Physical factors increased quantity and quality of micropropagated shoots of Cannabis sativa L. in a repeated harvest system with ex vitro rooting

Abstract

Micropropagation is a preferred method to propagate clean, clonal stock plants. Subculture is labor intensive and costly. In vitro hedging can reduce hood labor and was demonstrated with cannabis (Cannabis sativa L. ‘US Nursery Cherry 1’) using both apical and nodal explants at four different photosynthetic photon flux densities (25–167 μmol m−2 s−1) in vessels with vented or non-vented closures. The numbers of harvested shoot tips from four repeated 3-wk cutting cycles without subculture and the quality of the harvested shoot tips during ex vitro rooting in phenolic foam plugs were observed. The number of shoot tips harvested in non-vented vessels increased over four repeated cycles; however, there was a decline in number of shoot tips harvested from vented vessels in the fourth cycle due to excessive drying and collapse of the agar matric. The number of shoot tips harvested through repeated cycles was increased with light intensity. Nearly 100% of the micro-cuttings from optimal light and ventilation rooted ex vitro. Most plantlets had roots that penetrated the exterior surfaces of the plug after 2 wk. The number of leaves per rooted plantlet ex vitro increased with light intensity in vitro. Micropropagation labor efficiency could be improved by using a multi-cycle cutting process which would allow the same material to be repeatedly cut from rooted bases instead of subcultured. In a system with strong apical dominance, enhanced axillary divisions of shoot tip explants over successive cycles of cutting, without the need of exogenous PGRs, were further increased by appropriate in vitro factors, light, and ventilation, presenting labor saving potential compared to standard, single-cut system in common use.