Effect of set-size and storage temperature on bolting, bulbing and seed yield in two onion cultivars

The effects of three set-sizes (12.5. 17.5 and 22.5 mm in diameter) and seven storage temperatures (0, 5, 10, 15, 20, 25 and 30 degrees C) on bolting, bulbing and seed yield in two onion (Allium cepa L.) cultivars 'Hygro' and 'Delta' were investigated. The incidence of bolting increased linearly with set-size and curvi-linearly with decreasing storage temperature. Time to inflorescence emergence and floret opening showed a curvi-linear response to storage temperature with the earliest inflorescence emergence and floret opening occurring at 5 degrees C and the latest at 30 degrees C for 'Hygro' and at 25 degrees C for 'Delta'. Seed yield per umbel also showed a curvi-linear response to storage temperature with the lowest seed yield occurring at 30 degrees C for 'Hygro' and at 25 degrees C for 'Delta' and the highest seed yield at 5 degrees C. For a seed crop, storage of large sets (22.5 mm) of these cultivars at 5 degrees C for 120 days appeared to be optimum with 5-12% higher seed yield per umbel than that of 90 days storage. Bulb yield showed a curvi-linear response to storage temperature with the highest bulb yield occurring at 25 degrees C and the lowest at 5 degrees C. (C) Published by Elsevier B.V.