Peru is a centre of origin and domestication of the potato, pepper and tomato (family Solanaceae). Many potyviruses (genus Potyvirus) that infect these crops were described 20-30 years ago. However, definitive classification of these viruses as distinct species remains unresolved for several reasons, including their close serological relationships, similar symptomatology in test plants and lack of genomic sequence data. Using samples collected from Peru, we have determined the complete genomic sequence of two strains of Peru tomato virus (PTV) as well as near-complete sequences for two additional PTV strains. We also obtained partial sequences of four strains of Potato virus V (PVV). Comparisons with genomic sequences of Wild potato mosaic virus (WPMV), Potato virus Y (PVY), Pepper mottle virus (PepMoV), Potato virus A (PVA) and other potyviruses established that all these viruses constitute different taxa (species). Phylogenetic comparisons indicated that PTV, PVV and WPMV are the most closely related species which, together with PepMoV, PVY, Pepper yellow mosaic virus and Pepper severe mosaic virus, constitute a group that is distinguishable from other potyviruses. Therefore, the members of this group may share a common ancestor. PVA does not belong to this group. PVV and PTV were also closely related serologically. However, PTV did not cross-protect against PVV and WPMV in tobacco plants or complement systemic infection of PVV and WPMV in pepper plants. Two biologically and phylogenetically distinguishable strain groups were identified within PTV and PVV. In future studies, the sequence data and virus-specific primers and probes for PTV, PVV and WPMV described in this study will enable accurate indexing of plants with respect to either single or mixed infection with these viruses.

The complete genome for a barley isolate of Wheat dwarf virus (WDV) from Tekirdağ, Turkey, WDV-Bar[TR], was isolated and sequenced. The genome was found to be 2739 nucleotides long, which is shorter than wheat-infecting WDV isolates, and with a genome organization typical for mastreviruses. The complete genome of WDV-Bar[TR] showed 83-84% nucleotide identity to wheat isolates of WDV, with the non-coding regions SIR and LIR least conserved (72-74% identity). The deduced amino acid sequences for Rep and RepA were most conserved (92-93%), while CP and MP were less conserved (87% and 79-80%, respectively). The identity to other mastrevirus species was significantly lower. In phylogenetic analyses, the WDV isolates formed a distinct clade, well separated from the other mastreviruses with the wheat isolates grouping closely together. Phylogenetic analyses of WDV-Bar[TR], the partial sequence for another Turkish barley isolate (WDV-Bar[TR2]) and published WDV sequences further supported the division of WDV into two distinct strains. The barley strain could also be divided into three subtypes based on relationships and geographic origin. This study shows the first complete published sequence for a barley isolate of WDV.

Wheat dwarf virus (WDV) causes disease in wheat ( Triticum aestivum ) and barley ( Hordeum vulgare ) in many parts of Europe. The host range also includes many species of the family Poaceae. WDV is only transmitted by the leafhopper Psammotettix alienus . During a five-year period (2001)(2002)(2003)(2004)(2005), grass samples were collected in central Sweden in the vicinity of fields with WDV-infected winter wheat. Screening with ELISA and PCR identified WDV in a low number of samples (8/1098) from only three grass species: Apera spica-venti , Avena fatua and Poa pratensis . In addition, triticale was found to be positive. Fourteen WDV isolates from Avena fatua , Apera spica-venti , Triticum aestivum , Lolium multiflorum , Poa pratensis , triticale and the insect vector Psammotettix alienus , were partially sequenced ( ca. 1200 nucleotides), providing the first published WDV sequences from the insect vector. All isolates belonged to the wheat strain of WDV and the genetic diversity was low. Phylogenetic analyses showed no clear grouping according to geographical location or host species. The results suggest that the same WDV genotypes are infecting both wheat and grasses in Sweden. Interestingly, one group of isolates (subtype B) formed a distinct clade in the phylogenetic tree. Subtype B was always found in mixed infection with the main genotype. Complete sequencing of a subtype B isolate showed that it was 98·6% identical to a typical wheat isolate from the same plant.

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Comparative analysis of the host ranges of the barley and wheat strains of Wheat dwarf virus (WDV; family Geminiviridae; genus Mastrevirus) in Europe has been severely hampered by the lack of an infectious clone of the barley strain. To remedy this situation an agroinfectious clone of a Hungarian isolate of the barley strain (WDV-Bar[HU]) was constructed and its virulence tested in barley (Hordeum vulgare), wheat (Triticum aestivum), rye (Secale cereale) and oat (Avena sativa) by agroinoculation. Although all four species could be systemically infected by the isolate, infections were asymptomatic in the rye and oat cultivars tested. WDV-Bar[HU] induced chlorosis and stunting symptoms typical of WDV in barley, while in wheat low infection rates but high mortality of infected seedlings were observed. In contrast, a much higher percentage of wheat plants agroinoculated with a wheat-strain isolate (WDV- [Enk1