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  • Author or Editor: Lillian N. Borbas x
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Micropropagation of hemp (Cannabis sativa) is constrained by problems with hyperhydricity and culture decline of microshoots. These problems can be reduced by increasing agar and nutrients in the media during micropropagation stages 1 and 2, respectfully. Performance of microshoots of ‘Abacus’ and ‘Wife’ hemp cultured in Driver and Kuniyuki Walnut medium (DKW) for 15 weeks (6 weeks of stage 1 + 9 weeks of stage 2), with subculturing every 3 weeks during both stages 1 and 2, or in Murashige and Skoog with vitamins medium (MS) for 6 weeks (stage 1) followed by Lubell-Brand Cannabis medium (LBC) for 9 weeks (stage 2), with subculturing every 3 weeks during both stages 1 and 2, was evaluated. In a separate study, microshoot performance of ‘Abacus’ and ‘Wife’ in MS for 3 weeks (stage 1) followed by LBC for 6 weeks (stage 2), with subculturing every 3 weeks, using boxes (Magenta GA-7) with lids featuring a vent with a diameter of 10 mm and a pore size of 0.2 µM or using microboxes (Sac O2 O95/114 + OD95) with lids featuring a filter (Sac O2 #10) were evaluated. Shoot multiplication rate (SMR) and explant height were greater for ‘Abacus’ in LBC than DKW. For ‘Wife’, SMR at 9 weeks was greater in LBC, as LBC provided more nutrients and water than cultures had received in MS initially during stage 1. Culture medium did not influence ex vitro rooting success, which was 75% for ‘Abacus’ and ≥ 90% for ‘Wife’. Microboxes resulted in greater hyperhydricity of shoots and a lower ex vitro rooting percentage than boxes. For cultivars that are highly prone to developing hyperhydricity, like ‘Abacus’, the microboxes were not adequate to control this condition.

Open Access

There is demand for micropropagated Cannabis sativa liner plants, because they are uniform, vigorous, and pathogen free; however, availability is limited because of challenges with in vitro culture decline and ex vitro rooting. Ex vitro rooting success of microcuttings was evaluated for ‘Abacus’ and ‘Wife’ when cultures were 6, 9, 12, 15, and 18 weeks old from initiation. Microcuttings of ‘Wife’ harvested from 6, 9, and 12-week-old cultures rooted at or above 80%, but rooting declined to 50% and 30% for 15- and 18-week-old cultures, respectively. Rooting for ‘Abacus’ remained relatively constant between 47% and 70% for microcuttings harvested from 6- to 18-week-old cultures. ‘Wife’ plants grown from microcuttings, stem cuttings, and retip cuttings (cuttings taken from new shoots on recently micropropagated plants) had equivalent total shoot length, number of shoots, and flower dry weight, whereas micropropagated ‘Abacus’ plants had less shoot length and flower dry weight than plants from stem cuttings. However, when micropropagated ‘Abacus’ plants were provided an extra week of vegetative growth to reach an initial size equivalent to stem and retip plants, all plants performed the same. Propagation method did not change cannabinoid content for both ‘Abacus’ and ‘Wife’. Retip cuttings of ‘Abacus’ and ‘Wife’ rooted at 76% to 81% without rooting hormone, which is comparable to rates reported for stem cuttings of C. sativa treated with rooting hormone. Propagators should consider retipping to expand their liner production, because retips root well and possess the same desirable attributes as micropropagated plants.

Open Access