Incidence of Wheat Curl Mite-Transmitted Viruses in Major Cereal Crops: Potential Roles of Cover and Forage Cereal Crops in the Continuum of Wheat Streak Mosaic Disease Complex

Wheat streak mosaic disease (WSMD) is the most important viral disease affecting wheat production in the US Great Plains. WSMD is caused by a single or co-infection of wheat curl mite (WCM)-transmitted wheat streak mosaic virus (WSMV), Triticum mosaic virus (TriMV), and/or High Plains wheat mosaic virus (HPWMoV). Nebraska, one of the US Great Plains states, significantly contributes to the national small grain production and utilizes cereal crops as forage and cover crops. In this study, a state-wide sampling was conducted during the 2023-2025 growing seasons across Nebraska to examine the infection dynamics of the causal agents of WSMD in winter and spring cereal crops. A total of 1624 symptomatic leaf samples were assayed with multiplex RT-PCR. In 2024, co-infection of wheat with WSMV and TriMV was more common, whereas WSMV single infections dominated in 2023. In contrast, WSMV single infections were predominant in field oats compared to WSMV-TriMV coinfection. We found a high incidence of WSMV and TriMV as single and co-infections in other cereal and forage crops: rye (80%), triticale (93%), and barley (72%). HPWMoV was found only in a few wheat samples as co-infections with WSMV or WSMV+TriMV in 2023. The P1 and CP sequences of WSMV and TriMV from different cereal hosts showed minimal sequence diversity, indicating that these viruses circulate freely among diverse cereal hosts. Our data suggest that various commercial, forage, and cover cereal crops are infected with mite-transmitted viruses in field conditions and may serve as a green bridge for the continuum of WSMD in wheat.