Flowering of the Orchid Miltoniopsis Augres ‘Trinity’ is Influenced by Photoperiod and Temperature Roberto G. Lopez, Erik S. Runkle and Royal D. Heins Department of Horticulture, Michigan State University East Lansing, Michigan 48824 USA Keywords: pansy orchid, potted flowering orchids, vernalization Abstract The production of flowering potted orchids has increased dramatically throughout the world in the past decade. For example, production value in the United States has increased 147% in the past six years, and in 2002 the estimated wholesale value was $105 million. Scheduling orchid species to flower on specific dates requires knowledge of how environmental parameters regulate plant development from propagation to flowering. In a preliminary experiment, we observed that flowering of Miltoniopsis Augres ‘Trinity’ was promoted by cool temperatures (14 to 20 o C), short photoperiods (9 hours), or a combination of both. We performed additional experiments to determine the minimum durations of short photoperiods and cool temperatures (vernalization at 14 ºC) required for rapid and uniform flowering. To quantify the effect of photoperiod before exposure to cool temperature, Miltoniopsis were placed under 9- or 16-h photoperiods at 20 ºC for 0, 4, 8, 12, or 16 weeks, then were transferred to growth chambers at 14 °C with a 9-h photoperiod for 8 weeks. To determine the optimal cooling duration, a separate experiment was performed in which plants were placed under 9- or 16-h photoperiods at 20 ºC for 8 weeks and then transferred to 14 °C with a 9-h photoperiod for 0, 3, 6, 9, or 12 weeks. Following treatments, plants were grown in a common environment at 20 °C with a 16-h photoperiod. The flowering percentage of plants that were not exposed to short days was only 40%. Flowering percentage was greatest when exposed to short days for 4 to 8 weeks before cooling. The optimum vernalization treatment was for eight weeks under short days. INTRODUCTION Orchids have become the second most valuable flowering potted crop in the United States (USDA, 2003). According to the American Orchid Society, over 75% of all orchids sold in the United States are Phalaenopsis, commonly known as the moth orchid (Griesbach, 2002). Currently, the wholesale price of flowering Phalaenopsis in a 15-cm pot in the U.S. is $8 to $12, with a retail price of $15 to $25 on the mass market (Wang, 2003). As the market becomes saturated with Phalaenopsis due to the widespread knowledge of its flower induction requirements, the price will likely decrease and the plant may become a commodity. Consequently, commercial growers and retailers are already seeking other orchids that have consumer appeal and can be programmed into flower for specific markets dates. Miltoniopsis, or the pansy orchid, produces inflorescences that are adorned with three to six flat, and large (7 cm) fragrant and showy flowers, which range in color from cream to pink, magenta, scarlet, or yellow. The flowers often last on the plant for four to eight weeks at temperatures from 14 to 20 ºC (Robinson, 2002). Due to these attributes, Miltoniopsis has become the fifth most valuable potted orchid produced commercially in the Netherlands, with 797,000 pots sold in 2001 (Barendse, 2002). In its native habitat, Miltoniopsis is an epiphytic and lithophytic genus of six species distributed throughout the wet cloud forest regions (610 to 2,100 m) from Costa Rica to Peru (Baker and Baker, 1993; Morrison, 2000). The sympodial growth habit of this compact plant is distinguished from Miltonia by the presence of a single leaf at the 175 Proc. V th IS on New Flor. Crops Eds.: A.F.C. Tombolato and G.M. Dias-Tagliacozzo Acta Hort. 683, ISHS 2005