Separate and Combined Effects of Supplemental CO₂, Gibberellic Acid, and Light on Hop Quality and Yield

We investigated the effect of supplemental CO₂, gibberellic acid (GA₃), and light on the quality and yield of Humulus lupulus L. strobili (cones). When applied separately, CO₂ and light increased the yield by 22% and 43%, respectively, and had a significant effect on the components of cone mass and quality. Exogenous GA₃ increased flower set; however, the yield decreased by approximately 33%. Combining CO₂, GA₃, and light, and any combination thereof, resulted in significant increases in flower set and cone yield enhancement compared to separate applications. A synergistic effect occurred when some factors were combined. For example, the combination of CO₂ and light resulted in a yield increase of approximately 122%. The combination of all three resources, CO₂, GA₃, and light, resulted in an approximate 185% yield increase per plant. Thus, in comparison to the addition of one supplementary resource, a greater increase in yield resulted from the combination of two or more supplemental resources. Flower set stimulation due to GA₃ decreased cone alpha- and beta-acid quality attributes, unless combined with CO₂ and light as additional carbohydrate-generating resources. Additional research is needed to close the hop yield gap between current hop yields and the achievement of the plant's genetic potential.