PLANT IMPROVEMENT - GENERATING VARIATION AND SELECTING BETTER PLANTS
The deliberate hybridisation of both cultivars or of closely related species to combine the desirable characteristics of both parents followed by selection is currently the most common method of plant improvement. Improved cultivars can sometimes be selected from relatively small hybrid populations but success is more likely when selection is from large populations, e.g. about 50000 seedling vines have been studied in the CSIRO Grape Vine Breeding Program since 1965.
Other methods to generate variation include gamma irradiation, application of chemical mutagens and the search for naturally occurring bud mutations. Somaclonal variation which occurs when plants are regenerated from groups of cells, single cells or protoplasts is a useful additional technique to generate variability in some species. In the case of woody fruiting species plant performance can be greatly modified by rootstocks. In this way it is possible to alter plant vigour, crop yield, and fruit quality of well established cultivars. In many cases horticulturists do not wish to alter fruit quality of established cultivars but wish to change growth characteristics. Current research using genetic engineering techniques aims to insert specific genes such as those responsible for disease, insect and herbicide resistance into well established cultivars.