Effect of different cytokinins on axillary shoot proliferation and elongation of several genotypes of Sequoia sempervirens

Five genotypes of Sequoia sempervirens were cultured in vitro. Stem segments of greenhouse-grown plants were disinfested and grown on a Wolter and Skoog (WS) medium without growth regulators for 4 wk. Newly developing shoots from axillary buds were then subcultured onto fresh media containing several different cytokinins at a concentration of 5 μM each per treatment. The following cytokinin treatments were used: benzyladenine (BA), BA plus adenine hemisulfate, N-benzyl-9(2-tetrahydropyranyl) adenine (BPA), N6-[2-Isopentenyl]adenine (2ip), kinetin, thidiazuron (TDZ), and zeatin. Each genotype responded differently to tested cytokinins. The use of zeatin resulted in the highest number of shoots and the longest shoots for three genotypes of S. sempervirens. In another experiment, shoots from three genotypes were grown on the same basal medium described above and supplemented with zeatin at six different concentrations (2.5, 5, 10, 15, 20, and 30 μM). For all zeatin concentrations, significant differences among genotypes for shoot proliferation were observed. When all five genotypes were grown under three concentrations of zeatin (5, 10, and 15 μM), differences among genotypes were observed for both shoot proliferation and shoot length. The influence of the culture medium on the overall micropropagation protocol of S. sempervirens is discussed.