Control of plant virus disease

Once infected, it is almost impossible to eliminate a virus infection from a plant by use of antiviral agents. Until recently a reliance on horticultural practice (the use of virus-free seeds, eradication of vectors, choice of planting time, etc.)  Helped to reduce the extent of virus infection but more recently genetic engineering has allowed the construction of plants that show natural resistance to virus infections. Plants do not mount immune responses but there is evidence that prior infection with a nonpathogenic virus can protect plants from infection by a more pathogenic strain. This phenomenon, referred to as pathogen-derived resistance, has been induced deliberately by engineering the tobacco plant genome to contain the coat protein gene of TMV. The resulting transgenic plant was protected from challenge by the wild type but as yet the mechanism of this resistance is not clearly understood.