Spissistilus festinus (Say, 1830) (Hemiptera: Membracidae) is a frequent pest of leguminous crops in the Southern United States, and a vector of grapevine red blotch virus. Populations of S. festinus were collected in 2015–2017 from various crops and geographic locations in the United States, and fragments of the mitochondrial cytochrome C oxidase 1 (mt-COI) gene and the nuclear internal transcribed spacer 2 (ITS2) region were characterized by polymerase chain reaction and sequencing. Maximum-likelihood and Bayesian analyses of the mt-COI and ITS2 sequences yielded similar phylogenetic tree topologies, revealing two distinct genetic S. festinus lineages with all of the specimens from California comprising one phylogenetic clade, alongside a single GenBank entry from Arizona, and all specimens from the Southeastern United States comprising a statistically-supported distinct clade, regardless of host and year of collection. The only distinct morphological trait between the two genotypes was a less elevated pronotum in the representative specimens from California, compared to the representative specimens from the Southeastern United States. Since this phenotypic feature is inconspicuous, a diagnostic polymerase chain reaction targeting a variable region of the mt-COI fragment was developed to reliably distinguish between the specimens of the two genotypes of S. festinus and to facilitate their specific identification.
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°Distinct spread of GRBV in CA and NY
Limited information is available on the spread dynamics of grapevine red blotch virus (GRBV, genus Grablovirus, family Geminiviridae) in vineyards. Secondary spread of GRBV was documented in vineyards in California but not in New York. Increase in annual disease incidence (4.8, 0.13, and 0%) was unrelated to the estimated initial source of inoculum at planting (1, 40, and 40%) in the three study vineyards. Limited genetic diversity of GRBV populations in newly infected vines supported localized spread in California vineyards, and suggested the planting material as the primary source of inoculum. Among the community of hemipteran insects visiting two of the three study vineyards, populations of Spissistilus festinus, the vector of GRBV, were absent in the NY vineyard and in one of the CA vineyards. Together our findings illustrate differential disease progress in distinct vineyard ecosystems, and support the elimination of virus inoculum sources as an actionable disease management strategy across vineyards.
°Larissa showed a single amino acid of GFLV modulates disease symptoms
We used a reverse genetics approach to identify residue 802 (lysine, K) of the GFLV strain GHu RNA1-encoded RNA-dependent RNA polymerase (RdRp) as a modulator of vein-clearing symptom development in Nicotiana benthamiana. Mutations to this site abolished (K to G, A,or Q) or attenuated (K to N or P) symptom expression. Noteworthy, residue 802 is necessary but not sufficient for vein clearing, as GFLV-F13 RNA1 carrying K802 remained asymptomatic in N. benthamiana. No correlation was found between symptom expression and RNA1 accumulation, as shown by reverse transcription-quantitative polymerase chain reaction. Structure predictions for the RdRp suggested that residue 802 is flanked by strongly predicted stable secondary structures, including a conserved motif of unknown function (805LLKT/AHLK/RT/ALR814).
°Marc serves as President of ICVG
Congratulations to Marc Fuchs on becoming the 3rd President of the International Council for the Study of Virus and Virus-like Diseases of the Grapevine (ICVG). At the 19th meeting of ICVG in Santiago, Chile April 9-12, 2018, Professor Giovanni Martelli handed the torch to Marc as the next leader of ICVG.
It is a testament to Marc’s commitment to and excellence in grapevine virology research and as a worldwide leader in the field. The members of Fuchs lab are very proud and excited for the future of ICVG! Congratulations, Marc!