Analysis of the effects of bulb chilling duration and forcing temperatureson growth of tulips forced hydroponically

Bulbs of Tulipa gesneriana L. 'Gander', chilled at 2 degrees C for 12, 18 o r 30 weeks were grown hydroponically at 12, 16 or 20 degrees C under a 12-h r photoperiod to force them into growth. With increasing the forcing temper ature, the dry matter accumulated in new organs, i.e. shoots and daughter b ulbs at anthesis decreased and dry matter remained in mother bulbs increase d. In bulbs chilled at 2 degrees C for 30 weeks, more dry matter stored in the mother bulbs was partitioned to the daughter bulbs rather than to the s hoots at anthesis, compared to bulbs chilled for 12 or 18 weeks. Irrespective of chilling durations (t(c)), apparent activation energy (E-a) of reciprocal of days from planting to anthesis (1/t(pa)), which was calcu lated by Arrhenius' law, was larger than E-a of relative growth rate (R-pa) of shoots and daughter bulbs. This finding indicates that the change in t( pa) has greater impact on the final accumulation of dry matter in new organ s than that in R-pa of individual organs. The relative values (I-r; 1 at 20 degrees C of forcing temperature) of t(pa ) and R-pa of shoots and daughter bulbs were calculated for each chilling d uration. The change in I-r of t(pa) and R-pa with forcing temperature was e xponential. The results of multiple regression analysis showed that bulb ch illing duration has little impact on I-r.