Internode elongation and strobili production of Humulus lupulus cultivars in response to local strain sensing

Three different cultivars of Humulus lupulus L. were subjected to a regime of internode touch and bending under greenhouse conditions. Experiments were performed to assess intraspecific variability in plant mechanosensing, flower quality, and yield to quantify the thigmomorphogenic impact on plant compactness and flowering performance. Touching and/or touching plus bending the plant shoot internodes located in the apical meristem zone decreased internode elongation and increased width. The growth responses were due partly to touching and/or touching plus bending perturbation, 25.6% and 28% respectively. Growth of new tissue within the local apical portion of the bine continued to remain mechanosensitive. The number of nodes and female flowers produced was unaffected by either type of mechanical stress. The study provides evidence that thigmomorphogenic cues can be used as a hop crop management tool to increase bine compactness and increase node density per unit area. The findings have broad implications for hop production; production can more readily take place in a confined greenhouse space with the aid of mechanical stimulation to control plant growth without sacrificing yield or flower quality.