Effect of reciprocal transfers of onion sets between inductive and non-inductive temperatures on the incidence of bolting and bulbing and seed yield

The experiment was conducted at the experimental grounds of the School of Plant Sciences, University of Reading during 1996. Onion sets (22.5 mm diameter) of two cultivars (Hygro and Delta) were transferred from a low (10 °C) to a high (30 °C) temperature and vice versa on six occasions at 15 days intervals. Two control treatments where sets remained at 10 and 30 °C throughout were also included in the experiment for comparison. In both cultivars (Hygro and Delta), plants did not flower when sets were maintained at 30 °C throughout or when given 15 days at 10 °C followed by 30 °C for 75 days. Highest percentage of bolting was observed when sets were maintained for the longest period at 10 °C followed by the shortest period at 30 °C or when given 10 °C throughout. Highest number of florets and seed yield per umbel was recorded in treatments where sets were maintained at 10 °C for 90 days. Mean bulb weight increased where sets remained for longer period at higher temperature (30 °C) either before or after transfer. Bulb yield m−2 increased when sets were initially stored at 10 °C for a short period followed by 30 °C throughout.