Search

Simple Summary: Flavescence dorée (FD) is a serious disease of grapevine, spread in Europe and caused by phytoplasmas. They are uncultivable bacteria, transmitted from plant to plant by hemipteran insects (mainly leafhoppers) and classified according to their genetic traits. Two different phytoplasma strains are associated with the disease, namely FD-C and FD-D. The former outcompetes the latter during the infection of an experimental plant host (periwinkle), although the latter is more abundant in vineyards. Mixed infections are rare in the field. Here, competition between FD-C and FD-D pathogen strains was investigated during the infection of the laboratory insect vector Euscelidius variegatus (Hemiptera: Cicadellidae). Although insects were forced to acquire both strains, single infection, irrespective of the strain type, was more frequent than expected, probably due to competition among strains. Management of the disease mainly relies on the use (compulsory in some European areas) of insecticides, with evident undesirable effects on the environment and public health. Deciphering mechanisms regulating the epidemiology of FDp strains may pave the way towards the integrated management of the disease, such as by fine-tuning the treatments and identifying mild suppressor strains to outcompete the severe ones. Phytoplasmas are plant pathogenic wall-less bacteria transmitted in a persistent propagative manner by hemipteran insects, mainly belonging to the suborder Auchenorrhyncha (Fulgoromorpha and Cicadomorpha). Flavescence dorée (FD) is a quarantine disease of grapevine, causing great damage to European viticulture and associated with phytoplasmas belonging to 16SrV-C (FD-C) and -D (FD-D) subgroups. FD-C and FD-D strains share similar pathogenicity, but mixed infections are rare in nature. To investigate the competition among FDp strains, specimens of the laboratory vector Euscelidius variegatus (Hemiptera: Cicadellidae) were forced to acquire both phytoplasma haplotypes upon feeding on FD-C- and FD-D-infected plants or after the injection of both strains. The pathogen colonization of insect bodies and heads was monitored with multiplex qPCR, and the efficiencies of phytoplasma transmission were estimated. Single infection, irrespective of strain type, was more frequent than expected, indicating that competition among FD strains occurs. Hypotheses of competition for resources and/or host active sites or the direct antibiosis of one strain against the other are discussed, based on the genetic complexity of FDp populations and on the high genome variability of the FD-D strain. As FD management still mainly relies on insecticides against vectors, the characterization of FDp haplotypes and the description of their epidemiology also have practical implications. [ABSTRACT FROM AUTHOR]

Flavescence dorée (FD) is a threat for wine production in the vineyard landscape of Piemonte, Langhe-Roero and Monferrato, Italy. Spread of the disease is dependent on complex interactions between insect, plant and phytoplasma. In the Piemonte region, wine production is based on local cultivars. The role of six local grapevine varieties as a source of inoculum for the vector Scaphoideus titanus was investigated. FD phytoplasma (FDP) load was compared among red and white varieties with different susceptibility to FD. Laboratory-reared healthy S. titanus nymphs were caged for acquisition on infected plants to measure phytoplasma acquisition efficiency following feeding on different cultivars. FDP load for Arneis was significantly lower than for other varieties. Acquisition efficiency depended on grapevine variety and on FDP load in the source plants, and there was a positive interaction for acquisition between variety and phytoplasma load. S. titanus acquired FDP with high efficiency from the most susceptible varieties, suggesting that disease diffusion correlates more with vector acquisition efficiency than with FDP load in source grapevines. In conclusion, although acquisition efficiency depends on grapevine variety and on FDP load in the plant, even varieties supporting low FDP multiplication can be highly susceptible and good sources for vector infection, while poorly susceptible varieties may host high phytoplasma loads. [ABSTRACT FROM AUTHOR]

Scaphoideus titanus (Hemiptera: Cicadellidae) is the natural vector of Flavescence dorée phytoplasma, a quarantine pest of grapevine with severe impact on European viticulture. RNA interference (RNAi) machinery components are present in S. titanus transcriptome and injection of ATP synthase β dsRNAs into adults caused gene silencing, starting three days post injection (dpi) up to 20 dpi, leading to decrease cognate protein. Silencing of this gene in the closely related leafhopper Euscelidiusvariegatus previously showed female sterility and lack of mature eggs in ovaries. Here, alteration of developing egg morphology in S. titanus ovaries as well as overexpression of hexamerin transcript (amino acid storage protein) and cathepsin L protein (lysosome proteinase) were observed in dsATP-injected females. To evaluate RNAi-specificity, E.variegatus was used as dsRNA-receiving model-species. Different doses of two sets of dsRNA-constructs targeting distinct portions of ATP synthase β gene of both species induced silencing, lack of egg development, and female sterility in E. variegatus, indicating that off-target effects must be evaluated case by case. The effectiveness of RNAi in S. titanus provides a powerful tool for functional genomics of this non-model species and paves the way toward RNAi-based strategies to limit vector population, despite several technical and regulatory constraints that still need to be overcome to allow open field application. [ABSTRACT FROM AUTHOR]

