AGROPYRON MOSAIC AS A DISEASE OF WHEAT IN CANADA

Abstract

Agropyron mosaic virus (AMV) is common on Agropyron repens (L.) Beauv. in southern Ontario and Quebec and has been found on Prince Edward Island and in southeastern Saskatchewan. It was also found on a few winter wheat plants in many fields in southern Ontario each year since 1957, and on spring wheat in Saskatchewan in 1961. AMV has not appeared to be economically important, but the occasional high incidence of infection in wheat near diseased A. repens and the fact that infected plants were sometimes severely stunted have indicated that it could be important under favorable conditions.Wheat was more susceptible than A. repens, or any of the other hosts tested. Usually all wheat plants became infected when inoculated with sap of diseased plants diluted 1:64, and 50% became infected with dilutions of 1:256. Symptoms appeared in 6 days at temperatures of 20° and 25 °C, but were most pronounced at 15 °C. No symptoms developed on wheat kept at 10° or 35 °C for 19 days after inoculation, but sap from these plants was infectious.All isolates of AMV obtained from A. repens and most from naturally diseased wheat caused only mild symptoms on wheat, but some isolates from wheat caused severe chlorosis and stunting. In field tests, manual inoculation with severe isolates reduced yields of spring wheat 25% to 75%, and of winter wheat up to 42%. Up to 100% of the winter wheat plants in small plots sown near naturally diseased wheat during June to late August became infected, illustrating that AMV can be perpetuated on immature wheat. Less infection developed in plots sown in September or later.Eriophyid mites, including Aceria tulipae (K.), Abacarus hystrix (Nal.), and Vasates mckenziei K. were present on naturally diseased plants, but none of these mites has been proved a vector of AMV.