Inflorescence development in an Ornithogalum dubium hybrid as influenced by bulb temperature treatments

Abstract

SummaryOrnithogalum dubium hybrid 327 clone 2 (‘327-2’) bulbs were stored dry at 10°, 16°, 22°, 28°, and 35°C for six weeks after harvest. After storage, bulbs were evaluated by nuclear magnetic resonance imaging (MRI) to obtain the spin-lattice relaxation time (T1) profile across the transverse section of intact bulbs, by scanning electron microscopy (SEM) to observe inflorescence development, and by forcing in a 18.5°/18°C greenhouse to observe growth and flowering responses. Bulbs treated at 10°C had the shortest T1 (0.33 ms) through the bulb which is largely composed of scales. Leaf emergence from bulbs treated at 10°C was delayed, and plants failed to flower. This indicated that bulbs were dormant and dormancy was not broken, thus delaying initiation of floral organs. Bulbs treated at 22°C and 28°C formed the primary inflorescence with several florets. At the base of the primary scape of bulbs treated at 22°C, a vegetative apex was observed by both MRI and SEM. In the centre of bulbs where both leaves and floral organs were present, T1 was longer than that of the scales. This suggests that dormancy in the scales was broken and the leaves and scape were ready to emerge. Flowering was fastest when bulbs were treated at 22°C. The number of florets was the highest (16.0 florets) and fewest (12.6 florets) when bulbs were treated at 22°C and 35°C, respectively. Ornithogalum dubium bulbs stored at 25° and 30°C for six weeks flowered from 14 and 17 bulbs, respectively, out of 22 and flowered earlier than when stored either at lower or high temperatures. The response obtained O. dubium ‘327-2’ hybrid was attributed to its pedigree involving O. dubium. Due to its non-destructive nature, MRI can be used to observe inflorescence development inside the bulbs during bulb storage and possibly to study the state of dormancy.