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The genus Arsenophonus (Gammaproteobacteria) is comprised of intracellular symbiotic bacteria that are widespread across the arthropods. These bacteria can significantly influence the ecology and life history of their hosts. For instance, Arsenophonus nasoniae causes an excess of females in the progeny of parasitoid wasps by selectively killing the male embryos. Other Arsenophonus bacteria have been suspected to protect insect hosts from parasitoid wasps or to expand the host plant range of phytophagous sap-sucking insects. In addition, a few reports have also documented some Arsenophonus bacteria as plant pathogens. The adaptation to a plant pathogenic lifestyle seems to be promoted by the infection of sap-sucking insects in the family Cixiidae, which then transmit these bacteria to plants during the feeding process. In this study, we define the specific localization of an Arsenophonus bacterium pathogenic to sugar beet and strawberry plants within the plant hosts and the insect vector, Pentastiridius leporinus (Hemiptera: Cixiidae), using fluorescence in situ hybridization assays. Phylogenetic analysis on 16S rRNA and nucleotide coding sequences, using both maximum likelihood and Bayesian criteria, revealed that this bacterium is not a sister taxon to "Candidatus Phlomobacter fragariae," a previously characterized Arsenophonus bacterium pathogenic to strawberry plants in France and Japan. Ancestral state reconstruction analysis indicated that the adaptation to a plant pathogenic lifestyle likely evolved from an arthropod-associated lifestyle and showed that within the genus Arsenophonus, the plant pathogenic lifestyle arose independently at least twice. We also propose a novel Candidatus status, "Candidatus Arsenophonus phytopathogenicus" novel species, for the bacterium associated with sugar beet and strawberry diseases and transmitted by the planthopper P. leporinus.

The efficiencies of two published primer pairs (RSP13-RSP14 and RSP2-RSP21) were compared in reverse transcriptionpolymerase chain reaction (RT-PCR) to improve the diagnosis of Grapevine rupestris stem pitting-associated virus (GRSPaV), which has consistently been found associated with rupestris stem pitting (RSP), one of the most common infectious diseases of grapevine. Fifty-six grapevine accessions from different locations in Northern Italy were tested. Of these, 48 were positive with primers RSP13-RSP14 and 37 with primers RSP2-RSP21, suggesting that primer pair RSP13-RSP14 has a broader detection spectrum than primers RSP2-RSP21. The coat protein (CP) gene was also amplified by RT-PCR and the amplicons analysed by single-strand conformation polymorphism (SSCP) and sequencing. The results support the existence of wide variability within this virus, independent of cultivar or geographic origin. Sequence analysis of the 17 Italian GRSPaV isolates examined showed a molecular identity ranging from 78AE8 to 99AE7%, within which, four groups of sequence variants were recognized. Flexuous rod-shaped particles, approximately 800 nm in length, were detected in plant extracts from infected grapevines and were positively decorated with the specific antiserum As7-276 in immunosorbent electron microscopy (ISEM). This is the first report of GRSPaV particles in grapevines observed by transmission electron microscopy (TEM) in Italy.

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