Factors Affecting the Growth of Daughter Bulbs in the Tulip

The relative growth rate (R_w) of daughter bulbs of the tulipcultivar Rose Copland was remarkably constant during the springperiod of growth in four seasons at two sites. The Q₁₀ of R_wwas 2.2, and the long period of constant R_w is attributed tocompensation of a fall with age by increasing temperatures inthe spring. Final bulb weight differed among four cultivarsbecause of differences in R_w and in initial daughter bulb weights. Partial defoliation reduced R_w roughly in proportion to theleaf area removed, and removal of mother bulb scales resultedin reduced leaf area, fewer daughter bulbs, and a lower daughterbulb R_w. Heat-treatment of mother bulbs before planting (blindstoken)killed the flower within the bulb, inactivated the apical dominanceexerted by the flower, and resulted in a higher initial daughter-bulbweight at the start of the spring period of exponential growth.The R_w of heat-treated and control daughter bulbs were not different,neither were the leaf areas, so it is assumed that final daughter-bulbweights were higher following treatment because of increasedsink strength. The economic implications of these findings arediscussed.