Transmission of Soil-borne Barley Yellow Mosaic Virus

Abstract

Two-rowed barley plants grown on autoclaved soil showed infection when mechanically inoculated on leaves with soil-borne barley yellow mosaic virus. Test seedlings grown on this soil or autoclaved soil containing the roots of these infected plants failed to produce infection.A drench of Dexon** at a concentration of 70-140ppm on drill furrows of infected fields immediately before sowing brought about a considerable decrease in the disease incidence. On the other hand, the infectivity of diseased leaf juice was not affected by the addition of Dexon to the juice at concentrations of 50-200ppm in mechanical inoculations.Naturally infected roots were homogenized and filtered through 325 mesh screen. The filtrate was found to contain a high concentration of resting spores of Polymyxa graminis Led., and showed infectivity when inoculated to soil. The infectivity was lost at a dilution of 1:102.Naturally infected roots stored in refrigerator (4°C) for 4 months were immersed in tap water in petri dishes at 13-15°C. The water was changed daily. Infectivity of this water was tested by soaking germinated barley seeds in it, and was found to be infective from the 4th day after root immersion. A considerably high infectivity persisted until the 15th day. The infectivity of the water became higher when infected roots were kept in wet soil at 23°C for more than two weeks before immersion.The number of zoospores mostly of P. graminis released on successive days after the roots were immersed was found to be closely correlated with the infectivity of the water.From these results, P. graminis is suspected to be a vector of this virus.