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ISHS Acta Horticulturae 766: XXVII International Horticultural Congress - IHC2006: International Symposium on Ornamentals, Now!

EFFECT OF TEMPERATURE AND PSEUDOBULB MATURITY ON FLOWERING OF THE ORCHID MILTONIOPSIS AUGRES 'TRINITY'

Authors:   R.G. Lopez, E.S. Runkle
Keywords:   juvenility, pansy orchid, vernalization
DOI:   10.17660/ActaHortic.2008.766.35
Abstract:
Commercial production of the pansy orchid, Miltoniopsis, requires an understanding of how to regulate the flowering process. From previous research, we determined that flowering of Miltoniopsis Augres ‘Trinity’ was promoted most when plants were exposed to short days and then vernalized at 11 or 14°C for at least 8 weeks. Here, we quantified how constant and fluctuating day/night temperatures and pseudobulb maturity influenced time to visible inflorescence (VI) and time from VI to open flower. The diameters of three pseudobulbs were measured on each of 72 Miltoniopsis Augres ‘Trinity’ plants, then plants were vernalized in a growth chamber with a 12-h day/12-h night temperature setpoint of 16/14°C for 8 weeks. Plants were then forced in glass greenhouses under a 16-h photoperiod with constant temperatures of 14, 17, 20, or 23°C, or day/night temperatures (12h/12h) of 20/14 or 23/17°C. Only 27% of the pseudobulbs with a diameter ≤1.5 cm initiated flowers, whereas 90% of pseudobulbs with a diameter ≥3.1 cm became reproductive. Average time from the end of vernalization to appearance of the first VI was 89 and 8 days for plants with pseudobulb diameters ≤1.5 or ≥3.1 cm, respectively, regardless of forcing temperature. Average time from VI to flowering was 122, 97, 78 or 62 days at constant temperatures of 14, 17, 20, or 23°C, and 93 or 76 days at day/night temperatures of 20/14 or 23/17°C. Flower diameter increased from 7.4 to 8.6 cm as forcing temperature decreased from 23 to 14°C, but temperature had no effect on flower number and inflorescence height. We conclude that pseudobulbs of Miltoniopsis Augres ‘Trinity’ must be sufficiently mature (diameter ≥3.1 cm) before cooling for rapid flowering and a high flowering percentage. Once plants are induced to flower, subsequent development is a function of the average daily temperature.
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