Articles
CONTROL OF BOLTING AND FLOWERING IN CARROT
The object of the experiments described here was to examine juvenility and plant growth rate as factors that might be manipulated to make carrots less sensitive to flower induction by chilling.
The cultivars Chantenay Red Cored and Amsterdam Forcing were shown to differ in the chronological age at which the juvenile phase ended.
Chantenay became ripe-to-flower after about 6 weeks growth from seed whereas Amsterdam Forcing required about 8 weeks.
In terms of physiological age measured as number of leaves initiated by the start of chilling, however, both cultivars became ripe-to-flower at the 7.5 leaves stage.
In controlled environment experiments, the responsiveness of the plants to chilling increased with age as long as there was no restriction to growth through pot size.
Different growth rates were established in similar aged carrots prior to chilling by transferring plants from 9 cm to 13 cm diameter pots at various times.
Plants with the faster rate of leaf development at the onset of chilling were the most sensitive.
Whether the rate of leaf development per se is the determinant of sensitivity to vernalisation or merely correlated with it is not yet known.