A One-Step Grafting Methodology Can Adjust Stem Morphology and Increase THCA Yield in Medicinal Cannabis

Abstract

The standard two-step methods for grafting horticultural crops involve cultivating the rootstock for a period of time and then connecting the scion. Medicinal Cannabis differs from most annual horticultural crops because it is usually clonally propagated from cuttings. We developed a grafting methodology specifically for medicinal Cannabis, involving a single step, in which a freshly cut scion is grafted to a freshly cut donor stem that will become the rootstock. This study also aimed to uncover a potential role for roots in influencing cannabinoid content. Two varieties with desirable attributes but cultivation limitations were selected to act as scions. The first, “CBD1” was a high CBDA accumulating variety with low biomass yield, and the second, “THC2”, was a high yielding, high THCA accumulating line with inconsistent root development during cloning. Two candidate rootstocks, “THC9r” and “THC8r”, were identified; both were high THCA, low CBDA varieties. Biomass yields in the THC2 scions grafted to THC9 rootstocks (THC9r_2s) were 20% higher than in the non-grafted THC2 plants. In CBD1 grafted plants, the concentrations of CBDA and some minor cannabinoids were significantly different to non-grafted CBD1, but biomass yields were lower. There was a trend towards a higher concentration of THCA in THC9r_2s plants, and when combined with the increased biomass, yield of THCA was increased from 8 g Plant−1 to 13 g Plant−1. Our results present a new grafting method for medicinal Cannabis that improved yield in THC2 and required no additional cultivation time.