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First Detection of Wheat streak mosaic virus in Two Perennial Weed Species, Agropyron cristatum and Hordeum jubatum subsp. intermedium, in Canada

Bennypaul, H., Abdullahi, I., Harding, M. W., Neeser, C.
Plant disease 2019 v.103 no.6 pp. 1441
Aceria tosichella, Agropyron cristatum, Avena sativa, Echinochloa, Hordeum jubatum, Hordeum vulgare, Panicum, Triticum aestivum, Wheat streak mosaic virus, Zea mays, barley, coat proteins, corn, death, epidemiology, flora, genes, genomics, grass weeds, grasses, growth retardation, millets, nucleotide sequences, oats, perennial weeds, perennials, planting, sequence analysis, surveys, viruses, weed hosts, winter, winter wheat, Alberta, Massachusetts, Mexico, Ontario, Saskatchewan
Wheat streak mosaic virus (WSMV) causes wheat streak mosaic disease, a potentially devastating infection of wheat with a worldwide distribution. WSMV is a positive-sense, single-stranded, monopartite RNA virus in the family Potyviridae. WSMV is vectored by the wheat curl mite (Aceria tosichella Keifer), and seed-transmission has been reported at a very low rate (Jones et al. 2005). This virus infects all varieties of wheat (Triticum aestivum L.), and most isolates of WSMV can infect barley (Hordeum vulgare L.), oats (Avena sativa L.), some varieties of maize (Zea mays L.), millet (Panicum, Setaria, and Echinochloa L. spp.), and a number of grassy weed species (Singh et al. 2018). WSMV is known for causing damage to wheat in western Canada. The most recent outbreak of WSMV in western Canada occurred in southern Alberta and Saskatchewan in 2016 to 2017 (Harding et al. 2017), with some fields showing total crop failure. Typical symptoms of infection are stunting, pale-green to yellow streaking in a mosaic pattern, and fewer and smaller heads. Severe infection can lead to shriveled grains and plant death. Both the wheat curl mite and WSMV can survive the winter on fall-seeded winter wheat, volunteer wheat, and some perennial grasses. Control of living hosts such as volunteer wheat plants and grassy weed hosts at least 2 weeks before planting the new crop of wheat is recommended for managing the diseases (Watkins et al. 1989). Knowledge of the host status of grassy weed species is important for making evidence-based management decisions. More than 40 species of grassy weeds have been reported as host of WSMV (Singh et al. 2018). During the 2017 WSMV survey in Alberta, plants belonging to two species of commonly occurring perennial weeds, crested wheatgrass (Agropyron cristatum [L.] Gaertn.) and foxtail barley (Hordeum jubatum subsp. intermedium Bowden), were sampled from the edges of a WSMV-positive wheat field. Morphological identities of both weed species were confirmed using description and keys available in the Flora of North America North of Mexico (Barkworth 2007; Bothmer et al. 2007). Weed samples were tested for WSMV by polymerase chain reaction targeting amplification of 144-bp NIb-specific fragment using primers WS5-7750 (5′-CTTATCAATGCCGACACAAAGGA-3′) and WS3-7895 (5′-GCTTCATGAATGTGTGTGACATGTA-3′) (Schubert et al. 2015). Out of four crested wheatgrass plants and two foxtail barley plants, one plant of each weed species was found to be infected with WSMV. As a further confirmation, whole coat protein (CP) gene was amplified from the positive samples using primers WSMV-CP-AM-F2 (5′-CTGGGACCCGAACGGATTTAG-3′) and WSMV-CP-AM-R (5′-GCTCACGCAAGAGCGTTTAC-3′) and cloned in pMiniT vector (New England Biolabs, Ipswich, MA). Cloned inserts were sequenced at The Centre for Applied Genomics (Toronto, ON, Canada). BLASTN analysis of the obtained CP gene sequences showed ≥98% sequence identity to CP gene sequences of WSMV isolates CK93 (AF511598), WO93 (AF511644), and KY0083SV (AF511624) present in NCBI nucleotide database. A. cristatum has been previously reported to be immune to WSMV (Slykhuis 1952). More recent surveys of grassy weeds either did not detect (Ito et al. 2012) or rarely detected WSMV in A. cristatum (Brey 1998). This is the first report of WSMV detection in A. cristatum in Canada. H. jubatum has been listed as nonhost to WSMV (http://www.dpvweb.net/dpv/showdpv.php?dpvno=393). To the best of our knowledge, this is the first report of detection of WSMV from H. jubatum subsp. intermedium. Further studies are needed to evaluate the role of these weed species in WSMV epidemiology under Canadian growing conditions.