Photoperiodic responses of Cannabis sativa: developmental and molecular aspects

Abstract

The timing of reproductive development is influenced by photoperiod (daylength) in many plants, including Cannabis sativa. However, the developmental and molecular details and the variability of photoperiodic responses in C. sativa are not well understood. I evaluated the photoperiod sensitivity of four high-CBD drug-type Cannabis varieties for four stages of reproductive development by comparing the timing of each stage between plants that received different periods of long-day (LD) exposure prior to the short-day (SD) treatment. In addition, I looked at the influence of photoperiod on the duration between different stages of development, and the effect of plant age on photoperiod sensitivity. The timing of each stage, including the induction of solitary flowers and anthesis was accelerated in 'Eden' under SD conditions. 'Grape Indica' started developing inflorescences in 6 weeks under LD, but the process was also faster when SD treatment began earlier. The development of 'Auto Pivot', on the other hand, was slightly delayed under SD, but each stage occurred with a consistent number of leaves in all treatments. 'Russian Auto' had a shorter juvenile phase and showed accelerated inflorescence development under SD, but earlier stages were not accelerated even though SD development happened with fewer leaves at each stage. Also, older plants responded to SD slightly earlier, especially compared to plants directly started in SD. These results suggest there are important differences between C. sativa varieties in terms of the timing and the process of reproductive development, even within the day-neutral/auto-flowering varieties. I identified four FLOWERING LOCUS T (FT)-LIKE genes in the Cannabis genome and analyzed their diurnal expression patterns in 'Eden' and 'Auto Pivot' under LD and SD. FTL2 showed a similar expression pattern to FT genes that are known to induce flowering in other SD species, and the expression in photoperiod-sensitive variety, Eden, was different between photo-period treatments, while it was mostly unaffected in the day-neutral variety, Auto Pivot, suggesting FTL2 could be a potential photoperiod-regulated floral promoter in C. sativa.