Search Results (6)

Flavescence dorée (FD) is the most important phytoplasma-associated disease of the grapevine yellows complex in Europe. Recent studies highlighted a great genetic diversity within FD phytoplasma (FDp) strains and demonstrated that their diffusion is not related exclusively to the pathosystem including Vitis vinifera L. and Scaphoideus titanus but involves additional vectors and reservoir plants. This study aimed to investigate FD epidemiology in north-western Italy, with a particular focus on FDp hosts. During field surveys, leaf samples were collected from symptomatic grapevines and other symptomless plant species, and insects were collected within and around vineyards. Phytoplasmas belonging to the ribosomal group 16SrV were detected and typed using nested-PCR-based amplification and nucleotide sequence analyses of the map gene. All symptomatic grapevines were found to be infected by the FDp genotype M54, prevalent in S. titanus and also identified in other known and newly reported hosts. Interestingly, other FDp strains (M38, M50, M51, M121) and FDp-related strains (M39, M43, M48), never detected in grapevines, were largely identified in several known and newly reported host plants and insects including S. titanus. Such evidence confirmed the complexity of FD ecology, expanding the knowledge on the range of FDp host plants putatively involved in the disease spread. Full article

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. Full article

Bois noir, an economically important disease of grapevine yellows that causes significant economic losses in wine production, is associated with ‘Candidatus Phytoplasma solani’ and transmitted to grapevines by cixiids Hyalesthes obsoletus and Reptalus panzeri. Polyphagous planthopper Dictyophara europaea, commonly found in natural habitats, harbors phytoplasmas from distinct groups and is an alternative vector in the open epidemiological cycles of the Flavescence dorée phytoplasma in grapevine in European vineyards. This study addresses the role of D. europaea in the transmission cycle(s) of ‘Ca. P. solani’ among wild habitats, natural reservoir plants, and the vineyard agroecosystem using MLSA and transmission trials with naturally infected adults to grapevine and Catharanthus roseus. The infection rates of D. europaea ranged from 7% to 13% in diverse locations, while reservoir herbaceous plants were infected in the amount of 29%. A total of 13 CaPsol MLSA genotypes were detected in D. europaea (7) and plants (8). Nine of them corresponded to previously identified genotypes. Two new genotypes were found in D. europaea (tuf-b1/S1/V14/Rqg50-sv1 and tuf-b1/S18/V14/Rqg50-sv1) and one in Convolvulus arvensis (tuf-b1/S1/V2-TA/Rqg31-sv1), whereas one was shared by two hosts, Crepis foetida and Daucus carota (tuf-b1/S1/V2-TA/STOL-sv1). Naturally infected D. europaea successfully transmitted the tuf-b1/S1/V2-TA/STOL type to five grapevines and six periwinkles, tuf-b1/S1/V2-TA/Rqg31 to one grapevine, and tuf-b1/S1/V2-TA/Rqg50 to one periwinkle, indicating that D. europaea is an intermediate vector in CaPsol epidemiological cycles. Full article

Flavescence dorée (FD) is a European quarantine disease of grapevine caused by FD phytoplasma (FDp) transmitted by the leafhopper of North American origin Scaphoideus titanus. The disease affects the most important viticultural regions of Europe and all wine-growing regions of Serbia. Unlike the insect vector, the pathogen is native to Europe and associated with several wild host plants among which alder trees as the main source of two out of three map genetic clusters of pathogen variants (Map-FD1 and FD2). Heretofore, the FDp epidemic in Serbian vineyards was thought to be monotypic, i.e., caused by the single genotype of the Map-FD3 cluster, M51, and correlated with clematis as the natural source plant. This study aimed to provide data on genetic diversity, through map and vmpA gene typing, and insights into ecological properties of epidemiological cycles driving the epidemic outbreaks of FD in Serbia today. Map genotyping of 270 grapevine isolates collected from 2017 to 2019 confirmed M51 as autochthonous genotype widespread in all wine producing regions of Serbia and the dominant FDp epidemic genotype in most of the districts (75%, 202/270 isolates), except in north Serbia where multiple outbreaks of M12 Map-FD3 were recorded (54 isolates). Tree of heaven is reported as a new FDp plant reservoir for the Serbian vineyards, hosting the M51 genotype, along with clematis. An outbreak of a new endemic Map-FD3 genotype M144 was documented in grapevine samples from east Serbia (5 isolates), correlating with previous findings of the same genotype in clematis. In addition, single grapevine infections with five new Map-FD3 genotypes (M150-M154) were recorded in central Serbia, thus indicating high endemic potential for new outbreaks. The vmpA typing placed all Map-FD3 isolates into the VmpA-III cluster, i.e., Vectotype III. Finally, we found direct evidence that at least two FDp endemic genotypes, M89 and M148, of the Map-FD2/VmpA-II have escaped from alders and propagated in the grapevine-S. titanus pathosystem in Serbia (Vectotype II). Our findings confirm the high complexity of the FDp ecological cycle and provide evidence of a unique, autochthonous Balkan epidemiology sourced endemically. Full article

Phytoplasma transmission takes place by insect vectors through an Acquisition Access Period (AAP), Latency Period (LP) and Inoculation Access Period (IAP). Generally, phytoplasmas are believed to be transmitted more efficiently by nymphs because they need a long LP to reach the salivary glands before becoming infective. The transmission can start from adults as well, but in this case a long LP may exceed the insect’s lifespan. However, previous evidence has indicated that adults can undergo a shorter LP, even though little knowledge is available regarding the phytoplasma temporal dynamics during this period. Here, we investigate the minimum time required by the phytoplasma to colonize the vector midgut and salivary glands, and finally to be inoculated into a plant. We used the leafhopper Euscelidius variegatus to investigate the life cycle of flavescence dorée phytoplasma (FDP). Phytoplasma-free E. variegatus adults were left on broad beans (BBs) infected with FDP for an AAP of 7 days. Subsequently, they were individually transferred onto a healthy BB for seven different IAPs, each one lasting 24 h from day 8 to 14. Molecular analyses and fluorescence in situ hybridization were performed for FDP detection. FDP was found in the leafhopper midgut from IAP 1 with an infection rate reaching 50%, whereas in the salivary glands it was found from IAP 2 with an infection rate reaching 30%. FDP was also detected in BBs from IAP 4, with infection rates reaching 10%. Our results represent an important step to further deepen the knowledge of phytoplasma transmission and its epidemiology. Full article

Quantitative estimates of vector populations and their infectivity in the wild and in cultivated compartments of agroecosystems have been carried out to elucidate the role of the wild compartment in the epidemiology of Flavescence dorée (FD). Seven sites were selected for the investigations in the Piedmont Region of Italy. They were characterized by a high variety of agricultural and ecological landscape features, and included a vineyard surrounded by wild vegetation. In order to describe abundance and prevalence of FD-infected vectors in the cultivated and wild compartments of the vineyard agroecosystem, adults of Scaphoideus titanus were collected by yellow sticky traps inside and outside the vineyard over the period July 10th–September 9th, 2015. They were counted and singly analyzed for the presence of FD phytoplasmas by PCR. Multifactorial correlations among vector population level, prevalence of infected insects inside and outside the vineyards, disease prevalence in cultivated and wild Vitis plants, and location of wild Vitis plants with respect to the vineyard were analyzed. Abundance of S. titanus adults significantly decreased from the end of July onwards, particularly inside the vineyard (average range 22.7 ± 2.5 insects/trap). Percentage of FD-positive S. titanus was significantly higher outside the vineyard (up to 48% on average) compared to inside the vineyard (up to 34% on average), and increased during the season in both compartments. Full article