Vector Of Phytoplasma Research Articles

Rainfall and Coconut Accession Explain the Composition and Abundance of the Community of Potential Auchenorrhyncha Phytoplasma Vectors in Brazil

Coconut plantations are attacked by the lethal yellowing (LY), which is spreading rapidly with extremely destructive effects in several countries. The disease is caused by phytoplasmas that occur in the plant phloem and are transmitted by Haplaxius crudus (Van Duzee) (Auchenorrhyncha: Cixiidae). Owing to their phloem-sap feeding habit, other planthopper species possibly act as vectors. Here, we aimed at assessing the seasonal variation in the Auchenorrhyncha community in six dwarf coconut accessions. Also, we assessed the relative contribution of biotic (coconut accession) and abiotic (rainfall, temperature) in explaining Auchenorrhyncha composition and abundance. The Auchenorrhyncha community was monthly evaluated for 1 yr using yellow sticky traps. Among the most abundant species, Oecleus sp., Balclutha sp., Deltocephalinae sp.2, Deltocephalinae sp.3, Cenchreini sp., Omolicna nigripennis Caldwell (Derbidae), and Cedusa sp. are potential phytoplasma vectors. The composition of the Auchenorrhyncha community differed between dwarf coconut accessions and periods, namely, in March and April (transition from dry to rainy season) and August (transition from rainy to dry season). In these months, Oecleus sp. was predominantly found in the accessions Cameroon Red Dwarf, Malayan Red Dwarf, and Brazilian Red Dwarf Gramame, while Cenchreini sp. and Bolbonota sp. were dominant in the accessions Brazilian Yellow Dwarf Gramame, Malayan Yellow Dwarf, and Brazilian Green Dwarf Jequi. We conclude that dwarf coconut host several Auchenorrhyncha species potential phytoplasma vectors. Furthermore, coconut accessions could be exploited in breeding programs aiming at prevention of LY. However, rainfall followed by accessions mostly explained the composition and abundance of the Auchenorrhyncha community.

Molecular detection of phytoplasma from phyllody infected sesame and its vector orosius albicinctus distant

Asymptomatic and symptomatic plants were collected from the phyllody infected sesame field during kharif 2012. From the infected plants, leaves, flowers, stems, seed capsules and roots were selected both from symptoms and symptomless branch. Leafhoppers were also collected from the same field with insect collection net. Total genomic DNA from asymptomatic and symptomatic plants was extracted following CTAB (Cetyl Trimethyl Ammonium Bromide) method with some modifications and from leafhoppers with phenol-chloroform extraction protocol. Amplification of band size 1.8 kb and 1.2 kb was obtained from symptomatic plant and its vector Orosius albicinctus using phytoplasma specific primer pair P1/P7 and R16F2n/R16R2, respectively in first and second round PCR. The phytoplasma could be detected only from stems of symptomless branch of infected plant while in symptomatic plant's branch it was amplified from stem and flower. Thus the status of leafhopper, O. albicinctus as a vector of phytoplasma that cause sesame phyllody was confirmed. Further, it was observed that the symptomless parts of phyllody infected plants also harbour phytoplasma.

New insights on Flavescence dorée phytoplasma ecology in the vineyard agro‐ecosystem in southern Switzerland

AbstractPhytoplasmas associated with Flavescence dorée (FDp) grapevine disease are quarantine pathogens controlled through mandatory measures including the prompt eradication and destruction of diseased plants, and the insecticide treatments against the insect vector, the ampelophagous leafhopper Scaphoideus titanus. In the present study, a multidisciplinary approach has been applied to investigate the FDp ecological cycle in a test vineyard agro‐ecosystem in Canton Ticino, south Switzerland. Despite the scarce population density of S. titanus, a regular trend of new infections (3.4% of the total vines) through the years was observed. The leafhopper Orientus ishidae was found as the most abundant among the captured insect species known as phytoplasma vectors (245 out of 315 specimens). The population of O. ishidae was evidenced prevalently (167 specimens) in the south‐western side of the vineyard and within the neighbouring forest constituted mainly by hazel (Corylus avellana) and willow (Salix spp.). These plant species were found infected by FDp related strains (30% of analysed trees) for the first time in this study. Interestingly, O. ishidae was found to harbour FDp related strains in high percentage (26% of the analysed pools). In addition, 16SrV phytoplasma group was detected for the first time in the insect Hyalesthes obsoletus and a FDp related strain in Thamnotettix dilutior, present in low populations within the test vineyard. Molecular characterisation and phylogenetic analyses of methionine aminopeptidase (map) gene sequences of FDp and related strains, here identified, revealed the great prevalence of the map‐type FD2 in grapevines (97%) and in O. ishidae pools (72%). Such a map‐type was found also in hazel and in T. dilutior, but not in S. titanus. Moreover, map‐types FD1 and FD3 were identified for the first time in Switzerland in several host plants and phytoplasma vectors, including grapevine (FD1), S. titanus (FD1) and O. ishidae (FD1 and FD3). Based on the data obtained in this study, it is reasonable to hypothesise that the ecological cycle of FDp could be related not exclusively to the grapevine‐specific feeding diet of S. titanus, but it could include other insect vector(s) and/or plant host(s). Further studies will be needed to prove the role of O. ishidae as vector able to transmit FDp from wild plants (e.g. hazel) to grapevine.

