Some aspects of the tissue culture and micropropagation of Boronia megastigma Nees

This study investigates the effects of a number of factors on the growth and development of Boronia megastigma Nees in \in vitro\" culture. A number of non-nutrient factors were found to be influencing the growth and development of cultures. The pH of the medium was found to have an effect on the subsequent growth of the cultures as did the orientation of explants on the medium and the mode of trimming the explants. Relative Growth was found to be an inappropriate measure of the growth of the cultures. Nitrogen nutrition was by far the most important factor affecting growth in the nutrient media. The concentration of nitrogen was found to be influencing the amount of growth and the balance between shoot initiation and shoot extension. The cultures grew poorly in the presence of either ammonium or nitrate as a sole source of nitrogen. Changes in the pH of the medium were found to be the cause of the poor growth on media containing ammonium as the sole nitrogen source. Changes in the pH of the medium were also associated with the use of nitrate as the nitrogen source however correction of the pH change using succinate buffer did not improve growth on this medium. Adenine hemi-sulphate and vitamins had little influence on the growth and development of the cultures. Sucrose concentration was found to influence growth possibly by affecting the osmotic potential of the medium. The rate of root initiation in culture was also substantially affected by the level of nitrogen in the medium. Development of cultures after root initiation was found to be substantially affected by both the level of nitrogen in the root initiation medium and the level of nitrogen in the proliferation medium prior to root initiation. Root initiation was also affected by the concentration of sucrose in the medium while adenine hemi-sulphate had no effect. Survival of plantlets after planting in soil was substantially affected by the length of the time spent on root medium. The effect on plantlet survival of temperature conditions during the root initiation phase was also Investigated. The results obtained from this research should assist In the commercial micropropagation of Boronia megastigma and provide a basis for future research on the in vitro culture of this species."