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Artificial mutations may induce traits that are scarce among natural germplasm sources. This study was conducted to characterize a rice line derived from variety IR64 showing resistance to rice tungro disease (RTD). Approximately 24,000 lines derived from IR64 seeds treated with mutagens were evaluated for reaction to RTD. One of the lines, M4D6 83-1 (MD83), showed enhanced resistance to RTD. MD83 was resistant to rice tungro spherical virus (RTSV) and the virus vector, green leafhopper (GLH; Nephotettix virescens Distant). MD83 was crossed with susceptible varieties IR64 and Taichung Native 1. All F 1 plants were susceptible to RTSV, whereas F 2 and F 3 progenies segregated into resistant and susceptible phenotypes in a 1:3 ratio, indicating that the resistance is controlled by a single recessive locus. Most of the F 3 lines resistant to RTSV were also GLH resistant, suggesting that the resistance to RTSV and GLH was governed by the same locus. It has been difficult to prove whether the genotype MD83 was a product of a mutation event or was represented in the variety IR64 at a very low frequency.