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

Abstract Bulbs of tulip ( Tulipa gesneriana L. ‘Gander’), in which the formation of floral organs had been completed, were chilled at 2°C for 3–30 weeks and then forced hydroponically at 20°C under a 12 h photoperiod with the light at 100 μmol m −2  s −1 . The fresh weight and the perianth length of the cut flower highly correlated with the dry weights of shoots and floral organs at anthesis, respectively. The dry weights at planting ( DW p ) of shoots, floral organs and daughter bulbs increased with increasing the duration of bulb chilling at 2°C ( t c ). After a 30-week t c , enlargement of daughter bulbs had already started and their DW p was high. The days from planting to anthesis ( t pa ) decreased hyperbolically with increasing t c . The dry weight at anthesis ( DW a ) of shoots increased with increasing t c up to 12 weeks and then decreased. DW a of floral organs decreased and that of daughter bulbs increased with increasing t c . After a 30-week t c , the DW a values of shoots and floral organs were markedly small and that of daughter bulbs was very large. The dry weights of shoots, floral organs and daughter bulbs increased exponentially after planting, and the relative growth rate during the period from planting to anthesis ( R pa ) in each plant part was calculated. The changes of DW a of each plant part after various t c could be explained by their changes in the growth parameters, i.e., DW p , t pa , and R pa which were shown as functions of t c .