Impact of wheat streak mosaic and Triticum mosaic viruses on transmission by Aceria tosichella and virus epidemiology

Wheat streak and Triticum mosaic viruses are transmitted by Aceria tosichella Keifer, the wheat curl mite (WCM), to cereals worldwide. In the Great Plains, these viruses greatly impact winter wheat production, resulting in total yield loss in some fields.  Wheat streak mosaic virus (WSMV) is more prevalent in fields than Triticum mosaic virus (TriMV), but co-infection is frequently observed. WSMV and TriMV show a synergistic relation, worsening disease symptoms when co-infected.  Previous work has shown that different mite genotypes are able to transmit TriMV by itself, at different rates.  Using Type 2 WCM, we determined virus transmission rates for mock, WSMV, TriMV and double inoculations.  Virus source plants were inoculated when plants were 21 days old, and one week later, 10 WCM were added to each source plant and mite populations allowed to build up for 2 weeks. Individual mites from each source plant were transferred to each of 10 test plants. Virus transmission was determined by using ELISA assays for all source and test plants. Twelve replicates of each treatment were run for a total of 480 test plants. We found a significant decrease in WSMV transmission when co-infected with TriMV; however, TriMV transmission rates increased when co-infected with both viruses. These findings provide evidence that helps explain the incidence of these two viruses in recent field surveys and will help in our understanding of the epidemiology of this virus complex.