Temperature and development inIrisXhollandicaduring pre-planting storage. II. Floral initiation

Abstract

Floral initiation was studied in Dutch iris bulbs during storage at different temperatures in the dark. Between 2 and 20°C, 90% of bulbs initiated flowers within 54 days but only 10% did so after 105 days at 25°C. Cardinal temperatures for floral initiation were derived from regressions of rates of floral initiation (1/t) on temperature. The basal temperature was found to be ca. -3°C, the optimum was ca. 13°C and the maximum was ca. 27°C. Under constant temperatures, the uniformity of floral initiation was greatest at 9 and 13°C. Transfer of bulbs from 5 to 13°C resulted in floral initiation at a rate similar to that of bulbs held continuously at 13°C, whereas it was delayed in the other transfer treatments. Uniformity of initiation was markedly increased by 14 days at 5°C prior to 13°C. Thermal times of between 291 and 354°Cd were required for floral initiation in 90% of the bulbs, between 186 and 218°Cd for the first 50% to initiate, and 82°Cd for the first 10%. While regression analysis showed these requirements not to differ significantly between bulbs in constant-temperature and in transfer-temperature treatments, only 64% of the variance was accounted for.