Date of Award
8-2024
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Plant and Environmental Science
Committee Chair/Advisor
James E Faust
Committee Member
Jeffrey Adelberg
Committee Member
Roberto Lopez
Abstract
Commercial propagators have reported relatively poor propagation success, e.g., <75% rooting, for many hemp (Cannabis sativa) cultivars. These rooting percentages have a significant economic impact due to the wasted labor, space and supplies. Also, the market demands 100% of the propagation cells in a tray to be fully rooted, thus repairing and replacing poorly rooted or unrooted cuttings requires significant labor cost. The goal of this thesis was to evaluate several factors that influence adventitious root formation of hemp stem cuttings.
Chapter 2 describes an experiment conducted to identify rooting hormone treatments that could improve propagation success. Sixteen combinations of indole-3-butyric acid (IBA; 0, 2000, 4000 and 6000 mg.L-1) and naphthalene acetic acid (NAA; 0, 2000, 4000 and 6000 mg.L-1) were evaluated for their effect on adventitious root formation on three floral hemp cultivars (THM Jack, Peach Haze, Sunset). Auxin treatments were applied as a basal stem dip into a liquid treatment for 5 s prior to planting. Cuttings were maintained under intermittent mist for 14 d then evaluated for root fresh weight, rooting percentage, and shoot fresh weight. ‘THM Jack’ had a combined greater root fresh weight and rooting percentage when treated with 4000 mg.L-1 IBA combined with 2000 or 4000 mg.L-1 NAA. ‘Peach Haze’ developed greater root fresh weight and rooting percentages when treated with 6000 mg.L-1 IBA combined with 4000 mg.L-1 NAA or 2000 mg.L-1 IBA combined with 6000 mg.L-1 NAA. ‘Sunset’ rooted optimally when treated with 4000 mg.L-1 NAA alone. These results demonstrate that auxin was beneficial for all three cultivars; however, the optimal auxin treatments are cultivar specific.
Hemp growers have reported reduced rooting success when cuttings are propagated under mist compared to humidity domes. Propagation substrates can become saturated when mist is not properly managed, which limits the oxygen necessary for adventitious root formation. In Chapter 3, an experiment was conducted to study the effects of volumetric water content (VWC) and volumetric air content (VAC) of a propagation substrate on rooting success of hemp. An easy-to-root cultivar of floral hemp (Sunset) was propagated in a peat-based substrate providing container capacities (CC) of 70%, 80%, 90% or 100%, which corresponded to 60%, 67%, 73% or 80% VWC and 32%, 25%, 19% or 12% VAC, respectively. Root fresh weight increased linearly from 0.39 to 0.60 g/cutting as VWC increased from 60% to 80%. Shoot fresh weight also increased linearly from 1.53 to 1.70 g/cutting as VWC increased from 60% to 80%. Rooting percentages averaged 98% across all VWC and VAC treatments. These results demonstrate that stem cuttings of floral hemp root well in peat-based substrates with a VWC of 73%-80% and VAC of 12%-19%.
Water management is essential to maintain nutrition status in propagation. When cuttings are maintained under intermittent mist, there is a greater risk of leaching nutrients from the media. In Chapter 4, experiments were conducted to identify the effect of fertilizer concentration applied to stock plants and to cuttings in propagation on adventitious root formation of two floral hemp cultivars (Cannabis sativa ‘THM Jack’ and ‘Peach Haze’). Stock plants were fertigated with a water-soluble fertilizer at low (100 mg.L-1 N), moderate (200 mg.L-1 N), or high (300 mg.L-1 N) concentrations. The harvested cuttings were then propagated in a peat-based substrate irrigated with no nutrients, low (100 mg.L-1 N) or moderate (200 mg.L-1 N) concentrations of the same water-soluble fertilizer. Therefore, three fertilizer treatments were provided to the stock plants followed by three fertilizer treatments provided during cutting propagation resulting in a 3 × 3 factorial arrangement. Cutting root and shoot fresh weight and rooting percentages were recorded, and tissue samples were collected for nutrient analysis to observe changes in nutrient concentrations of cuttings during 14 d in propagation. Cuttings of ‘THM Jack’ produced optimal root fresh weight (0.24 g/cutting) and rooting percentage (97%) when stock plants were fertilized at a moderate concentration followed by a low concentration of fertilizer applied in propagation. Cuttings of ‘Peach Haze’ produced optimal root fresh weight (0.16 g/cutting) and rooting percentage (90%) when a moderate concentration of fertilizer was applied to cuttings in propagation, while stock plant fertilization treatment had no effect. Shoot fresh weight increased as fertilizer concentrations increased in stock and propagation treatments. Tissue nutrient concentration of ‘THM Jack’ decreased after 14 d in propagation, e.g., N concentrations on Day 0 were 5.5% and decrease to 3.6% after 14 days. Cuttings that were fertigated with low and moderate fertilizer treatments in propagation had a smaller reduction in nutrient concentration compared to cuttings that received no fertilizer. For example, cuttings harvested from stock plants had a Mg concentration of 0.4% on Day 0 that decreased to 0.2%, 0.3%, and 0.3% when treated with no nutrients, low or moderate fertilizer concentration in propagation. In summary, cuttings of ‘THM Jack’ had an optimal combination of root fresh weight and rooting percentage when stock plants were irrigated with low to moderate fertilizer and low fertilizer was applied during the first 14 d of propagation. Cuttings of ‘Peach Haze’ had the greatest root fresh weight and rooting percentage when cuttings were irrigated with moderate fertilizer in propagation, while stock plant treatment did not have a significant effect on rooting.
In conclusion, we believe that hemp propagation can be improved by utilizing the correct formulation and concentration of rooting hormone, maintaining adequate moisture levels in the substrate while avoiding excessive misting, and applying nutrients in propagation. Phenotypes of hemp cultivars vary greatly. Growers should consider that the optimal treatments in our studies may not be representative across all cultivars.
Recommended Citation
Carver, Alexandra, "Factors Influencing Adventitious Root Formation Of Floral Hemp in Propagation" (2024). All Theses. 4354.
https://open.clemson.edu/all_theses/4354