Formation of tulip bulbs in vitro

The propagation of tulip (Tulipa gesneriana L.) in vitro fully depends on vegetative bulb formation. To determine the internal and external factors influencing bulb development, the in vitro shoots of two cultivars of tulip were used for experiments: 'Blue Parrot'-with high rate of shoot multiplication but difficult-to-form bulbs, and 'Prominence'-well multiplying and easily forming bulbs. Effects of exogenous abscisic acid (ABA), methyl jasmonate (MeJA) and gibberellin (GA(3)) as well as environmental factors (light, darkness and cooling period) and the kind of gelling agent on bulb formation were studied. Contents of endogenous plant hormones for in vitro shoots were determined by ELISA. The content of ABA and trans-zeatin riboside (t-ZR) in 'Blue Parrot' was significantly higher than in the shoots of 'Prominence'. After cooling (4degreesC), the content of endogenous ABA in shoots of 'Blue Parrot' decreased, but it was still 70% higher than in the 'Prominence' shoots before the low temperature treatment. The level of endogenous cytokinins (t-ZR and IPA-isopentenyladenosine) in 'Blue Parrot' significantly increased after cooling. Bulb formation of this cultivar was negatively influenced by ABA application. The results suggest that the poor capacity for bulbing observed in 'Blue Parrot' may result from high concentration of endogenous ABA and t-ZR in the shoots of this cultivar. A significant improvement of bulb development was obtained by extending the cooling period up to 14 weeks, as well as by application of MeJA and activated charcoal into the medium.