Abstract
The effects of TDZ and paclobutrazol on the primary regeneration on tulip flower stalk explants of six cultivars and subsequent shoot multiplication were examined. Explants, flower stalk slices, were excised from cooled and subsequently forced bulbs. The explants were incubated for two months in darkness on medium containing NAA and cytokinins, 2iP and BAP, as control, or TDZ (0.5-4 mg l<sup>-1</sup>) and paclobutrazol (0.05-0.4 mg l<sup>-1</sup>). Then, the regenerating explants were subcultured on medium with TDZ and NAA applied at low concentrations. Different regeneration capabilities were found depending on cultivar and growth regulators. The percentage of explants forming leaf-like structures ranged, on the control medium, from 80% in 'Blue Parrot' and 'Prominence' to below 30% in 'Apeldoorn' and 'Mirjoran'. TDZ, applied at optimum for each cultivar concentration, greatly increased the regeneration potential up to 70-100%. Paclobutrazol, added to the TDZ-containing medium, significantly enhanced the response of explants, resulting in high numbers of leaf-like structures formed per explant (13.7-22.8). The structures developed gradually into characteristic forms: the growing up cotyledonary leaf, the probable root primordium formed at its base, the growing downwards stolon and the shoot meristem developed finely on its tip. It is suggested that such primary regeneration may have a nature of somatic embryogenesis. Then, the adventitious shoots developed and formed clusters, which were divided into 2-3 smaller ones every two months. The growth regulators, used at initial stage, markedly influenced subsequent shoot multiplication. Thus, the most intensive shoot formation was noted with TDZ at concentrations of 0.5-2 mg l<sup>-1</sup> and paclobutrazol of 0.05-0.1 mg l<sup>-1</sup>.
Highlights
The natural rate of a tulip vegetative propagation is insufficient for modern breeding
Development of Abbreviations: BAP 6-benzylaminopurine, kinetin 6-furfurylaminopurine, 2iP 6-(C,C-dimethylallylamino)purine, NAA =-naphthaleneacetic acid, TDZ N-phenyl-N-1,2,3-thiadiazol-5-ylurea, paclobutrazol (2-RS, 3-RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-pentan-3-ol, flurprimidol =-(1-methylethyl-[=-4-(trifluromethyloxy) phenyl]-5-pyrimidinemethanol shoots and bulbs from axillary buds isolated from tulip bulbs was studied by Riviere and Muller (1976)
A relatively high regeneration potential was found in the nodal segments of flower stalks incubated in light (16 photoperiod) in the presence of NAA and BAP, both at the concentration of 1 mg l-1
Summary
The natural rate of a tulip vegetative propagation is insufficient for modern breeding. It takes about 25 years from the crossing to the commercial release of a new tulip cultivar. A relatively high regeneration potential was found in the nodal segments of flower stalks (isolated from bulbs stored at 17°C) incubated in light (16 photoperiod) in the presence of NAA and BAP, both at the concentration of 1 mg l-1. Significant progress in formation of the characteristic for tulip leaf-like structures on flower stalk nodal segments was achieved by Le Nard et al (1987) who obtained a high percentage of regenerating explants (60-90%), due to their in-
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