Tissue Culture as a Method for Vegetative Propagation of Forest Trees

A review of the world's literature indicates that almost all parts of a plant can be induced to form callus if given the proper stimulus. For some plants the callus can be redifferentiated to form shoots and roots. For others, it is possible to initiate embryoids. There appears to be no reason why forest trees can not be propagated by means of tissue culture. INTRODUCTION Research in propagation and breeding has made tree breeders more aware of their inability to propagate many common tree species vegetatively. At the same time, failure to produce a number of desirable interspecific and intergeneric crosses due to inadequate development of ovules or ovaries has raised interest in the technique of tissue culture. Potentially this technique can enable the plant breeder to produce and multiply valuable clonal stocks and hybrids for testing and for production planting. Methods of clonal propagation in forestry, like those of agriculture and horticulture, are very traditional. Practices such as grafting, cutting, air-layering and bench propagation have not changed in centuries. However, these techniques cannot be successfully applied to all plants, and additionally several of the practices need clearer scientific understanding if they are to be successful. For example, the physiological causes responsible for differences in rooting responses of shoots taken from various regions of trees are not known. There are other factors like the time of sampling of the explants, age of the donor plant and seasonal variation in the rooting ability of woody cuttings which also make these techniques quite problematic. Further, there are many tree species and varieties whose cuttings do not root or root with extreme difficulty. While the age-old conventional methods of plant propagation will continue to hold good for years to come, new techniques like those of tissue culture have also to be adopted if progress is to> be expected. Methods of establishing and maintaining tissue cultures have been well described by several authors, including Gautheret (1959) and White (1963). Fundamentally, the principles of sterile culture technique are followed. There is no one method of growing explants in vitro. The basic approach is simply to place a living sterile tissue on a medium that will induce cell division. The main effort in vegetative propagation of forest trees should aim at growing N.Z. J. For. Sci. 4 (2): 279-90 280 New Zealand Journal of Forestry Science Vol. 4 isolated plant parts to obtain initially a subculturable callus*. Often this callus can be made to shoot or root under appropriate chemical stimulation. It has also proved possible to induce callus to form embryoids.t In certain cases all three reactions can be induced on the same callus. The plants that are obtained by these methods are genetically similar to the parental ones and hence this technique can be an ideal method for vegetative propagation. This communication sets out to highlight the achievements of tissue culture and to show the various ways plant organs or parts can respond to this technique and yield new plants vegetatively. The forestry scientist can utilize the method most suitable to his particular need.