Interactive Effects of Methyl Jasmonate, Cultivar, and Insecticide Treatments on Agronomic and Phytochemical Traits of Cannabis sativa L.

The reform of laws surrounding the cultivation of cannabis ( Cannabis sativa L.) in recent years has sparked the revitalization of its use for fiber, food, medicine, and recreational purposes. Although the cultivation of high-cannabidiol (CBD) cannabis is now legal with proper documentation, growers face challenges associated with decades of prohibition, creating a gap in knowledge and the need for novel cultivation techniques to improve production standards. A significant determinant of quality and potentially yield in cannabis is the density of glandular trichomes and the concentration of cannabinoids these structures contain. Techniques that could manipulate these properties would be inherently valuable to cultivation outcomes. A field experiment was conducted in the summers of 2021 and 2022 to assess the effects of methyl jasmonate (1 mM MeJA), cultivars (Cherry Citrus, Baox, Super CBD in 2021; Cherry Citrus, Stout, Super CBD in 2022), and insecticide treatment on yield-related traits and cannabinoid concentration in cannabis. The insecticide treatment aimed to suppress herbivory, which can independently trigger MeJA release and thereby introduce unwanted variation into the study. Exogenous MeJA increased trichome density in 2022 but not 2021; however, no increases in cannabinoid concentration [CBD or tetrahydrocannabinol (THC)] accompanied this response in either year. Cultivars significantly differed for plant height and width (both years) and for biomass (wet, dry, and bucked) in 2022, with Stout producing the greatest size and biomass of the three cultivars. Cultivar effects were also significant for trichome density, total CBD, and total THC. Interactions between cultivar and insecticide affected CBD in 2022, and a marginal cultivar × insecticide interaction occurred for total THC in 2022. Insecticide application reduced herbivory damage in 2021. Overall, these results indicate that MeJA can stimulate trichome formation without necessarily increasing cannabinoid accumulation, suggesting genotype-dependent regulation of MeJA-responsive pathways. Further research can focus on detecting how MeJA timing, rate, and cultivar choice interact with pest management to optimize final yield and quality.