Micropropagation of Juniperus phoenicea from adult plant explants and analysis of ploidy stability using flow cytometry

Abstract

We report here the successful micropropagation of adult Juniperus phoenicea L. with respective ploidy stability studies. Microcuttings with axillary buds were grown on five media supplemented with different growth regulator combinations. Best elongation rates were achieved on Driver and Kuniyuki (DKW) medium supplemented with kinetin alone or with naphthaleneacetic acid (NAA), while Rugini olive (OM) medium stimulated the development of new branches. Shoots growing on Murashige and Skoog (MS) medium browned and showed necrotic zones. Shoots of second to fourth subcultures usually had higher elongation rates than those of the first culture. For rooting assays, half strength DKW and OM media, different concentrations of growth regulators, auxin continuous exposure vs. dipping and the type of solid matrix were assessed. During rooting assays, two morphotypes were observed with one type having well developed internodes and the other showing hyperhydratation and no internode development. High rooting rates (40 %) were only obtained in the first morphotype shoots exposed for 5 min to 2.4 µM IBA and then transferred to OM medium without growth regulators. Plants were acclimatized in pots containing a mixture of peat and Perlite (3:2) in greenhouse with progressive reduction of relative humidity. A flow cytometric screening for major ploidy changes revealed no differences among the morphotypes and between them and the mother plant. Also the nuclear DNA content of this species was estimated for the first time using flow cytometry (2C = 24.71 pg).