Impact of co-infection of wheat streak mosaic and Triticum mosaic viruses on transmission rates by the wheat curl mite

Wheat streak mosaic (WSMV) and Triticum mosaic (TriMV) viruses are transmitted by Aceria tosichella Keifer, the wheat curl mite (WCM), to cereals worldwide.  In the Great Plains, WSMV is more prevalent than TriMV, but co-infection is frequently observed. WSMV and TriMV show increased disease severity when co-infected.  Previous work has shown that different mite genotypes are able to transmit TriMV at different rates.  Our objective was to determine the virus transmission rates when WSMV and TriMV were co-infected. We used Type 2 WCM, to determine virus transmission rates for mock, WSMV, TriMV and double inoculations.  Virus source plants were inoculated, infested with WCM, and allowed to build up for 3 weeks. Individual mites from each source plant were transferred to each of 10 test plants. Virus transmission was determined by ELISA assays for all source and test plants. Twelve replicates of each treatment were used 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. We also compared Type 1 and Type 2 WCM to assess if the relationship of co-infection on transmission rates were the same among mite genotypes.  For this experiment only double infected and mock source plants were used. Type 1 mites do not transmit TriMV, but they vary in rates of transmission for WSMV. These findings help in our understanding of the epidemiology of the WCM virus complex.