Directorate of Rice Research, Hyderabad-500030, India.
Abstracts of the papers presented at the International Conference of Indian Virological Society on “Emerging and Re-emerging viral Diseases of the Tropics and Subtropics” at Indian Agricultural Research Institute, New Delhi, India, December 11–14, 2007.
Four diseases have been reported o n rice that are caused by viruses in India. They include tungro, grassy stunt, ragged stunt and yellow dwarf. Tungro virus is the most important problem in the country. An epidemic outbreak of tungro during 2001 in only three districts of West Bengal caused a paddy or unmilled rice production loss of 0.5 million tonne that amounted to US $ 70 millions. Grassy stunt virus disease causes severe stunting with profuse tillering. The invasion of vector, brown planthopper (Nilaparvata lugens) in rice first appeared in Kerala during 1973–74, when grassy stunt virus appeared and caused heavy yield losses in about 15,000 ha in Trichur and Alleppy districts. Ragged stunt virus (vector, brown planthooper) is found seldom in ratoons, particularly towards crop maturity in fields. Rarely in a few fields, one or two rice hills may be found to be infected with yellow dwarf virus disease. This disease can hardly cause any outbreak due to long incubation period of the pathogen in the vector. The disease is caused by a mycoplasma-like organism - MLO. The infected plants either do not produce any panicles or produce a few small panicles bearing mostly unfilled grains. Nephotettix virescens and N. nigropictus transmit yellow dwarf virus. Based on the magnitude of crop losses, we identify tungro as the research agenda for rice virus research. Primarily it is important to separate the two virus particles from tungro infected tissues and demonstrate the Koch's postulates. Investigations are needed to trace the evolution of exotic RTBV and its integration in rice genome. We need to develop indeigenously ELISA kits and tissue blot immuno assay for the detection of virus particles, especially that of spherical virus. It is also important to reinvestigate on the seed transmission potential, fate of virus particles in plant tissues, virus-vector relationship, helper component in vector, virus suppression, role of alternate hosts, temporal and spatial spread of virus and vector, and perpetuation of tungro virus in nature.
