Temperature and Pseudobulb Size Influence Flowering of Odontioda Orchids

Odontioda is a cool-growing, sympodial epiphytic genus of orchids originating from the Andes Mountains of South America. Several hybrids are commercially grown as potted flowering plants for their brightly colored flowers and compact growth habit. We quantified how constant and fluctuating day/night temperatures influenced inflorescence initiation, time from visible inflorescence (VI) to flower, and pseudobulb development. Odontioda George McMahon 'Fortuna' and Lovely Penguin 'Emperor' were grown at constant temperature set points of 14, 17, 20, 23, 26, or 29 °C and day/night (12 h/12 h) temperatures of 20/14, 23/17, 26/14, 26/20, 29/23, or 29/17 °C. Plants were grown in glass greenhouses under a 12-h photoperiod and a maximum irradiance of 500 micromol·m-2·s-1. Within 6 weeks, heat stress symptoms such as leaf necrosis were observed on plants grown at a day temperature of 26 °C or greater regardless of the night temperature. After 20 weeks, 90% or greater of both clones had a VI when grown at a constant temperature of 14 or 17 °C. Plants grown at a constant temperature of 17 °C had the greatest pseudobulb diameter with a mean increase of 3.5 to 4.0 cm. In all treatments, a minimum pseudobulb diameter was required for uniform inflorescence initiation; pseudobulbs with a diameter of 5.5 cm or greater developed a VI in 93% of plants. Data for time from VI to open flower were converted to a rate, and a thermal-time model relating temperature with inflorescence development was developed. The base temperature and thermal time for VI to flower in George McMahon 'Fortuna' and Lovely Penguin 'Emperor' were estimated at -0.1 °C and 1429 °C·d-1 and 0.8 °C and 1250 °C·d-1, respectively. This information could be used by commercial orchid growers to assist in producing potted flowering Odontioda orchids for specific market dates.