Integrated management of plant viral diseases.

Viral diseases of plants cause enormous economic losses particularly in the tropics and semitropics which provide ideal conditions for the perpetuation of viruses and their vectors. Intensive agricultural practices necessitated by the ever-increasing demands of the rapidly growing population and the introduction of new genotypes, cropping patterns and crops have further aggravated the problem of viral diseases. Many diverse approaches have been tried to minimize the losses caused by these diseases. The approaches are mainly based on avoidance of sources of infection; avoidance or control of vectors; modification of cultural practices; use of resistant varieties obtained though conventional breeding procedures; cross protection; systemic acquired resistance; and use of transgenic plants containing alien genes that impart resistance to viruses. Although the use of resistant varieties has been found to be the most economical and practical, for effective management of viral diseases an integrated approach is essential in sustainable agriculture. Development of integrated management practices also requires correct identification of the causative viruses, because symptoms can be misleading, and adequate understanding of the ecology of viruses and their vectors.