Genetic modification of plants: significant issues and hurdles to success.

Transformation and regeneration is routine for many crop plants. A genetically engineered tomato with a longer shelf life at full ripeness was introduced in the United States in 1994, and other soon-to-be-released products, both foods and fibers, incorporate genes for resistance to pests, diseases, and environmentally benign herbicides. Other possibilities are altered plant fats and oils, methionine- and lysine-enhanced grain and legume proteins, plant foods that can deliver immunizing antigens, and other ways of controlling fruit ripening. Food safety concerns include the inadvertent production of toxicants and allergens. Foreign DNA can be introduced into plants by bacterial vectors, direct uptake by protoplasts, and mechanical introduction on metal particles or other materials. Limitations include little or no control of copy number or site of integration of the introduced DNA, dependence on selectable markers for recovery of traits, and inadequate knowledge of how to control key metabolic steps to maximize desirable traits. Directed genetic change still requires conventional crop breeding to deliver benefits to farmers and consumers.