Propagation of eight cultiv ars of Rhododendron in vitro using agar-solidified and liquid media and direct rooting of shoots in vivo

Sterile cultures were obtained from expanding buds of Rhododendron cultivars ‘Pink Pearl’, ‘Nova Zembla’, ‘Gomer Waterer’, ‘Hugo Koster’, ‘Britannia’, ‘America’, ‘Wilgens Ruby’ and ‘Doncaster’. Shoot-producing cultures were obtained from all cultivars except ‘Doncaster’. Yield of shoots on agar-solidified medium varied with each cultivar. For ‘Pink Pearl’, shoot production with liquid medium was 10-fold higher than with agarsolidified medium. Shoots were readily rooted in vitro and in vivo. Rooting percentages of 50–70% were obtained after 5 weeks when unrooted shoots were transferred to a peat substrate. This was increased consistently to 80–90% by pre-treating shoots in a solution of minerals, vitamins and sucrose. Pre-treatments for at least 10 days in medium supplemented with indolebutyric acid (5–15 mg l−1) significantly (P ≤ 0.05) increased the number of roots produced per shoot. A pre-treatment period of at least 10 days was required for optimal rooting.