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.