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  • Author or Editor: Melissa Moher x
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The majority of commercial Cannabis sativa L. (cannabis) cultivators use a 12.0-hour uninterrupted dark period to induce flowering; however, scientific information to prove this is the optimal dark period for all genotypes is lacking. Knowing genotype-specific photoperiods may help to promote growth by providing the optimal photoperiod for photosynthesis. To determine whether the floral initiation of cannabis explants respond to varied photoperiods in vitro, explants were grown under one of six photoperiod treatments: 12.0, 13.2, 13.8, 14.4, 15.0, and 16.0 hours per day for 4 weeks. The percentage of flowering explants was highest under 12.0- and 13.2-hour treatments. There were no treatment effects on the fresh weight, final height, and growth index. Based on the results, it is recommended that an uninterrupted dark period of at least 10.8 hours (i.e., 13.2-hour photoperiod) be used to induce flowering for the ‘802’ genotype. In vitro flowering could provide a unique and high-throughput approach to study floral/seed development and secondary metabolism in cannabis under highly controlled conditions. Further research should determine if this response is the same on the whole-plant level.

Open Access

Until recently, most clonal cannabis (Cannabis sativa) has been propagated using fluorescent lights. Transitioning to light-emitting diodes (LEDs) may be a viable alternative to fluorescent lighting, enabling cultivators to provide specific spectrum treatments to enhance rooting while also saving energy. Vegetative stem cuttings of ‘Gelato-27’, ‘Grace’, and ‘Meridian’ were rooted for 15 days under various combinations of blue (B), red (R), ultraviolet-A (UVA) LEDs, phosphor-converted white (W) LEDs, and a fluorescent (F) control treatment, each with a canopy-level photosynthetic photon flux density (PPFD) of 200 µmol·m−2·s−1 and 16-hour photoperiod. The photon flux ratios of blue (B; 400–500 nm) and red (R; 600–700 nm) narrowband LED treatment combinations were (1) BR, fixed spectrum of B15:R85; (2) B, B75:R25 on day 0–2 followed by B15:R85 on day 2–14; (3) B+UVA, B75:R25 on day 0–2 followed by B15:R85 on day 2–14 plus 15 µmol·m−2·s−1 of UVA on day 7–14; (4) B50, B15:R85 on day 0–7 followed by B50:R50 on day 7–14. The W and F treatments both had static spectra. After the propagation period (i.e., plug stage), a portion of the cuttings under each treatment × cultivar combination were destructively harvested and the remainder were transplanted and grown vegetatively for an additional 21 days (i.e., transplant stage) under a PPFD of ≈275 µmol·m−2·s−1 from ceramic metal halide fixtures and then destructively harvested. Although there were no spectrum treatment effects on the percentage of cuttings that rooted, root index values were higher in cuttings grown under B+UVA vs. F. Further, relative root dry weights of plugs from the B, B+UVA, B50, and F treatments were higher than the W treatment. At the end of the plug stage, there were no spectrum treatment effects on the chlorophyll content index, cuttings grown under the B treatment had thicker stems compared with BR and W treatments, and cuttings grown under the F treatment exhibited the lowest percentage of new aboveground growth. None of the aforementioned spectrum treatment effects from the propagation stage persisted post-transplant. The use of LEDs is a promising, energy-efficient alternative to fluorescent lighting for cannabis propagation and B-enhanced spectrum treatments appear to enhance the rooting performance of clonal cannabis cuttings.

Open Access