TEMPERATURE AND PHOTOPERIODIC EFFECTS ON GROWTH AND FLOWERING OF ZYGOPETALUM REDVALE 'FIRE KISS' ORCHIDS

Flowering potted orchids have become the second most valuable floriculture flowering potted crop in the United States. However, little or no quantitative information exists on the flowering process of the majority of orchid species. We performed experiments to determine how temperature and photoperiod influence leaf development and flower induction of Zygopetalum Redvale ‘Fire Kiss’. In the first experiment, plants were placed under photoperiods ranging from 10 to 24 h of continuous light or 9 h with a 4-h night interruption (NI). Sixty percent to 80% flowered when grown under every photoperiod except continual (24 h) light, and flowering was slightly hastened under photoperiods ≤14 h. In a separate experiment, plants were placed into environmental chambers with constant temperatures of 14, 17, 20, 23, 26 and 29 °C and 9-h photoperiods with or without a 4-h NI. Plants developed nodes faster as temperature increased from 14 to 26 ^oC; after 15 weeks, plants at 14 ^oC had developed an average of only 1.8 new nodes, while those at 26 ^oC had developed an average of 4.8. In the third experiment, plants were placed under 9- or 16-h pre-cooling photoperiods for 8 weeks, then were transferred to cooling temperatures of 11, 14, 17, 20, and 23 ºC with 9- and 16-h photoperiods for 8 weeks. Plants grown under a 9-h pre-cooling photoperiod and then transferred to 11 or 14 ^oC had the highest flowering percentages and reached visible inflorescence in 17 to 22 days. Collectively, these studies indicate that Zygopetalum without a low temperature treatment is a quantitative short day plant. The most rapid, complete, and uniform flowering occurred when plants were grown under short days and then subjected to temperatures of 11 to 14 ^oC.

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