Quantification of Yield Loss Caused byTriticum mosaic virusandWheat streak mosaic virusin Winter Wheat Under Field Conditions

Triticum mosaic virus (TriMV) and Wheat streak mosaic virus (WSMV) infect winter wheat in the Great Plains region of the United States. The two viruses are transmitted by wheat curl mites, which also transmit High Plains virus. In a field study conducted in 2011 and 2012, winter wheat cultivars Millennium (WSMV-susceptible) and Mace (WSMV-resistant) were mechanically inoculated with TriMV, WSMV, TriMV+WSMV, or sterile water at the two-leaf growth stage. Cholorophyll meter (soil plant analysis development [SPAD]) readings, area under the SPAD progress curve (AUSPC), grain yield (= yield), yield components (spikes/m2, kernels/spike, 1000-kernel weight), and aerial dry matter were determined. In cv. Millennium, all measured variables were significantly reduced by single or double virus inoculation, with the greatest reductions occurring in the double-inoculated treatment. Among the yield components, the greatest reductions occurred in spikes/m2. In cv. Mace, only AUSPC was significantly reduced by the TriMV+WSMV treatment in 2012. There was a significant (P ≤ 0.05), negative linear relationship between SPAD readings and day of year in all inoculation treatments in cv. Millennium and in the TriMV+WSMV treatment in cv. Mace. There were significant (P ≤ 0.05), positive linear relationships between yield and SPAD readings and between yield and aerial dry matter in cv. Millennium but not in cv. Mace. The results from this study indicate that under field conditions, (i) cv. Mace, a WSMV-resistant cultivar, is also resistant to TriMV and (ii) double inoculation of winter wheat by TriMV and WSMV exacerbates symptom expression and yield loss in a susceptible cultivar.