Pre-harvest mechanical stress increases cannabinoid and terpene production in cannabis

Numerous stress conditions enhance secondary-metabolism in plants, and are utilized in production fields of various medicinal and aromatic plants to stimulate secondary-metabolite production. Cannabis produces hundreds of specialized metabolites, rendering it a crop of high pharmacological potential and significant health benefits. Several chemical and environmental stressors were showen to elicit changes in secondary-metabolism in cannabis. Mechanical-wounding stress is traditionally used by legacy cannabis growers under the belief that it enhances production of cannabinoids, the cannabis-specific therapeutic metabolites. However, this common notion was not tested scientifically and lacks empirical validation. Therefore, the present study evaluated the hypothesis that wounding-stress stimulates secondary-metabolite production in cannabis, and has a potential to regulate the therapeutic chemical composition. To evaluate this hypothesis, we investigated the impact of two wounding-stress practices common in traditional cannabis cultivation, stem-splitting and leaf-wounding, on secondary-metabolite production and plant physiological function. The stress was imposed pre-harvest, at the stage of intense secondary-metabolite biosynthesis. Plants were exposed to two stem-splitting treatments (applied 7 and 11-days pre-harvest), and three leaf-wounding treatments (applied 7 and 11-days pre-harvest, with two wounding intensities on day-7). The results revealed mechanical-stress stimulation of cannabinoid and terpene production, thus supporting the hypothesis. Two major cannabinoids THC and CBC, increased in response to leaf-wounding 11-days pre-harvest, but not by the other wounding treatments, supporting an interaction between wounded organ and timing of wounding. Stem-splitting 11-days pre-harvest increased concentrations of many sesquiterpenes, whereas leaf-wounding affected only a limited number of compounds, demonstrating an organ-dependent response.Taken together, the results reveal that cannabinoid and terpene biosynthesis are affected by wounding-stress in an organ, timing, and stress-intensity dependent manner. The differential effects on cannabinoids, terpenes, and individual compounds in each chemical group suggest that mechanical damage affects cannabinoid and terpene biosynthesis at distinct points of regulation downstream of the shared GPP (geranyl diphosphate) precursor.