Effect of cold temperature durations of onion sets in store on the incidence of bolting, bulbing and seed yield

The experiment was conducted at the experimental area of the School of Plant Sciences, University of Reading during 1996. The planting material comprised of sets (graded to 22.5 mm diameter) of two cultivars, Hygro and Delta. The sets were stored at 5 °C for nine chilling durations, between 10 and 90 days. A control treatment (sets stored at room temperature of 20 °C for days) was also included in the experiment for comparison. Sets of both cultivars treated for 90 days at 5 °C, produced nearly seven times more bolters than those treated for 20 days. Cool temperature treatment for 10 days was too short to induce bolting. Number of florets and percentage of seed bearing florets per umbel increased with lengthening cold durations and this resulted in higher seed yield per umbel. Mean bulb weight per plant was found to increase with shortening the period of low temperature treatment. For bulb crop, storage of sets at 20 °C for 90 days appears to be optimum, as it checked bolting and increased average bulb weight and bulb yields m−2 in both cultivars.