Cannabis sativa is cultivated worldwide for diverse purposes ranging from fiber and seed oil to medical and recreational inflorescences rich in cannabinoids and terpenes. The architecture and timing of flowering directly determine yield, product quality, and propagation strategies. For hemp, flower onset influences fiber quality; for seed crops, inflorescence architecture affects seed numbers; and for medicinal cannabis, the inflorescence itself is the primary product. Despite its importance, the mechanisms linking photoperiod signals and hormone regulation in cannabis reproductive development remain unclear. Due to these gaps in understanding, there is a need to investigate how light regimes and phytohormones jointly regulate cannabis inflorescence formation.
In a study (DOI: 10.1093/hr/uhae245) published September 3, 2024, in Horticulture Research, researchers at the Agricultural Research Organization, The Volcani Institute (Israel), provide the most detailed account to date of how light and hormones jointly direct cannabis flowering. They found that continuous short-day exposure is required to initiate and sustain condensed inflorescences, while gibberellin (GA) levels determine whether flower clusters remain compact or stretch apart. The findings offer new insight into the delicate balance between environment and hormones in cannabis development.
The team cultivated cannabis plants under controlled long-day (LD, 18 h light/6 h dark) and short-day (SD, 12 h/12 h dark) regimes. Under LD, plants produced solitary flowers without developing inflorescences. By contrast, SD triggered inflorescence initiation within seven days, with condensed flower clusters forming after about two weeks. A minimum of three consecutive SD days was required to signal inflorescence initiation, but continuous SD was necessary to sustain development. Switching plants back to LD caused inflorescences to disassemble into solitary flowers through renewed internode elongation. Hormone analysis revealed that SD significantly reduced auxin and gibberellin (GA4) levels in shoot apices, correlating with shortened internodes and compact inflorescences. Conversely, returning plants to LD restored hormone levels, reversing inflorescence development. Exogenous GA applications mimicked LD responses even under SD, delaying or disrupting inflorescence formation and decreasing cannabinoid levels such as tetrahydrocannabinolic acid (THCA) and cannabidiol (CBD). In contrast, synthetic auxin treatments had little effect. These findings highlight GA as a critical mediator of photoperiod signaling in cannabis inflorescence tissues, linking environmental cues to both plant architecture and metabolite accumulation.
“Our results demonstrate that continuous short-day conditions are indispensable for stable cannabis inflorescence development,” said lead author Dr. Ben Spitzer-Rimon. “By revealing how GA levels govern the balance between compact and elongated plant structures, we provide a mechanistic link between environmental light cues and reproductive morphology. Importantly, we also show that GAs negatively influence cannabinoid accumulation, underscoring their dual role in shaping both architecture and product quality. These insights can inform breeding and cultivation strategies across industrial hemp, seed production, and medicinal cannabis sectors.”
This study advances understanding of cannabis reproductive biology with practical implications for agriculture and biotechnology. By manipulating light regimes and gibberellin signaling, growers can better control flowering schedules, optimize inflorescence architecture, and enhance yield consistency. For hemp producers, timing inflorescence onset could maximize fiber quality; for seed-oil cultivation, inflorescence architecture directly impacts seed set; and for medicinal cannabis, maintaining condensed inflorescences is vital for cannabinoid-rich harvests. Future research exploring cultivar variation and integrating hormone regulators may further refine cultivation practices, offering sustainable, targeted approaches to boost productivity and quality across cannabis industries.
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References
DOI
10.1093/hr/uhae245
Original Source URL
https://doi.org/10.1093/hr/uhae245
Funding information
The plant material (rooted cuttings) was supplied by Canndoc Ltd, a certified commercial cultivation producer in Israel. We are grateful for the cooperation and advice of Neri Barak, the founder and president of Canndoc Ltd. This work was supported by the Chief Scientist of the Israeli Ministry of Agriculture and Rural Development grant 20-01-0177.
About Horticulture Research
Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.