The bulbing response to day length and temperature of some Australasian cultivars of onion (Allium cepa L.)

Abstract

Onions (Allium cepa L.) were grown in the Canberra phytotron from seed to bulb in three day lengths (11, 14 and 17 h) and five temperature regimes (day/night 18/10¦, 22/14¦, 26/18¦, 30/22¦, 34/26¦), The cultivars Creamgold, Braeside Golden Globe, Gladalan Brown and Early Lockyer Brown were used. There was a significant interaction of cultivar, day length and temperature on bulbing. Bulbing was most rapid at the highest temperature and longest day length. Creamgold exhibited a temperature dependence in bulbing, so that at 18/10¦C bulbing did not occur at any day length. The other cultivars bulbed at low temperatures. Lateral buds developed in Braeside Golden Globe, but not at low temperatures (18/10¦) or in long day lengths (14 or 17 h) where normal bulbs were produced. In an attempt to simulate field conditions more closely, some plants were transferred to different day length and temperature treatments between sowing and harvest. During development, neither bulbing ratio (leaf base diameter/neck diameter) nor final bulb size was significantly different from those of plants grown from seed to maturity in one regime. Bulbing required the continual presence of bulb-inducing conditions: bulb development ceased on transfer to unfavourable conditions (short day lengths, low temperature).