Effects of Photoperiod, Nitrogen Nutrition and Temperature on Inflorescence Initiation and Development in Onion (Allium cepa L.)

Abstract

The effects of photoperiod, nitrogen nutrition and temperature on inflorescence initiation and development in onion cv. Rijnsburger and cv. Senshyu Semi-globe Yellow were studied in controlled environments. Rates of inflorescence initiation were estimated using the data for leaf numbers formed prior to flower formation and the rates of leaf initiation. At 9 °C inflorescence initiation was accelerated by long photoperiods particularly for cv. Rijnsburger where the average time for initiation was 86 days in 8 h and 38 days in 20 h photoperiods. Initiation was as rapid at 12 °C as at 9 °C but was slower at 6 °C. A reduction in the nitrate concentration in the nutrient solution from 0.012 to 0.0018 M greatly accelerated inflorescence initiation particularly in photoperiods and temperatures not conducive to rapid initiation. Cv. Senshyu initiated more slowly than cv. Rijnsburger and was less sensitive to photoperiod and nitrogen level. The development rate of inflorescences after initiation was accelerated by long photoperiods and increases in temperature from 6 to 12 °C but was retarded by the lower nitrogen level.