APPROACHES TO NONCONVENTIONAL CONTROL OF PLANT-VIRUS DISEASES

Plant viruses cause significant losses to crops worldwide and the three basic approaches to controlling them have not been overly successful. The new concept of nonconventional resistance, which involves transforming plants with nucleic acid sequences that interfere with the viral infection cycle, is a promising new approach. The current nonconventional strategies, those of coat protein-mediated protection. antisense nucleic acids, satellite sequences, defective interfering molecules, and nonstructural genes, are reviewed with their advantages and disadvantages being discussed. The question of what exactly is nonconventional resistance is raised and suggestions are made for defining resistance. A range of strategies that are likely to be developed in the future are outlined together with some guiding principles for selection and deployment of these forms of resistance.