Recombinant DNA technology or genetic engineering ushered in a new era in the study of plant viruses. The major breakthrough came in the 1980s, primarily due to the development of new methods for RNA reverse transcription and cDNA cloning, along with restriction enzyme mapping and rapid nucleotide sequencing. An information explosion in various molecular aspects of plant viruses was caused by these studies. 1990s research efforts investigate the study of viral genomes, genetic maps, genes and gene expression, gene products, and genetic basis of virus functions and biological properties. This text analyzes, collates and reviews such genetic variability; brings out the molecular basis of virus transport in plants and of virus transmission by vectors and of disease symptomatology; and discusses molecular biology of viroids and transgenic plants. It also treats the recently discovered genetic phenomenon of gene silencing and the gene-for-gene interactions between the hosts and plant viruses. biological properties.