Bulb dormancy in onion. I. The effects of temperature and cultivar on sprouting and rooting

SummaryThe effects of temperature on dormancy characteristics were investigated in bulbs of various cultivars of onion (Allium cepa). The optimum temperature for sprouting in dry storage ranged from 10 to 25°C. depending on cultivar, for rooting in moist vermiculite from 10 to 15°C. The optimum temperature for root and sprout elongation in non-dormant bulbs was 25°C. A three-week treatment of 35°C after harvest shortened time to rooting and sprouting at 15°C, but a continuous exposure to temperatures above 25°C strongly inhibited both processes. Genetic variation in dormancy characteristics was investigated at 10°C in ten onion cultivars. Time to 50% rooting and subsequent sprouting in moist vermiculite ranged from 8–63 d and 49–156 d, respectively. Time to 50% sprouting in dry storage ranged from 149–310 d. Within the bulb samples a large bulb-to-bulb variation for time to rooting and sprouting was found. Time to sprouting in dry storage did not correlate with the other dormancy characteristics. Implicat...