaced plant is of its performance in a plot. Despite the uncertainty, breeders often make selection decisions based on seedling or spaced-plant performance due to space and resource constraints. Considering the time and space requirements of low-density spaced plant nurseries, some breeders are selecting on seedlings while skipping the spaced plant phase. In this study, we determined that selection on seedlings for cone related traits such cone chemistry, and cone shape and size, is likely to be representative of plot performance and warrants early selection in the seedling phase. Spaced plants offered a predictive advantage for both cone traits and agronomic traits like harvest index, length of laterals, and vigor. No environment tested, besides the plots, provided an adequate representation of yield. Spaced plants are space and time consumptive, and results from the study suggest that, depending on the traits of interest, breeders may utilize performance data from the first year as seedlings to make accurate selections for advancing into plots in a more time and resource efficient manner.

Technical Abstract: Several years of the hop (Humulus lupulus L.) cultivar development process are spent evaluating genotypes in single hill, low-density plantings which generally produce insufficient volumes for testing in beer, the most important end-use trait. We evaluated the predictive ability of a genotype’s performance in the seedling year in high-density, short-trellis plantings, and in established, low-density, single hill nurseries using a full-sized trellis, on plots representative of the commercial standard to see 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 two years for agronomic traits: vigor, lateral length, yield, and harvest index, as well as cone traits: alpha and beta acid content, cone area, cone density, and cone openness. Spearman rank correlations revealed that high-density seedling evaluations were significantly predictive (a < 0.1) of the commercial standard for 33-75% of trait and year combinations. Notably, cone traits were more often significantly predictive (70% frequency, average rs = 0.80 – 0.87), than agronomic traits (12 – 38% frequency, rs = 0.87 - 0.79). Overall, the low-density, single-hill nursery offered a predictive advantage for both categories of traits (67% - 89%; rs = 0.89). From a resource use perspective, a breeder can evaluate 717% more individuals in the densest seedling configuration option relative to the least-dense single hill option. Breeders must weigh the costs of space, labor, time, and population size, and consider the predictive ability of their priority traits when deciding whether to make selections for plots directly from the first-year, high-density seedling plantings, or to first transplant selections into single hill, low-density nurseries for additional years of evaluation before advancing to plots.