Effect of growth regulators, dark treatment and light intensity on shoot organogenesis from leaf tissues of evergreen azalea

The influence of several factors on in vitro shoot organogenesis of two evergreen azalea genotypes was investigated. A 5 x 5 factorial experiment was conducted with varying TDZ and IAA levels to determine optimum shoot organogenesis from leaf tissues of 'Fuchsia' and 'Hino Crimson'. Leaf explants grown on a medium containing 22.7 μM TDZ and 22.8 μM IAA produced the highest shoot regeneration frequency for both 'Fuchsia' (64%) and 'Hino Crimson' (82%), and developed the highest mean number of shoots per explant, 5.9 and 4.9, respectively. Incubation of leaf explants in the dark for one week followed by culture under low-light intensity (30 μmol m^-2 s^-1) for five weeks, or incubation in the dark for two weeks followed by culture under either low-light or high-light intensities (90 μmol m^-2 s^-1) for four weeks resulted in the highest shoot regeneration frequencies and mean number of shoots per explant. Shoot regenerants were subcultured onto Anderson's medium with 0, 1.2 and 2.3 μM TDZ, or 2.3 μM zeatin to promote elongation. Although a higher rate of shoot proliferation was observed on media containing TDZ, a cytokinin-free medium or a medium containing 2.3 μM zeatin induced higher numbers of long (>1 cm) shoots.