Abstract
July and September. The most efficient regeneration and axillary multiplication were achieved on the medium supplemented with meta-topolin. The application of BAP caused a lower regeneration potency of explants and resulted in a decrease of shoot quality with every subculture. Four of the six cultivars showed growth inhibition after three months of growth on BAP-medium. The highest multiplication rate (2.7-4.7 depending on genotype) and the high quality of shoots were noted on the medium supplemented with mT (0.5-1.0 mg l<sup>-1</sup>). It is also very important to note that mT had stimulating effect on organogenesis in <em>P.</em> × <em>hederaefolium</em> and <em>P.</em> × <em>hortorum</em> cultivars over the long term. Moreover, meta-topolin had no after-effect on the growth and inhibition of rooting. Only one cultivar ("Sofie Cascade") rooted better on control medium without auxin. In case of the other cultivars, IBA added in concentrations of 0.01-0.1 mg l<sup>-1</sup> had a stimulating effect on root production. The higher level of auxin inhibited root formation, stimulated senescence of shoots and had a negative after-effect on acclimatization in greenhouse conditions.
Highlights
The basic factor for a profitable mass production of Pelargonium × hortorum and Pelargonium × hederaefolium cultivars is a healthy starting material
On MS medium supplemented with meta-topolin (0.2 mg l-1), as well as BAP (0.1 mg l-1) added together with IBA (0.02 mg l-1), shoot tips and axillary buds of all Pelargonium cultivars developed into a single shoot
In the present study there were no significant differences between cytokinin treatments in growth and development of buds in most Pelargonium cultivars when explants were collected in the spring
Summary
The basic factor for a profitable mass production of Pelargonium × hortorum and Pelargonium × hederaefolium cultivars is a healthy starting material. Micropropagation based on axillary shoot growth is a good system for maintaining an in vitro stock of pathogen-free mother plants (Reuther 1988). Abbreviations BAP 6-benzylaminopurine; IBA 3-indolebutyric acid; mT (meta-topolin) 6-(3-hydroxybenzylamino)purine; MS Murashige and Skoog medium; 2iP isopentyladenine ration ability in the initiated shoots of various cultivars (Reuther 1988; Paludan 1991; Desilets et al 1993; Mithila et al 2001). It is a serious limiting factor in maintaining stock cultures over the long term
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