Relationships between Bulb Size, Apex Size and Flowering in Bulbous Iris cv. Ideal

Large, retarded bulbs of the Iris cv. Ideal flower readily after exposure to appropriate preplanting conditions, whereas smaller bulbs flower with decreased frequency. Flower initiation occurs when apices from large, retarded bulbs are cultured on either Murashige-Skoog medium supplemented with gibberellic acid, or on the same medium without gibberellic acid on which scales from large bulbs have been incubated. Since floral initiation seldom occurs in explants from small bulbs, it is likely that reduced flowering of small bulbs relates in part to characteristics of the apical meristem. Apical dome diameter is one characteristic of retarded (and freshly dug) bulbs that is positively correlated with bulb size. However, whereas prolonged storage at retarding temperature increases the frequency of flowering of smaller bulbs, there is not a concomitant increase in apical dome diameter. Moreover, the ratio of apical dome diameter to bulb size in freshly dug bulbs does not increase measurably with later digging date indicating that apical dome size is not correlated with bulb maturity.