Wheat streak mosaic virus (WSMV—Potyviridae, Tritimovirus), transmitted by the eriophyid mite Aceria tosichella Keifer (Acari: Eriophyidae), was considered a quarantine pest in South America. Since the first report of virus in Argentina, the vector has been found in Argentina, Uruguay and Brazil. The objective of this work was to determine the occurrence of WSMV in Brazil and characterize isolates from wheat-growing areas. Between 2009 and 2011, a total of 40 samples collected in wheat (Triticum aestivum) growing areas, where the presence of the mite was previously related, were tested by RT-PCR for virus detection. Six isolates of WSMV were obtained and characterized by sequencing. Two of them had their host range determined. The Brazilian WSMV isolates clustered in clade D are closely related to the Argentine isolate Arg2 (FJ348359). As expected, isolates were unable to infect dicotyledons plants. They caused mosaic in Triticum aestivum, Hordeum vulgare, Secale cereale, ×Triticosecale, and Zea mays, and they were also able to infect Avena sativa. The presence of WSMV in wheat-growing areas of the Brazilian state Rio Grande do Sul was confirmed, possibly having been introduced from a common source and/or direct vector bearing virus migration from Argentina. 1. Introduction Wheat streak mosaic virus (WSMV) is the type species of genus Tritimovirus in the family Potyviridae [1]. First reported, in 1929, in the Central Great Plains of the USA [2], currently it is common in most major wheat-growing regions of the world. WSMV is transmitted by eriophyid mite Aceria tosichella Keifer (Acari: Eriophyidae) [3], and low rates of seed transmission have been reported [4–6]. The virus infects several plant species of the family Poaceae [7, 8], causing severe mosaic, stunting, and necrosis. WSMV is considered the most important virus disease of North America, Europe, Oceania, and Middle East wheat-growing regions [3]. Annual production losses were frequently observed, in some instances severe local WSMV infection could result in yield losses up to 100% [5, 9, 10]. Divergent strains of WSMV occur in the USA, Mexico and Eurasia [7, 11, 12], and WSMV isolates, similar at those found in American Pacific Northwest (APNW), were detected in the southern hemisphere [5, 8, 13–15]. Since a decade ago the complex Aceria tosichella and WSMV had not been found in South America, being considered a quarantine pest [3]. However, in 2002, the WSMV was detected in the central area of Cordoba province in Argentina [14], and in 2004 the vector, A. tosichella, was found associated with
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