Effects of duration of bulb chilling on dry matter distribution in hydroponically forced tulips

Bulbs of tulip (Tulipa gesneriana L. `Gander'), in which the formation of ̄oral organs had been completed, were chilled at 28C for 3±30 weeks and then forced hydroponically at 208C under a 12 h photoperiod with the light at 100 mmol mÿ2 sÿ1. The fresh weight and the perianth length of the cut ̄ower highly correlated with the dry weights of shoots and ̄oral organs at anthesis, respectively. The dry weights at planting (DWp) of shoots, ̄oral organs and daughter bulbs increased with increasing the duration of bulb chilling at 28C (tc). After a 30-week tc, enlargement of daughter bulbs had already started and their DWp was high. The days from planting to anthesis (tpa) decreased hyperbolically with increasing tc. The dry weight at anthesis (DWa) of shoots increased with increasing tc up to 12 weeks and then decreased. DWa of ̄oral organs decreased and that of daughter bulbs increased with increasing tc. After a 30-week tc, the DWa values of shoots and ̄oral organs were markedly small and that of daughter bulbs was very large. The dry weights of shoots, ̄oral organs and daughter bulbs increased exponentially after planting, and the relative growth rate during the period from planting to anthesis (Rpa) in each plant part was calculated. The changes of DWa of each plant part after various tc could be explained by their changes in the growth parameters, i.e., DWp, tpa, and Rpa which were shown as functions of tc. # 2000 Elsevier Science B.V. All rights reserved.