Wheat streak mosaic virusin Australia: Relationship to Isolates from the Pacific Northwest of the USA and Its Dispersion Via Seed Transmission

Abstract

Wheat streak mosaic virus (WSMV) was found for the first time in Australia in 2002. It subsequently was found widely dispersed around the continent and was shown to be seedborne in wheat. The coat protein (CP) gene sequences of nine WSMV isolates from eastern and southwestern Australia are reported, one obtained directly from infected wheat seed, three from seedlings grown from infected wheat seed, and five from infected wheat plant samples. These sequences were compared with those of 66 WSMV CP sequences, including eight previously sequenced Australian isolates. All 17 Australian sequences formed a closely knit monophyletic cluster as part of the D1 subclade of WSMV previously only reported from the Pacific Northwest of the United States. The close phylogenetic relationships of these sequences indicate that the Australian outbreak arose from a single incursion, the source of which appears to be the Pacific Northwest. Three Australian CP sequences were identical, one from the location of the post-entry quarantine facility at Tamworth, New South Wales, and two from seed that had originally been propagated at that facility. These three sequences were closest to the Pacific Northwest sequences and differed from them by as little as eight nucleotides (0.76%). The sequence of a third seedborne isolate originally from the same source differed from the other two seedborne isolates by two nucleotides, indicating that the immigrant WSMV population may have been variable. The other Australian sequences differed from the three identical ones by only one to four nucleotides. The phylogenetic pattern and small number of nucleotide differences between individual isolates from different geographic locations fit the scenario that the virus was introduced once in seed of wheat breeding material, multiplied where it was introduced, and then was dispersed over long distances around the Australian continent along standard distribution routes for wheat breeding lines, germ plasm, and crop seed. These conclusions provide a cautionary tale indicating the importance of effective monitoring of imported plant materials for exotic virus diseases during post-entry quarantine.

Wheat streak mosaic virus genotypes introduced to Argentina are closely related to isolates from the American Pacific Northwest and Australia

“…Furthermore, absence of data does not demonstrate that this lineage was not present in other locations that could have served as a source. With respect to the second explanation, WSMV isolates from Australia are seed borne at 0.5-2% [2,11], a rate several log units greater than that previously reported for WSMV in maize [9]. However, as other Presented is a neighbor-joining tree based on 1,000 bootstrap iterations and rooted with the complete sequence of oat necrotic mottle virus (ONMV) designated as the outgroup.…”

“…Analysis of 3 0 -proximal partial nucleotide sequences [2] indicated that Australian isolates of WSMV were closely related to each other, and also to certain Clade D isolates from the American Pacific Northwest (APNW). As several of the Australian isolates are seed borne in wheat at low frequency [2,11], infected seed has been implicated as the means of initial introduction. Subsequent spread of WSMV within Australia was likely due to both seed transmission and vector transmission by the wheat curl mite [8].…”

Rice Yellow Mottle Virus , an RNA Plant Virus, Evolves as Rapidly as Most RNA Animal Viruses

“…Molecular studies have enlarged the scope of plant virus epidemiology (17,21,31). Recently, renewed attention has been paid to ecological studies dealing with topics such as plant viruses in wild ecosystems, virus spread from wild to cultivated plants, virus emergence, and host plant domestication or movement (5,16,23,29,40). The resulting ecological and epidemiological scenarios are related to plant virus history or even prehistory.…”

Remote Monitoring of Wheat Streak Mosaic Progression Using Sub-Pixel Classification of Landsat 5 TM Imagery for Site Specific Disease Management in Winter Wheat

“…Symptom severity also depends on wheat cultivar, time of infection, temperature, and other environmental conditions that affect vector populations and plant growth [14]. Since its first discovery in 1922 in Nebraska, WSMV has periodically caused severe epidemics, across most of the Great Plains of the United States [3,8,15]. In the Texas Panhandle, much of the wheat is grown as a dual purpose crop, for both winter forage and grain production [10,12].…”