Variation of Rice Tungro Viruses: Further Evidence of Two Rice Tungro Bacilliform Virus Strains and Possibly Several Rice Tungro Spherical Virus Variants

Rice tungro disease is caused by two viruses: rice tungro spherical virus (RTSV) and rice tungro bacilhform virus (RTBV). Our results obtained using polymerase chain reaction (for RTBV) and western blot analysis (for RTSV) to study the epidemiology of tungro supported earlier studies that two RTBV strains. South East Asian and Indian, can be differentiated and also better defined the geographic distribution of these two strains. Data on RTSV variation were not so conclusive and consistent as those on RTBV because of the high degree of microvariation of RNA genomes. Our approach for differentiation of RTSV led to three variants being identified, the geographic distribution of which does not correlate with that found for strains of RTBV.