Occurrence and Distribution of Triticum mosaic virusin the Central Great Plains

Byamukama, E., Seifers, D. L., Hein, G. L., De Wolf, E., Tisserat, N. A., Langham, M. A. C., Osborne, L. E., Timmerman, A., and Wegulo, S. N. 2013. Occurrence and distribution of Triticum mosaic virus in the central Great Plains. Plant Dis. 97:21-29. Wheat curl mite (WCM)-transmitted viruses—namely, Wheat streak mosaic virus (WSMV), Triticum mosaic virus (TriMV), and the High Plains virus (HPV)—are three of the wheat-infecting viruses in the central Great Plains of the United States. TriMV is newly discovered and its prevalence and incidence are largely unknown. Field surveys were carried out in Colorado, Kansas, Nebraska, and South Dakota in spring and fall 2010 and 2011 to determine TriMV prevalence and incidence and the frequency of TriMV co-infection with WSMV or HPV in winter wheat. WSMV was the most prevalent and was detected in 83% of 185 season–counties (= s-counties), 73% of 420 season– fields (= s-fields), and 35% of 12,973 samples. TriMV was detected in 32, 6, and 6% of s-counties, s-fields, and samples, respectively. HPV was detected in 34, 15, and 4% of s-counties, s-fields, and samples, respectively. TriMV was detected in all four states. In all, 91% of TriMV-positive samples were co-infected with WSMV, whereas WSMV and HPV were mainly detected as single infections. The results from this study indicate that TriMV occurs in winter wheat predominantly as a double infection with WSMV, which will complicate breeding for resistance to WCM-transmitted viruses. Winter wheat (Triticum aestivum L.) is an economically important crop in the Great Plains of the United States. In 2011, the Great Plains states of Colorado, Kansas, Nebraska, and South Dakota accounted for one-third of the total winter wheat production in the United States (13). Several viruses have been reported to infect winter wheat in this region, resulting in significant economic losses (12,27). They include Wheat streak mosaic virus (WSMV; 17), High Plains virus (HPV; 6), Barley yellow dwarf virus (14), Wheat spindle streak mosaic virus (24); Wheat soilborne mosaic virus (9), and Triticum mosaic virus (TriMV; 20). TriMV was discovered in 2006 in Kansas and subsequently shown to be transmitted by the wheat curl mite (WCM; Aceria tosichella Keifer) (19), which also transmits WSMV and HPV (16,21,23). WSMV and HPV, the two viruses known to be transmitted by WCMs before TriMV’s discovery, are widespread in the Great Plains (8,16). Recent studies have shown that co-infection of wheat with WSMV and TriMV results in synergism that increases symptom severity, elevates titers of both viruses (26), and exacerbates biomass and yield loss (2,28). Therefore, knowing the extent of the distribution of TriMV and the frequency of its co-infection of wheat with WSMV or HPV will assist in estimating the potential risk TriMV poses to wheat production. Recently, field surveys in nine Great Plains states detected TriMV for the first time in Colorado, Montana, Nebraska, North Dakota, Oklahoma, South Dakota, Texas, and Wyoming (1; M. Burrows, personal communication), indicating that the virus is widespread in the Great Plains of the United States. However, information is lacking on the prevalence and incidence of TriMV and the frequency of its co-infection of wheat with WSMV or HPV in individual states in the Great Plains region. The objectives of this study were to (i) conduct detailed wheat surveys in four central Great Plains states (Colorado, Kansas, Nebraska, and South Dakota) to determine the distribution and prevalence of TriMV and (ii) assess the incidence of occurrence of TriMV singly or in double or triple infections with WSMV and/or HPV. Materials and Methods Field surveys. Arbitrarily selected winter wheat fields were sampled in Colorado, Kansas, Nebraska, and South Dakota in spring 2010 and 2011; in Kansas, Nebraska, and South Dakota in fall 2010; and in Kansas and Nebraska in fall 2011 (Tables 1–3). In spring 2011, jointed goatgrass (Aegilops cylindrica Host.) was also collected from an area adjacent to a wheat field that had severe virus symptoms at a location in southwest Nebraska. In the spring, samples were collected from the current year’s winter wheat crop. In the fall, samples were collected from volunteer wheat in fields previously cropped with winter wheat earlier during that year’s growing season. Due to the low probability of finding volunteer wheat, fall sampling was not done in all states over the 2-year period. Fields in up to 31 counties were sampled in each state, and up to three fields were sampled in each county. In each field, up to 50 tillers were arbitrarily selected and collected. Although symptomatic tillers (with leaves showing greenish yellow, parallel, and discontinuous streaks) were targeted for collection, some asymptomatic tillers were collected as well. Symptoms at the field scale ranged from minimal (<1% incidence) to very severe (100% inciCorresponding author: S. N. Wegulo, E-mail: [email protected] Accepted for publication 31 July 2012. http://dx.doi.org/10.1094 / PDIS-06-12-0535-RE © 2013 The American Phytopathological Society