DIFFERENTIATION OF AGROPYRON MOSAIC, WHEAT STREAK MOSAIC, AND A HITHERTO UNRECOGNIZED HORDEUM MOSAIC VIRUS IN CANADA

Abstract

Agropyron mosaic virus (AMV) from Ontario and wheat streak mosaic virus (WSMV) from Alberta readily infected wheat (Triticum aestivum L.) causing mosaic symptoms that could be differentiated only when carefully compared. All isolates of AMV infected Agropyron repens (L.) Beauv. but not oats (Avena sativa L.). WSMV infected oats but not A. repens. Hordeum mosaic virus (HMV) from Alberta caused mottle rather than streak symptoms on wheat, rye, and other common hosts of WSMV, and did not infect A. repens, but, like AMV, it was not transmitted by Aceria tulipae (K.), the vector of WSMV. It infected Hordeum jubatum L., which is not susceptible to AMV or WSMV. It ranked between AMV and WSMV in longevity and tolerance to heat and pH. The particles were flexuous rods similar to those of WSMV, which appear less flexuous and slightly shorter than particles of AMV.The temperatures at which the viruses multiplied and caused symptoms on wheat ranged from 15° to 33 °C for WSMV and 10° to 30° for AMV. HMV multiplied at all temperatures from 10° to 33 °C but caused symptoms only at 10° to 30 °C.Specific antisera were prepared by partially purifying the viruses by differential centrifugation of juice from diseased wheat, emulsifying the juice with adjuvant, then injecting rabbits intramuscularly. The precipitation titers against their homologous viruses were 1/640, 1/1280, and 1/1280 for the WSMV, AMV, and HMV antisera respectively. The WSMV antiserum did not react with the heterologous viruses, but two HMV antisera had a precipitation titer of 1/16 against AMV, and an AMV antiserum had a titer of 1/10 againt WSMV. Cross absorption of each of the antisera with the heterologous viruses did not reduce the titers against the homologous viruses.The infection of wheat with a mild strain of any of the three viruses protected against later infection by a severe strain of the same virus. Both AMV and HMV were synergistic in combination with WSMV. Serological tests demonstrated that both AMV and HMV multiplied in wheat simultaneously inoculated with both viruses, but systemic infection with either virus protected the plants against later infection by the other.Despite general similarities in physical characteristics and effects on wheat, specific differences in other characteristics show that AMV, HMV, and WSMV are sufficiently different to be designated as different viruses rather than closely related strains of one virus.