Insect vectors transmit viruses and bacteria that can cause severe diseases in plants and economic losses due to a decrease in crop production. Insect vectors, like all other organisms, are colonized by a community of various microorganisms, which can influence their physiology, ecology, evolution, and also their competence as vectors. The important ecological meaning of bacteriophages in various ecosystems and their role in microbial communities has emerged in the past decade. However, only a few phages have been described so far in insect microbiomes. The leafhopper Euscelidius variegatus is a laboratory vector of the phytoplasma causing Flavescence dorée, a severe grapevine disease that threatens viticulture in Europe. Here, the presence of a temperate bacteriophage in E. variegatus (named Euscelidius variegatus phage 1, EVP-1) was revealed through both insect transcriptome analyses and electron microscopic observations. The bacterial host was isolated in axenic culture and identified as the bacterial endosymbiont of E. variegatus (BEV), recently assigned to the genus Candidatus Symbiopectobacterium. BEV harbors multiple prophages that become active in culture, suggesting that different environments can trigger different mechanisms, finely regulating the interactions among phages. Understanding the complex relationships within insect vector microbiomes may help in revealing possible microbe influences on pathogen transmission, and it is a crucial step toward innovative sustainable strategies for disease management in agriculture. [ABSTRACT FROM AUTHOR]

Flavescence dorée phytoplasmas (FDp, 16SrV-C and -D) are plant pathogenic non-cultivable bacteria associated with a severe grapevine disease. The incidence of the two reference strains on cultivated grapevines is unbalanced, and mixed infections are rare. To investigate the interaction between the two strains, Catharanthus roseus plants were graft-infected with both strains, either simultaneously or sequentially. Different combinations of lateral and apical grafting were applied to avoid possible benefits due to graft position. The infection was monitored for four months through a new diagnostic protocol developed for differentiation and relative quantification of the two strains. Regardless of the temporal or spatial advantage at grafting, FD-C generally outcompeted FD-D. The prevalence of FD-C increased over time and, at the end of the experiment, FD-C was the unique strain detected in the aerial part and the roots of 74% and 90% of grafted plants, respectively. These data indicate that the interaction between the two strains results in competitive exclusion. Understanding the bases of the competition between FD-C and FD-D may contribute to explain the biology of the coexistence of different FDp strains under field conditions, aiming at identifying potential suppressor strains, which can provide alternative and environmentally sustainable solutions for FD control. [ABSTRACT FROM AUTHOR]

Flavescence dorée (FD) is a quarantine grapevine disease caused by a phytoplasma transmitted by the leafhopper Scaphoideus titanus Ball. FD management relies on compulsory insecticide treatments, roguing of infected plants, and substitution with certified material. Some grapevine cultivars show a spontaneous remission of symptoms (recovery). To determine if recovery is a suitable strategy to co-exist with disease in areas of strong infestation, the qualitative aspects of grapes, musts, and wines obtained from recovered Barbera and Chardonnay grapevines were investigated in two productive vineyards. Following field observations, about 1500 plants in each vineyard were divided into healthy (asymptomatic and negative in phytoplasma molecular diagnosis) and recovered (asymptomatic the year of observation but infected the year before). Maturation curves and microvinification tests followed by oenological and sensory analyses showed that maturation trends of recovered grapes were in line with those from healthy plants and the final qualities of wines were comparable. The spread of FD has strongly increased in Piedmont (Italy) in recent decades. Management strategies to cope with the disease are necessary to preserve traditional wine production. Despite the yield from recovered grapevines is quantitatively lower than that from healthy ones, we showed here that the wine quality is, however, preserved. [ABSTRACT FROM AUTHOR]

(1) Background: The leafhopper Scaphoideus titanus is the primary vector of Flavescence dorée phytoplasma (FDp) in European vineyards. Flavescence dorée is one of the most severely damaging diseases of Vitis vinifera and, consequently, a major threat to grape and wine production in several European countries. Control measures are compulsory, but they mainly involve large-scale insecticide treatments, with detrimental impacts on the environment. One possible solution is to exploit the largely unexplored genetic diversity of viruses infecting S. titanus as highly specific and environmentally benign tools for biological control. (2) Methods: A metatranscriptomic approach was adopted to identify viruses that may infect individuals caught in the wild in both its native (United States) and invasive (Europe) areas. Reverse transcription PCR was used to confirm their presence in RNA pools and explore their prevalence. (3) Results: We described nine new RNA viruses, including members of "Picorna-Calici", "Permutotetra", "Bunya-Arena", "Reo", "Partiti-Picobirna", "Luteo-Sobemo" and "Toti-Chryso" clades. A marked difference in the diversity and abundance of the viral species was observed between the USA population and the European ones. (4) Conclusions: This work represents the first survey to assess the viral community of a phytoplasma insect vector. The possibility to exploit these naturally occurring viruses as specific and targeted biocontrol agents of S. titanus could be the answer to increasing demand for a more sustainable viticulture. [ABSTRACT FROM AUTHOR]