Diverse phytoplasmas associated with leguminous crops in Russia

A large scale survey of diseased legume plants (mainly clover and alfalfa in the Fabaceae family) was conducted from 2009 to 2013 in four Economic Regions of Russia, Northern (Arkhangelsk and Vologda oblast), Central (Moscow oblast), Volga (Samara oblast) and West Siberian (Novosibirsk oblast). The majority of infected clover plants exhibited symptoms typical of clover phyllody (CPh), clover yellow edge (CYE), or clover proliferation (CP), and infected alfalfa plants exhibited symptoms typical of alfalfa witches’-broom (AWB). Of 161 symptomatic plants from 22 different legume species, 103 tested positive for phytoplasma infection. Phytoplasmas belonging to four groups and six subgroups were detected, of which 31.1% were group 16SrI, with the majority belonging to subgroup 16SrI-C- (causal agent of CPh disease), two belonging to 16SrI-B and two group 16SrI phytoplasmas not identified to the subgroup level;47.6% were group 16SrIII, with the majority belonging to subgroup 16SrIII-B or 16SrIII-B variant (causal agent of CYE disease), and one strain belonging to16SrIII-F; 8.7% were subgroup 16SrVI-A (causal agent of CP and AWB diseases); 9.7% were subgroup 16SrXII-A (causal agent of AWB disease); and 2.9% were mixed infected with subgroups 16SrIII-B and 16SrI-C. The predominant phytoplasma species detected varied by region. In the Northern and Central Regions, the majority of the phytoplasmas detected belonged to subgroups 16SrI-C and 16SrIII-B. In the West Siberian and the Volga Regions, the phytoplasmas predominately detected belonged to subgroups 16SrVI-A and 16SrXII-A, respectively. Subgroup 16SrIII-F was detected in a single plant in the West Siberian Region and a mixed infection of 16SrIII-B and 16SrI-C was detected in three plants, one in the Northern Region and two in the Central Region. Eleven species of insects of the order Hemiptera, suborder Auchenorrhyncha, were collected from leguminous plants in the Moscow oblast of the Central Region. Euscelis incisus and Aphrodes bicinctus were the most prevalent species and may be potential phytoplasma vectors in the Central Region.

Characterization of Direct Current-Electrical Penetration Graph Waveforms and Correlation With the Probing Behavior of Matsumuratettix hiroglyphicus (Hemiptera: Cicadellidae), the Insect Vector of Sugarcane White Leaf Phytoplasma.

The leafhopper Matsumuratettix hiroglyphicus (Matsumura) (Hemiptera: Cicadellidae) is an important vector of phytoplasma causing white leaf disease in sugarcane. Thus, the aim of our study was to understand and describe the stylet-probing activities of this vector while feeding on sugarcane plants, by using direct current (DC) electrical penetration graph (EPG) monitoring. The EPG signals were classified into six distinct waveforms, according to amplitude, frequency, voltage level, and electrical origin of the observed traces during stylet penetration into the host plant tissues (probing). These six EPG waveforms of probing behavior comprise no stylet penetration (NP); stylet pathway through epidermis, mesophyll, and parenchymal cells (waveform A); contact at the bundle sheath layer (waveform B); salivation into phloem sieve elements (waveform C); phloem sap ingestion (waveform D); and short ingestion time of xylem sap (waveform E). The above waveform patterns were correlated with histological data of salivary sheath termini in plant tissue generated from insect stylet tips. The key findings of this study were that M. hiroglyphicus ingests the phloem sap at a relatively higher rate and for longer duration from any other cell type, suggesting that M. hiroglyphicus is mainly a phloem-feeder. Quantitative comparison of probing behavior revealed that females typically probe more frequently and longer in the phloem than males. Thus, females may acquire and inoculate greater amounts of phytoplasma than males, enhancing the efficiency of phytoplasma transmission and potentially exacerbating disease spreading. Overall, our study provides basic information on the probing behavior and transmission mechanism of M. hiroglyphicus.

