WUR Rooting Trials
Published on 10/01/2022
Introduction
The rapid development of the medicinal cannabis industry requires companies that continuously innovate their products and continuously acquire knowledge on crop cultivation, such as Grodan and Fluence by OSRAM. Scientists conducted a study with cultivators to gain further insights into how to improve stone wool substrates and lighting recipes for optimising medicinal cannabis propagation. Some interesting insights!
Cannabis Rooting Trials
Growers choose the cultivation system based on the plant’s end-use. The product’s value influences this choice and shapes the propagation approach. In greenhouse and indoor settings, growers treat cannabis as a horticultural crop and primarily propagate it through stem cuttings. Achieving uniform crop growth is crucial in cannabis production, as uneven growth can reduce both yield and inflorescence quality. When some cuttings root less effectively, they absorb less water and nutrients, slowing their growth. These smaller plants then struggle to compete for light, which further increases variation in plant size across the crop.
Most researchers have focused on optimizing the flowering phase of cannabis, often neglecting the propagation stage. From April to September 2021, Cultivators, Grodan, and Fluence by OSRAM partnered to conduct essential research at Wageningen University & Research. They structured the rooting trials as three separate experiments and carried them out in greenhouse compartments (Fig. 1).
Figure 1: experimental set-up
What is the effect of leaf area and cutting tray density on adventitious rooting and growth?
To prevent water stress, growers root stem cuttings in high-humidity environments and reduce leaf area to lower transpiration rates. However, leaves serve as sources of assimilates essential for successful rooting. Costa et al. (2002) demonstrated that the leaf area of rose cuttings can indicate growth potential. In their study, the root system size was directly proportional to the initial leaf area of the stem cuttings. Therefore, increasing leaf area and leaf number may enhance adventitious rooting success. On the other hand, reducing leaf number allows for higher cutting densities, which boosts production efficiency per unit of ground area. Changing the density within nursery trays has also influenced the microclimate and, in turn, altered cutting morphology—cuttings placed at higher densities developed longer stems with smaller leaf areas.
Alternatives to synthetic rooting supplements?
Auxins strongly influence plant processes like adventitious root formation and stem growth in various crops. Since some countries prohibit the use of synthetic auxins, there’s a growing demand for alternative rooting supplements. Hydrogen peroxide (H₂O₂) acts as a signaling molecule in the initiation and development of adventitious roots and may play a key role in lateral root formation. In this trial, we tested several rooting supplements as potential alternatives to synthetic auxins such as Clonex and Rhizopon. Clonex and H₂O₂ both promoted rooting and show promising potential. Although aloe vera powder contains salicylic acid, auxins, and gibberellins—which could support rooting—it did not promote rooting in this trial.
Furthermore, adventitious rooting also shows to be affected by light intensities. The trials have shown that higher light levels during the initial phase of propagation might inhibit adventitious root formation. Increasing light levels gradually during propagation might hold potential to enhance rooting and growth, in comparison to static light levels.
Additionally, the harvest time of cuttings has shown to affect rooting ability significantly. This stresses the importance of maintaining mother plants under stable climate and crop training techniques. It is hypothesized that maintaining mother plants with unstable conditions might result in variations in endogenous hormone and sugar levels, which subsequently could affect rooting ability.
Fluence by OSRAM and Cultivators are preparing to conduct a second round of rooting trials in 2022 to optimize cannabis propagation. Based on these findings further conclusions can be drawn from the 2021 trials.
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