Photoperiod, Irradiance, and Cool Temperature Effects on Gymnocalycium, Rebutia, Lobivia, and Sulcorebutia sp. Growth and Flowering

Abstract

A study was conducted to determine if photoperiod, irradiance, and/or a cool temperatures impacted flowering of selected species in five cactus genera. Gymnocalycium, Rebutia, Lobivia, and Sulcorebutia plants were grown for 4 months under natural daylight conditions (August–November) in a greenhouse maintained at 26 ± 2 °C. Plants were then placed in either of two greenhouses: 1) a greenhouse maintained at 22 °C day/18 ± 1 °C night temperature with an 8-h daylength (SD) or natural daylight plus night interruption lighting (NI; 2200–0200 HR), or 2) a greenhouse maintained at 5 ± 2 °C under natural daylight conditions (8–10 h). After 12 weeks at 5 °C, plants were moved to the SD and NI lighting treatments in the before mentioned greenhouse and additional lighting treatment [natural daylight plus supplemental high-pressure sodium lighting (85–95 μmol·m-2·s-1; 0800–0200 HR)]. In all cases, plants were moved out of lighting treatments after 6 weeks and were then grown under natural daylight conditions in a greenhouse maintained at constant 22 ± 1 °C. Data were collected on the approximate date growth commenced, the date when each flower opened (five flowers only), flower number per plant, and individual flower longevity (five flowers only). Species were classified into photoperiodic and irradiance response groups where appropriate and whether species exhibited a vernalization requirement was reported. Lastly, whether dormancy occurred and what conditions overcame that dormancy was reported.