The important rice tungro disease is caused by a complex of two viruses, rice tungro spherical virus (RTSV) which controls leafhopper transmissibility and rice tungro bacilliform virus (RTBV) which causes the severe symptoms. Most of the current control measures are ineffective but there is much hope that non-conventional protection given by transforming rice with virus-related sequences will control the disease. There is increasing understanding of the molecular biology of the RNA genome of RTSV and the DNA genome of RTBV from the type philippine isolate from which strategies for non-conventional protection are being developed. It is important to have information on the variation of the two viruses over the whole region so that conserved sequences can be targetted for non-conventional protection. There is lack of information on virus variation and on that of the leafhopper vector Nephotettix virescens. This project is aimed at gaining this information. The structure of the project is that the three Asian laboratories will study the national variation of the two viruses and of the leafhopper and be linked to two European laboratories, one supporting the work on the two viruses and the other supporting the work on the leafhopper. The European laboratories will also study the regional variation of the viruses and vector. The variation of the two viruses will be studied using molecular techniques. For each virus clones of the isolates will be compared by restriction endonuclease mapping and hybridization leading to a picture of the variation and the strains of the two viruses. Monoclonal antibodies raised against the coat proteins of the two viruses will be assessed for their ability to distinguish strains. Probes made to each strain will be used in a larger field survey to determine the distribution of the strains. To study the variation of the leafhopper the efficacy of three techniques, morphological characterization, enzyme electrophoresis and DNA fingerprinting will be assessed. The most suitable technique will be applied to gaining an understanding of the spatial and temporal variation of the leafhopper in the three Asian countries. The efficiency of different variants of leafhopper at transmitting a range of strains of tungro will be assessed. Bringing the studies of the variation of the viruses and of the leafhopper together should give an insight into the epidemiology of this important disease. Source.