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 tw o evergreen azalea genotypes was investigated. A 5 x 5 factorial exper iment was conducted with varying TDZ and IAA levels to determine optim um shoot organogenesis from leaf tissues of 'Fuchsia' and 'Hino Crimso n'. Leaf explants grown on a medium containing 22.7 mu M TDZ and 22.8 mu M IAA produced the highest shoot regeneration frequency for both 'F uchsia' (64%) and 'Hino Crimson' (82%), and developed the highest mean number of shoots per explant, 5.9 and 4.9; respectively; Incubation o f leaf explants in the dark for one week followed by culture under low -light intensity (30 mu mol m(-2)s(-1) for five weeks, or incubation i n the dark for two weeks followed by culture under either low-light or high-light intensities (90 mu mol m(-2)s(-1)) for four weeks resulted in the highest shoot regeneration frequencies and mean number of shoo ts per explant. Shoot regenerants were subcultured onto Anderson's med ium with 0, 1.2 and 2.3 mu M TDZ, or 2.3 mu M zeatin to promote elonga tion. Although a higher rate of shoot proliferation was observed on me dia containing TDZ, a cytokinin-free medium or a medium containing 2.3 mu M zeatin induced higher numbers of long (>1 cm) shoots.