Elevated UV photon fluxes minimally affected cannabinoid concentration in a high-CBD cultivar

F Mitchell Westmoreland; Paul Kusuma; Bruce Bugbee

doi:10.3389/fpls.2023.1220585

Elevated UV photon fluxes minimally affected cannabinoid concentration in a high-CBD cultivar

Front Plant Sci. 2023 Aug 11:14:1220585. doi: 10.3389/fpls.2023.1220585. eCollection 2023.

Authors

F Mitchell Westmoreland¹, Paul Kusuma^{1

2}, Bruce Bugbee¹

Affiliations

¹ Department of Plants, Soils and Climate, Crop Physiology Laboratory, Utah State University, Logan, UT, United States.
² Department of Plant Sciences, Horticulture and Product Physiology, Wageningen University & Research, Wageningen, Netherlands.

Abstract

Ultraviolet photons (UV) can damage critical biochemical processes. Plants synthesize photo-protective pigments that absorb UV to minimize damage. Cannabinoids absorb UV, so increased UV has the potential to increase cannabinoid synthesis. Studies in the 1980's provided some evidence for this hypothesis in low-cannabinoid cultivars, but recent studies did not find an increase in cannabinoid synthesis with increasing UV in high-cannabinoid cultivars. These studies used low UV photon fluxes, so we examined the effect of higher UV photon fluxes. We used fluorescent UV lights with 55% UV-B (280 to 314 nm) and 45% UV-A (315 to 399 nm). Treatments began three weeks after the start of short days and continued for five weeks until harvest. Established weighting factors were used to calculate the daily biologically effective UV photon flux (UV-PFD_BE; 280 to 399 nm). Daily UV-PFD_BE levels were 0, 0.02, 0.05, and 0.11 mol m^-2 d^-1 with a background daily light integral (DLI) of 30 mol m^-2 d^-1. This provided a ratio of daily UV-PFD_BE to DLI of 41 to 218% of summer sunlight in the field. Cannabinoid concentration was 3 to 13% higher than the control in UV treated plants, but the effect was not statistically significant. Fv/Fm and flower yield were reduced only in the highest UV treatment. These data support recent literature and lead us to conclude that an elevated flux of UV photons is not an effective approach to increase cannabinoid concentration in high-cannabinoid cultivars.

Keywords: UV; cannabinoids; cannabis; photo-protective pigments; specialized metabolism; ultraviolet photons.

Grants and funding

This study received funding from Utah Agricultural Experiment Station, SunMed Growers, METER Group Inc. and Statehouse. The funders were not involved in the study design, collection, analysis, interpretation of data, the writing of this article or the decision to submit it for publication. Approved as UAES Journal paper number 9685.