Effect of wheat curl mite infestation and wheat streak mosaic virus inoculation timing on disease severity in winter wheat

Wheat streak mosaic virus (WSMV) causes average yield losses of approximately 2-3% in winter wheat across the Great Plains. The wheat curl mite (WCM), Aceria tosichella, transmits WSMV along with two other wheat viruses. Severity of diseases caused by viruses is usually influenced by the time of infection and prevailing climatic conditions. The objective of this study was to determine if the timing of infection for WSMV influences disease severity in wheat. In a field study conducted 2013-2014, winter wheat cultivar “Overland” was either mechanically- or mite-infested/inoculated with WSMV at three separate times (early fall, late fall and early spring). Chlorophyll meter (SPAD) readings, grain yield (kg/Ha), number of spikes/m², kernels/spike and 1,000-kernel weight (TKW) were determined. In addition, flag leaf samples were tested for WSMV using ELISA. Grain yield was significantly reduced due WSMV infection (mite infested/inoculated) compared to the non-inoculated control by 87, 31 and 33% in early fall, late fall and early spring treatments respectively. Mechanical inoculation had a significant grain yield reduction of 40% in the early fall inoculation. This is the first known study to use mite infestation to inoculate WSMV under field conditions. The results indicate that timing of virus inoculation has a significant impact on WSMV disease severity and associated yield losses. High WSMV incidences and severe yield reductions could occur if plants are infected in early fall. Management decisions for this disease complex should minimize the potential for early fall mite infestations and virus infection, e.g. control oversummering hosts, avoid early planting.