Morphological Studies of Flower Bud Initiation and Development in Bulbous Iris Stored at Various Temperatures1,3

Flower buds are absent in dormant iris bulbs, but floral initiation occurs after subjecting them to a high temp, heat curing treatment, followed by a holding period at a moderate temp, and then a low temp pre-cooling period. The effects of cultivars, digging dates, ethylene gas treatment, and different storage temp on earliness and uniformity of flowering were studied in microscopic sections of bulb growing points of samples collected at intervals from the different treatment lots. The results indicated that variations in field growing conditions produced bulbs with varying degrees of maturity, of which some would respond properly to curing treatments and others would not. Properly matured bulbs grown in the Pacific Northwest can be heat cured by exposing them to a temp of 32.2°C for 10 days. Holding temp lower than 15.5°C delayed subsequent flower bud initiation. Ethylene gas treatment prior to heat curing appeared to stimulate floral initiation.