Identification of Wheat Spindle Streak Mosaic Virus and Its Role in a New Disease of Winter Wheat in Kansas

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Abstract
Severe mosaic, yellowing, bronzing, and stunting symptoms in patterns typical of the Polymyxa graminis-vectored wheat soilborne mosaic virus (WSBMV) appeared in early March 1984 and again in the spring of 1985 in south central Kansas. Many of the hard red winter wheat cultivars showing symptoms were considered resistant to WSBMV. Electron microscopic examination revealed WSBMV particles and other long, flexuous rods. Examination of thin sections revealed pinwheel and amorphous inclusion bodies. From these observations and with Western blot analysis, it was determined that the plants were also infected with wheat spindle streak mosaic virus (WSSMV). WSBMV and WSSMV particles were observed in all symptomatic plants in a ratio of about 20:1, respectively. A comparison of wheat plants resistant to wheat soilborne mosaic (WSBM) in soils infested with WSBMV and WSBMV plus WSSMV indicated that WSBMV infected WSBM-resistant cultivars and increased to about the same levels as in WSBM-susceptible cultivars in the presence of a WSSMV infection. Environmental conditions during the springs 1984 and 1985 were optimal for wheat spindle streak mosaic (WSSM) symptom development. The sudden recognition of this disease is attributed to several new WSBM-resistant cultivars that show vivid symptoms when infected with WSBMV plus WSSMV and the conducive environmental conditions. WSSM has not been shown to be widely distributed throughout the eastern half of Kansas and, in many cases, WSSM entirely overlaps in range with WSBM.