ABSTRACT
Grape (Vitis sp.) is the world’s most valuable fruit crop as a result of its unique use for wine and as a fresh fruit and raisin. For wine, phenotype is particularly important and varietal fidelity is of paramount concern. Development of new varieties is hampered because grape is a woody perennial species with a life cycle of 2 to 5 years. It exhibits inbreeding depression so that homozygous lines cannot be developed and, in a breeding program, vigor must be scrupulously maintained by outcrossing. All of these factors conspire so that grape varieties must be propagated vegetatively to maintain clonal fidelity, and use of breeding is not a particularly viable method for improvement (although it is used successfully to breed new seedless table grapes). In all other instances, varietal improvement is achieved incrementally by selection of variant phenotypes from stands of established varieties. Such “clonal selection” (1) has been effectively used to produce recognizable subclones of many varieties. However, clonal selection is a random, “hit-or-miss” approach that does not allow intentional introduction of desirable traits, such as disease resistance. Like most crops, grape is subject to continual disease pressures; it would be advantageous to utilize genetic improvement to maintain or improve established production standards in existing viticul-tural regions and allow wider environmental adaptation so that grape production can be expanded into previously inhospitable regions. Genetic transformation is an attractive alternative for genetic improvement because it potentially alleviates the shortcomings of conventional approaches by allowing addition of specific traits into otherwise desirable varieties.
