RESEARCH ON THE GROWTH, DEVELOPMENT AND MICROPROPAGATION OF TWO PLECTRANTHUS CULTIVARS IN GUANGZHOU, CHINA

Plectranthus × hilliardiae 'Edelblau' and P. madagascariensis ‘Marginatus’ (Lamiaceae) are decorative plants grown in South Africa. Growth requirements and vegetative and floral development of these cultivars were studied under climatic conditions in Guangzhou, South China and methods for cutting and micropropagation were established. The optimum temperature for ‘Edelblau’ growth was between 20–26°C and optimum humidity was between 80–90%, at which the rate of growth reached 0.45 cm.day^-1. The adventitious rooting percentage for ‘Marginatus’ cuttings treated with 12.5 mg.L^-1 IBA in water culture was 94.1%, as opposed to only 80% and 6% in sand or in soil culture, respectively. The optimum medium for inducing bud sprouting in ‘Edelblau’ in vitro, when stem segments were used as explants, was 1/2 MS + 20 mg.L^-1 lactalbumin hydrolysate (LH), 20 mg.L^-1 casein acid hydrolysate (CAH), 20 mg.L^-1 yeast extract (YE) and 0.25 mg.L^-1 N-phenyl-N-(4-pyridyl)-urea. The bud regeneration percentage of growth in the MS medium containing 0.25 mg.L^-1 N-phenyl-N-(4-pyridyl)-urea (4-PU) and three nutrition components was 420% relative to controls. 0.1 mg.L^-1 6-BA (6-benzyladenine) caused bud regeneration to increase 4.4 times in vitro in stem segments of ‘Marginatus.’ The best medium for inducing adventitious root formation in ‘Edelblau’ and ‘Marginatus’ was MS supplemented with 0.25 mg.L^-1 IBA (indolebutyric acid) or 0.5 mg.L^-1 NAA (naphtbalene acetic acid), respectively. These positive results position both cultivars for introduction into the Guangzhou nursery industry.