Effects of cytokinin treatment of nodal cuts and petioles on shoot regeneration of Campanula portenschlagiana 'Blue Ocean'

Several species of Campanula genus have been cultivated as ornamental plants and there is still a growing demand for more attractive characters that could be achieved through breeding, including genetic manipulation. While competence and condition of transformed tissue have a direct effect on the success of gene transformation, obtaining an efficient protocol with balanced hormonal content, which induce healthy shoot regeneration, is necessary. To determine the optimum type and concentration of cytokinins, that induce shoot regeneration in Campanula portenschlagiana 'Blue Ocean', an experiment in two phases (I and II) was designed. In the initial phase (I), nodal cuts were harvested from mature greenhouse-grown plants and cultured on Murashige and Skoog (MS) media containing various concentrations of benzyladenine (BA) or thidiazuron (TDZ). In the second phase (II), petioles were harvested from the newly grown shoots, derived from the nodal cuts and were cultivated on MS media supplemented with different concentrations of BA or TDZ for shoot regeneration. Results revealed that the best rate of axillary node growth were exhibited by the nodal cuts, which were cultivated in medium containing 0.5 mg L^-1 TDZ (in phase I). The most favorable shoot regeneration rate was obtained from petioles cultivated in 1.0 mg L^-1 TDZ (in phase II). According to the results of this experiment, effect of hormone treatment in phase I on improving the shoot regeneration efficiency in phase II was not significant. Consequently, the final hormonal content of the media elicited a direct influence on the rate of shoot regeneration.