Photoperiod, irradiance, and temperature affect Echinopsis ‘Rose Quartz’ flowering

Photoperiod, irradiance, cool temperature (5 °C), and benzyladenine (BA) application effects on Echinopsis ‘Rose Quartz’ flowering were examined. Plants were placed in a 5 °C greenhouse under natural daylight (DL) for 0, 4, 8, or 12 weeks, then moved to a 22/18 °C (day/night temperature) greenhouse under short days (SD, 8-hour DL) plus 0, 25, 45, or 75 µmol·m^-2·s^-1 supplemental lighting (0800-1600 HR; 8-hour photoperiod), long days (LD) delivered with DL plus night-interruption lighting (NI) (2200-0200 HR), or DL plus 25, 45, or 75 µmol·m^-2·s^-1 supplemental lighting (0800-0200 HR) for 6 weeks. Plants were then grown under DL only. Percent flowering plants increased as irradiance increased from 0-25 to +75 µmol·m^-2·s^-1 on uncooled plants, from 0% to 100% as 5 °C exposure increased from 0 to 8 weeks under subsequent SD and from 25% to 100%as 5 °C exposure increased from 0 to 4 weeks under subsequent LD. As 5 °C exposure duration increased from 0 to 12 weeks (SD-grown) and from0 to 8 weeks (LD-grown), flower number increased from 0 to 11 and from 5 to 21 flowers per plant across irradiance treatments, respectively. Total production time ranged from 123 to 147 days on plants cooled from 8 to 12 weeks (SD-grown) and from 52 to 94 days on plants cooled for 0-4 weeks to 119-153 days on plants cooled for 8-12 weeks (LDgrown). Flower life varied from 1 to 3 days. BA spray application (10-40 mg·L^-1) once or twice after a 12-week 5 °C exposure reduced flower number. Flower development was not photoperiodic. High flower number (17-21 flowers/plant) and short production time (including cooling time, 120-122 days) occurred when plants were grown at 5 °C for 8 weeks, then grown under LD + 45-75 µmol·m^-2·s^-1 for 6 weeks (16 hours; 10.9- 12.8 mol·m^-2·d^-1) at a 22/18 °C day/night temperature. Taken together, Echinopsis ‘Rose Quartz’ exhibited a facultative cool temperature and facultative LD requirement for flowering.