Effect of forcing solution used to break the seasonal influence on in vitro axillary bud sprouting of two Leucospermum (R.Br.) cultivars.

Abstract

In woody plants, the availability of plant material for in vitro use is usually limited to the short active growth period of the mother plants. To overcome this limitation, an effective protocol is described to break the seasonal effect on in vitro axillary bud sprouting in Leucospermum cordifolium ‘Flame Spike’ and Leucospermum ‘Tango’. This enables homogenous production throughout the year. Shoots were harvested at four different times of the year, sterilized and cultured in forcing solutions containing a quarter-strength of Murashige and Skoog medium salts (MS, 1962), supplemented with benzyladenine (BA) (0-100 mg L-1) and gibberellic acid (GA3) (0 or 10 mg L-1). Ascorbic acid at 150 mg/l was added to avoid explant oxidation. After 10 days, multinodal explants were cultured on half-strength MS solid growth regulator-free medium or with GA3. Three weeks later, explants were subcultured in fresh medium. The effect of pre-treatment is very clear in the case of L. cordifolium ‘Flame Spike,’ where the percentages without pre-treatment reached 20% in the August 2014 harvest and the maximum was 53.81% in November 2013 in those with pre-treatment. Although the effect of forcing solutions in L. ‘Tango’ was not evident, supplementation with 50 mg L-1 BA turned out to be optimal in February, May and August 2014. Its use also reduced the time required for in vitro establishment of explants in both cultivars.