Sink strength, nutrient allocation, cannabinoid yield, and associated transcript profiles vary in two drug-type Cannabis chemovars.

Abstract

Cannabis sativa L. is one of the oldest domesticated crops. Hemp-type cultivars, which predominantly produce non-intoxicating cannabidiol (CBD), have been selected for their fast growth, seed, and fibre production, while drug-type chemovars were bred for high accumulation of tetrahydrocannabinol (THC). We investigated how the generation of CBD-dominant chemovars by introgression of hemp- into drug-type Cannabis impacted plant performance. The THC-dominant chemovar showed superior sink strength, higher flower biomass, and demand-driven control of nutrient uptake. By contrast, the CBD-dominant chemovar hyperaccumulated phosphate in sink organs leading to reduced carbon and nitrogen assimilation in leaves, which limited flower biomass and cannabinoid yield. RNA-seq analyses determined organ- and chemovar-specific differences in expression of genes associated with nitrate and phosphate homeostasis as well as growth-regulating transcription factors that were correlated with measured traits. Among these were genes positively selected for during Cannabis domestication encoding an inhibitor of the phosphate starvation response, SPX DOMAIN GENE3, nitrate reductase, and two nitrate transporters. Altered nutrient sensing, acquisition, or distribution are likely a consequence of adaption to growth on marginal, low-nutrient-input lands in hemp. Our data provide evidence that such ancestral traits may become detrimental for female flower development and consequently overall CBD yield in protected cropping environments.