Photoperiod and irradiance affect Monadenium coccineum Flowering

Monadenium coccineum (Pax.) is a succulent plant indigenous to Tanzania with potential as a new flowering potted plant.  Plants bloom with inconspicuous flowers, but have brightly colored red bracts surrounding flowers that are ornamental.  We determined how photoperiod and irradiance affected flowering to allow for production scheduling.  One hundred and twenty rooted cuttings (7–8 nodes) were grown under natural daylight +25 μmol·m^-2·s^-1 supplemental high-pressure sodium lighting (0800-0200HR; 22/18 °C day/night temperature) until Dec. 13 when plants were pruned to five nodes.  After two weeks, plants were placed under short days (SD, 8-h; covered from 1600–0800 HR), or long days (LD, 16-h).  Under both photoperiods, plants received  +0, +25, +50, or +100 μmol·m^-2·s^-1 supplemental lighting (high-pressure sodium lamps). The LD treatments were provided by providing night interruption lighting (2 μmol·m^-2·s^-1; 2200-0200HR (‘0’ irradiance treatment) or lighting from 0800–0200 HR.  After four weeks, three plants from each irradiance treatment (12 of 15 plants) under SD were moved to each irradiance treatment under LD, and vise versa.  Data were collected on time to anthesis, node number below the first flower, branch number, and flower number on one branch.  Plants flowered fastest under the continuous LD+100 μmol·m^-2·s^-1 treatment (41 d), or when moved from any of the SD treatments to the LD+100 μmol·m^-2·s^-1 treatment (44–49 d).  Plants that flowered fastest had the lowest node number below the first flower (1 leaf), 1.7 branches, 3–4 flowers per branch, and 6–7 total flowers.  Plants grown under continuous night interruption lighting and plants moved from SD+100 μmol·m^-2·s^-1 to night interruption lighting did not flower.  Also many plants moved from LD to ambient SD, as well as, plants grown under continuous ambient SD did not flower.  All plants flowered in the LD+25 μmol·m^-2·s^-1 moved to SD+100 μmol·m^-2·s^-1 treatment and the night interruption moved to SD+25 μmol·m^-2·s^-1 treatment, but they had the longest days to anthesis (82 d).   Plants with the greatest flower number (grown under continuous SD+25 μmol·m^-2·s^-1 treatment) had 19 flowers per plant, 6.3 flowers per branch, 3 branches, 3 leaves below the first flower, and flowered in 52 d.   Data here suggest that M. coccineum is a facultative LD plant, with a facultative irradiance response.