Abstract
Apical stem cuttings are the primary method for propagation in medicinal cannabis, yet propagation has not been studied as extensively as the later stages of crop cultivation. This study examined how mother plant age and photosynthetic photon flux density (PPFD) during mother plant cultivation and propagation affect rooting, growth, and development of apical stem cuttings. Mother plants (Cannabis sativa ‘Original Blitz’ and ‘King Harmony’) were grown in climate-controlled chambers under two light intensities (400 and 800 μmol·m−2·s−1) for up to 6 months. Apical stem cuttings were excised every 3 weeks and subsequently propagated without externally applied auxin for 3 weeks under three light intensities (50, 150, and 250 μmol·m−2·s−1). Mother plant age did not affect rooting (root dry mass and fraction of rooted cuttings). However, older mother plants exhibited decreased cutting dry mass at severance, which coincided with a reduced leaf area. The light intensity during mother plant cultivation had genotype-specific effects, with rooting either reduced or unaffected for the higher light intensity. This reduction coincided with an accumulation of starch and soluble sugar at the stem base at severance, while auxin concentrations in the apex, leaf, and stem base were unaffected by light intensity during mother plant cultivation. In contrast, light intensity during propagation did not affect the fraction of rooted cuttings. However, higher light intensity increased root and cutting dry mass. These findings indicate that mother plant age, up to 6 months, does not impact rooting in stem cuttings. However, higher light intensity during mother plant cultivation reduced rooting genotype-dependently, whereas higher light intensity during propagation increased root dry mass without affecting fraction of rooted cuttings.
