Effect of Light Intensity on Photosynthetic Characteristics of High Δ9-THC Yielding Varieties of Cannabis sativa L.
Cannabis sativa L. (Cannabaceae), an annual herb is the natural source of cannabinoids that mainly accumulate in glandular trichomes of the plant. Due to the allogamous (cross fertilization) nature of Cannabis sativa it is very difficult to maintain the efficacy of selected high THC yielding elite varieties if grown from seeds under field conditions. Thus, the indoor cultivation, under controlled environmental conditions, using vegetative propagation of selected high yielding female clones can be a better alternative for its mass propagation. In the present study, plants of four drug type Cannabis varieties namely HPM, MX, K2 and W1 were grown indoors, under controlled environmental conditions (25±3°C, 55±5% RH and ˜ 700±24µmol m–2s–1 light at plant canopy level). Gas and water vapor characteristics of these plants were studied at different Photosynthetic Photon Flux Density (PPFD; 000, 500, 1000, 1500 and 2000µmol m–2s–1) for their efficient indoor cultivation. An increasing trend in photosynthesis (PN), transpiration (Tr) and stomatal conductance (gCO2) was observed with increase in PPFD up to 2000µmol m–2s–1 in all the varieties at optimum growth temperature (25±3°C). However, the magnitude of increase and maximum rate of PN (PN max) varied with the varieties. Highest rate of photosynthesis was observed in W1 followed by MX, K2 and HPM. Water Use efficiency (WUE) in W1, MX and HPM increased with light up to highest level tested, whereas, in K2 highest WUE was observed at 1500µmol m–2s–1. Our results show that this species is able to use high level of PPFD for its PN and therefore, may be cultivated in under bright indoor light (˜1500 to 2000µmol m–2s–1) for better growth and biomass. The strict control of other environmental factors however, should be maintained for a higher yield. Acknowledgment: This work was supported with federal funds from the National Institute of Drug Abuse (NIDA), National Institute of Health (NIH), Department of Health and Human Services, USA, under the contract No. N01DA-7–7746.