Effect of Explant Source on Phenotypic Changes of In Vitro Grown Cannabis Plantlets over Multiple Subcultures

SIMPLE SUMMARY: While micropropagation systems have been developed for cannabis, little attention has been given to the potential impact of explant source within the plant on subsequent growth and development in vitro. From other species, it is known that the explant source can have a significant impact on future development, presumably due to variations in endogenous phytohormones, sugars, and epigenetic state. This study was performed using a high-cannabinoid cultivar of cannabis, an economically important crop, to compare the growth and development of explants collected from various positions within the plant, ranging from the top to the bottom. Our results show that the multiplication rate (i.e., number of nodes), especially with explants derived from middle and apical parts of the mother plant, decreased over multiple subcultures, which can result from epigenetic machinery. In contrast, explants derived from the basal portion of the plant had an acceptable multiplication rate throughout the experiment and produced cannabis plantlets with shorter but wider leaves, indicative of rejuvenation. Hence, these results suggest that basal-derived cannabis explants should be used preferentially as starting material for in vitro propagation. ABSTRACT: Drug-type cannabis is often multiplied using micropropagation methods to produce genetically uniform and disease/insect-free crops. However, micropropagated plantlets often exhibit phenotypic variation, leading to culture decline over time. In cannabis, the source of these changes remains unknown, though several factors (e.g., explant’s sources and prolonged in vitro culture) can result in such phenotypical variations. The study presented herein evaluates the effects of explant sources (i.e., nodal segments derived from the basal, near-basal, middle, and apical parts of the greenhouse-grown mother plant) over multiple subcultures (4 subcultures during 235 days) on multiplication parameters and leaf morphological traits of in vitro cannabis plantlets. While initial in vitro responses were similar among explants sourced from different regions of the plant, there were significant differences in performance over the course of multiple subcultures. Specifically, explant source and/or the number of subcultures significantly impacted plantlet height, number of nodes, and canopy surface area. The explants derived from the basal and near-basal parts of the plant resulted in the tallest shoots with the greatest number of nodes, while the explants derived from the middle and apical regions led to shorter shoots with fewer nodes. Moreover, the basal-derived explants produced cannabis plantlets with shorter but wider leaves which demonstrated the potential of such explants for in vitro rejuvenation practices with minimal culture decline. This study provides new evidence into the long-term impacts of explant source in cannabis micropropagation.