RESUMO
BACKGROUND: Cryopreservation is the only method allowing the safe and cost-effective long-term conservation of important germplasm. Recent use of the cryo-plate system has proven beneficial in further simplifying the cryopreservation protocols. OBJECTIVE: Developing an efficient protocol for the cryopreservation of axillary buds of Cannabis sativa elite cultivars (MX and V1-20) by the V-cryoplate droplet-vitrification technique. MATERIALS AND METHODS: Stem segments (~5 cm in length) with mature axillary buds collected from indoor-grown plants were surface sterilized and then either precultured on MS basal medium with 0.1 M sucrose (1st step preculture) for 72 h or non-precultured. All mature axillary buds (~1 mm) were aseptically excised from stem segments and precultured for an additional 48 h on MS basal medium with sucrose (0.3 M) and 5% DMSO prior to cryopreservation (2nd step preculture). Biomass samples of fully mature mother plants and regrown cryopreserved plants were analyzed for Δ9-THC and CBD content using gas chromatography-flame ionization detector (GC/FID). RESULTS: The survival and regrowth rates of cryopreserved axillary buds of cultivar MX following this two-step preculture were 45% and 42% respectively, while those of cultivar V1-20 were 47% and 44% respectively. A direct preculture of axillary buds (2nd step preculture) on high sucrose (0.3M sucrose) significantly decreased both the survival and regrowth levels of axillary buds of cultivar MX (5% and 3% respectively) as well as those of cultivar V1-20 (20% and 17% respectively). Δ9-THC and CBD content of mother plants and regrown cryopreserved plants were found to be highly comparable to each other. CONCLUSION: The resulting plants after cryopreservation appeared normal without any callus formation or morphogenetic variation. On maturity, mother plants and re-grown cryopreserved plants were comparable in terms of Δ9-THC and CBD content. This report provides an efficient protocol for cryopreservation of axillary buds of Cannabis sativa cultivars which may be applicable to other important cultivars, plant parts and other related medicinal plants.