Factors Affecting the Growth of Daughter Bulbs in the Tulip

The relative growth rate (Rw) of daughter bulbs of the tulip cultivar Rose Copland was remarkably constant during the spring period of growth in four seasons at two sites. The Q10 of Rw was 2.2, and the long period of constant Rw is attributed to compensation of a fall with age by increasing temperatures in the spring. Final bulb weight differed among four cultivars because of differences in Rw and in initial daughter bulb weights. Partial defoliation reduced Rw roughly in proportion to the leaf area removed, and removal of mother bulb scales resulted in reduced leaf area, fewer daughter bulbs, and a lower daughter bulb Rw. Heat-treatment of mother bulbs before planting (blindstoken) killed the flower within the bulb, inactivated the apical dominance exerted by the flower, and resulted in a higher initial daughter-bulb weight at the start of the spring period of exponential growth. The Rw of heat-treated and control daughter bulbs were not different, neither were the leaf areas, so it is assumed that final daughter-bulb weights were higher following treatment because of increased sink strength. The economic implications of these findings are discussed.