Department of Plant Molecular Biology, University of Delhi South Campus, New Delhi-110021.
Abstracts of Research Papers Presented during the National Symposium of Indian Virological Society at Unit of Plant Virology, Division of Plant Pathology, Indian Agricultural Research Institute, New Delhi-110 012, October 14–1.
Cassava (Manihot esculenta) is a tropical root crop grown extensively in southern states of India and is used as source of edible and industrial starch. Cassava Mosaic Disease (CMD) is common among field-grown cassava in India and is believed to be caused by the geminivirus Indian cassava mosaic virus (ICMV). To look for other causative viruses which may be responsible for CMD in India, an extensive programme of cloning and sequencing of PCR-amplified full-length geminiviral DNAs, associated with CMD was initiated. Analysis of several geminiviral clones from CMD-affected cassava plants revealed that in addition to being strains of ICMV, some of them were strains of Sri Lankan cassava mosaic virus (SLCMV), a geminivirus earlier reported from only Sri Lanka. The infectivities of these cloned viral DNAs were checked on both the experimental host Nicotiana benthamiana by mechanical and biolistic inoculation and the natural host cassava by biolistic inoculation. A majority of the clones were infectious as they induced typical symptoms of ICMV infection on N. benthamiana, which was confirmed by appropriate DNA analysis from systemic leaves of inoculated plants. One set of SLCMV clones, both originating from the same cassava plant, gave rise to mild symptoms on cassava, six months following inoculation. The viral genes involved in movement-related functions were further studied by transiently expressing them as fused versions with the fluorescent protein GFP in detached leaves of N. benthamiana and cassava. Intracellular localization of the above fluorescently-tagged proteins and their deleted versions helped to tentatively assign domain functions to the above proteins, which are involved in peripheral localization, nuclear localization and other functions.
One major disease of rice in south and southeast Asia is tungro, caused by the simultaneous infection of rice with Rice tungro spherical virus (RTSV), member of the family Sequiviridae, Genus Waikavirus and Rice tungro bacilliform virus (RTBV), member of the family Caulimoviridae, Genus RTBV-like. Over the last several years, we have cloned and analyzed RTBV and RTSV genomes from different regions of India. Our analysis suggests that RTBV genomes in India show significant variation from those reported from various countries of south-east Asia. On the other hand, RTSV genomes from India strongly resemble those from South-east Asia. Their evolutionary relationships and the possible effect of the deployment of transgenic resistance against tungro in our country will be discussed.
