Abstract
Barley plants showing yellow dwarf symptoms were found in the barley fields at Nagaoka, Niigata Prefecture in May, 1980. The causal agent was transmitted in a persistent manner by Rhopalosiphum padi to gramineous plants but neither R. maidis nor Schizaphis graminum. Cereals such as barley, wheat, rye and oat exhibited typical yellow dwarf symptoms of stunting and either yellowing or red leaf discoloration. Other plants such as rice, maize, sorghum, Japanease millet, Job's tears and Italian ryegrass showed no symptoms but proved to be symptomless carriers of the agent. Partially purified preparations containing small spherical virus particles about 25nm in diameter were infectious when they were fed by aphids through membranes and the inoculated plants showed typical symptoms caused by barley yellow dwarf virus. Thermal inactivation point of the agent was between 65 and 70C. In the ultrathin sections, electron dense virus-like particles about 22nm in diameter were found only in phloem tissues of affected barley. Based on these results, the causal agent of the disease was identified as barley yellow dwarf virus.
