Evaluation of susceptibility to wheat streak mosaic virus among small grains and alternative hosts in the Great Plains
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Wheat streak mosaic virus (WSMV), endemic in small grains production areas of the Great Plains, causes yield losses of wheat 2 to 5% annually. Yield loss in individual fields can reach 100%. Control relies on cultural practices to control the vector, the wheat curl mite (Aceria tosichella Keifer, WCM), and the use of resistant or tolerant varieties. WSMV and WCM depend on living tissue for survival and reproduction, including common grassy weeds. Little is known about the relative importance of these weeds as alternative hosts of WSMV. The purpose of these studies was to evaluate the risk of infection with WSMV in commonly grown wheat varieties and various grassy weed species, information useful to understanding WSMV epidemiology and control. Winter wheat, spring wheat and barley varieties in Montana were evaluated in the field by measuring the effect of fall vs. spring inoculation and variety on incidence, symptom severity, and yield components. Winter wheat varieties from five states, and spring wheat and barley varieties from Montana were tested for incidence and absorbance in greenhouse. Fall-inoculated winter wheat had less effect of WSMV inoculation compared to spring-inoculated winter wheat. Yields of spring wheat varieties were largely reduced by WSMV inoculation. There was no correlation between yield and incidence or symptom severity. In greenhouse studies, the highest incidence was observed in varieties from Idaho and Nebraska, whereas the highest relative absorbance was observed in varieties from Montana. In 2008 and 2009, surveys of common grassy weeds were conducted. Grass species from croplands in six states were selected and mechanically inoculated to determine the susceptibility to WSMV. Grassy weeds were also evaluated as a source of WSMV by measuring transmission efficiency with virulifeous WCM. Bromus tectorum was the most prevalent grassy weed and the most frequent viral host. Aegilops cylindrica, and Avena fatua had the highest incidence and relative absorbance. There were no differences in the susceptibility of grass species to WSMV by their state of origin. WCM transmission study indicated infected grass species had lower transmission efficiency than from infected wheat. These studies will benefit producers in Montana to assess their risk of WSMV based on variety selection and the presence of grassy weeds.