Basal medium improvement for routine micropropagation of Olea maderensis: physiological comparative studies

Abstract

The routine micropropagation of Olea maderensis (Lowe) Rivas Mart. & Del Arco requires an adequate basal medium. To find the optimal basal medium, shoots were grown on four different media: olive medium (OM) and three modified OM media enriched with 2, 4, and 10 times the iron (Fe), magnesium (Mg), and manganese (Mn) concentrations of the OM medium, respectively (OMG, OMG4, and OMG10). For the elongation–proliferation stage, media were supplemented with 9.12 µmol·L–1 zeatin. Doubling the Fe, Mg, and Mn concentrations (OMG) provided green and healthy shoots, while in other media leaf chlorosis or necrosis and abscission occurred because of either deficiency (OM) or toxicity of the elements (OMG4 and OMG10). Shoots grown in the OMG medium also had the highest elongation–proliferation rates. Physiological studies were then performed only between OMG- and OM-grown shoots. Chlorophyll a and b contents and fluorescence (Fv, Fm) were higher in OMG-grown shoots. Doubling the concentration of Fe, Mg, and Mn (which are important in photosynthesis) stimulated leaf survival and photosynthesis. OMG-grown leaves had higher Mg, Fe, and Mn levels. Compared with field leaves, in vitro leaves had higher protein contents. Other physiological parameters (membrane integrity, water content, and osmolality) did not differ between the two media. The best rooting rates were obtained for shoots grown in OMG (>85%), and plants were successfully acclimatized. These studies improved the efficiency and quality of micropropagation of O. maderensis, thereby allowing germplasm preservation of this endangered species.