Page 13 - CSHS 2022 Book of Abstracts - 2022-08-22 web version

CSHS 2022 Conference

Abstracts – Oral Presentations

(CO.1) Twelve-Hour Photoperiod Is Not Optimal for Inducing Flowering in All Drug-Type
Cannabis sativa Cultivars
Ashleigh Ahrens*, David Llewellyn, Youbin Zheng
Department of Environmental Sciences, University of Guelph, Guelph, ON
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Cannabis sativa is a valuable recent addition to Canada’s economy with the legalization for recreational use in 2018.
Currently, the vast majority of controlled environment cannabis cultivators are using 12h light/12h dark to induce
flowering. To test the hypothesis that some drug-type cannabis cultivars can flower under photoperiods longer than
12h, young clones of ten cannabis cultivars were grown under six photoperiod treatments (all on a standard 24-h
day): 12, 12.5, 13, 13.5, 14, 15, for 3-4 weeks in a growth chamber at 25°C under photosynthetic photon flux density
≈300 µmol·m-2·s-1 provided by LEDs. While longer photoperiods extended the time to the appearance of visible
flowers for some of the cultivars, the delay was normally only about 2 days. No flowers on plants under 15h matured
beyond the initiation phase. At the time of harvest, flower biomass metrics generally responded quadratically with
increasing photoperiod, with the vertices for individual parameters depending on the different cultivars. These
results suggest that the industry-standard 12h photoperiod may not be optimal for all cultivars, as some cultivars
can have a strong flowering response under longer photoperiods such as 13h. Growers should test their cultivars to
determine the optimal photoperiod for producing inflorescence biomass.

(CO.2) Comparison of four spectra delivered as intra-canopy lighting in Cannabis flower
production
Brian Poel, David Hawley*
Fluence, Austin, TX, USA
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In conventional cannabis (Cannabis sativa L.) production, whether in a greenhouse or sole-source indoor conditions,
photosynthetic light is most commonly added as toplighting—light from high-powered fixtures mounted above the
crop. A growing body of research has shown that dry floral yields of cannabis continue to increase beyond
conventional toplight intensities of 800-1000 µmol·m-2·s-1 up to 1800 µmol·m-2·s-1. In other high-density
commercial crops such as tomato and cucumber, increasing total light intensity incident on a crop canopy via intra-
canopy lighting (ICL) can further increase yields compared to increasing total light intensity via toplighting alone.
While toplight spectrum can have a significant effect on yield and secondary metabolism, it is possible that the same
spectral responses may not be conserved when delivered via ICL. Therefore, researchers evaluated the effect of four
ICL spectra at 566 µmol·s-1 delivered with a broad spectrum toplight intensity of 1200 µmol·m-2·s-1 for 12h·d-1 to
five-week old Type-I chemotype ‘Blue Dream’ plants for 56 days. At harvest, treated plants were measured for
height, inflorescence size, and total fresh mass per plant, dried to approximately 10% moisture content and
measured for total floral mass per plant. Additionally, tissue from plants of under individual treatments was batched
and analyzed for concentration of 10 cannabinoids and 21 terpene species. While total plant biomass was similar
among ICL treatments, optimal ICL spectrum should integrate a range of factors, such as ICL efficacy, uniformity
(both metabolite and morphology) and labour considerations. Therefore, a discussion on these as well as economic
considerations will also be presented.

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