ABSTRACT
Compared with fungi and bacteria, plant viruses are the third important pathogens on cultured plants (1,2). They rely completely on host cells for replication and gene expression, and that is why numerous attempts to cure infected plants by chemical treatment have been unsuccessful. Therefore, plant virologists have focused their research on quarantine measures (diagnosis, establishment of virus-free cultures), control of virus vectors (insects, fungi, and nematodes), and resistance breeding (3). Genetic traits of wild and cultivated plant species introduced by classical crossings have become the most sustainable instruments to protect plants from viruses. These tools are now being augmented by gene technological engineering. Molecular biology has identified and characterized known resistance genes and created new resistance traits. Classical genetics and molecular biology have developed fruitful interactions and rely on each other for long-lived defense strategies.
