Antiviral Phytoproteins as Biocontrol Agents for Efficient Management of Plant Virus Diseases

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Plant virus diseases have always been of great concern to farmers, researchers and policy makers because they cause enormous yield loss in many cereal, vegetable, fruit, legume and cash crops like cotton. Plant virus diseases are very difficult to control and are much problematic than commonly occurring fungal diseases. Virus infection causes loss by reducing the productive life of the crop e.g. potatoes infected with leaf roll, by adverse effect on vegetative propagation, on germination of seeds and growth of seedlings, by reduction in quality of fruits, by loss of vigour and by number of other usual and unusual ways (Waterworth and Hadidi, 1998). The recent outbreak of cotton leaf curl virus disease in cotton in northern cotton growing region of India has led to huge yield loss of cotton fibre. Approximately 12,000 ha of area under cotton was affected by leaf curl virus disease during 1996 in Rajasthan alone. An annual loss of US $ 300 million is caused by MYMV by reducing the yield of black gram, mungbean and soybean (Varma et al., 1992). It is therefore, important to develop management strategy for virus diseases of important crops so that the losses can be minimised. Viral parasitism is unique, in contrast to fungi and bacteria. Viruses do not attack the structural integrity of their host tissues, but instead they subvert the synthetic machinery of the host cell, acting as molecular pirates. Therefore, the management of virus diseases is a difficult task. Control strategies are mainly aimed at reducing or eliminating existing sources of infection, prevention of virus transmission, etc. The development of methods of virus disease control, continue to be vital elements in the drive to improve crop productivity. The use of molecular genetic techniques has provided new insights into how plants defend themselves against pest attack.