Molecular and cellular analysis of immunity in the phytoplasma vector Euscelidius variegatus: exploiting immunity to improve biological control strategies

Insects depend on innate immunity only to defend themselves against pathogens and to regulate interactions with many other microorganisms, such as different kinds of symbionts. Recently, it has been suggested that immunocytes could play a role in the vectorial capacity of insects leading to an increased interest towards primary immunocyte cultures. We analysed at molecular and cellular level the immune response of the leafhopper Euscelidius variegatus with the aim to provide an in vitro model for studying the insect-microbe interactions. We in vitro cultured and kept alive for more than 3 months E. variegatus immunocytes that showed a mitotic capacity as well as adhesion and phagocytic activities. In situ hybridization revealed that the defensin gene is actively transcribed in cultured immunocytes, while cecropins were not recorded in this species. These promising results obtained with E. variegaus, a leafhopper frequently used as a laboratory experimental model of insect vector of phytoplasmas, will help in developing in vitro tools for the study of the interactions between these pathogens and their vectors.

Effect of temperature on the development and reproduction of the sugarcane white leaf insect vector, Matsumuratettix hiroglyphicus (Matsumura) (Hemiptera: Cicadellidae)

The biological and life-history parameters of the leafhopper, Matsumuratettix hiroglyphicus (Matsumura), a vector of sugarcane white leaf phytoplasma, were studied on sugarcane host plants, at different constant temperatures, in the laboratory. The results revealed no complete life cycle development at extreme low and high temperatures of 20°C and 38°C, respectively. There was a significant decrease in adult longevity, and reduced developmental time from egg to adult, with increasing temperatures. Low fecundity and reduced female oviposition period occurred at high temperatures. The sex ratio of male offspring appeared to be higher with increasing temperature (30–35°C), while, at lower temperatures (25–27°C), the ratio of female offspring appeared to be higher. According to the obtained life-history parameters, including intrinsic rate of increase (rm), finite rate of increase (λ), and net reproductive rate (R0) (rm=0.067, λ=10.70days, and R0=21.2), 27°C was the optimum temperature for M. hiroglyphicus development. The lowest temperature developmental threshold and degree-days for leafhopper development from the egg to nymph stages was 11.5°C and 132degree-days, and for development from egg to adult, 12.8°C and 345degree-days. These results provide useful information for predicting M. hiroglyphicus population growth, and thus for evaluation of related insect control programs.

Psyllid Species (Cacopsylla spp.) in Pear Orchards of East Sarajevo

Psyllid species (Cacopsylla spp.) are the most important pests on pear in all regions where this fruit species is grown. Cacopsylla spp. cause direct and indirect damages because they suck the sap and make large amounts of honeydew, which disturbs the normal physiological processes. Some psyllid species vectors of phytoplasma were found (Carraro i sar., 1998). The survey was done in 2011 and 2012 in orchards, in the locations of Vojkovici, Kula, Tilava, Petrovići and Kasindo. In Kula location, survey was done on the following cultivars: Wiliams, General Le Clerc, „Passa Crasana“, Abe Fetel and Poire de Curé. In pear orchards of the East Sarajevo area the following were determined: Cacopsylla pyri Linne, Cacopsylla pyrisuga Foerster and Cacopsylla pyricola Foerster. In intensive orchards of Vojkovići and Kula, C. pyri was more present compared to C. pyrisuga, while in extensive orchards in the location of Kasindo, C. pyrisuga was more present. In semi-intensive orchards, Tilava and Petrovići, the most present was C. pyrisuga, then C. pyri and the least present was C. pyricola. In the locality of Kula, the highest percentage of shoots infeted with C. pyri was the Poire de Curé, and the smallest was of cultivar Abe Fetel.

Elm yellows: A phytoplasma disease of concern in forest and landscape ecosystems

SummaryElm yellows (EY) is a lethal or decline phytoplasma disease that affects several Ulmus (elm) species and hybrids, which is widespread in North America and Europe. The symptoms vary among the elm species. In those native to North America, main symptoms include epinasty, chlorosis, premature casting of the leaves, yellow to brown discoloration of the phloem in the roots and stem and tree death that usually occurs within 1 or 2 years from the appearance of foliar symptoms. In contrast, affected trees of European and Asian species are primarily characterized by witches’ broom as a specific symptom, do not show phloem discoloration and are less prone to decline. The disease is caused by a relatively genetically homogeneous phytoplasma, the EY agent “Candidatus Phytoplasma ulmi,” a member of the EY phytoplasma group or 16SrV group, subgroup 16SrV‐A. In nature, this pathogen exhibits a high plant host specificity. The elm leafhopper Scaphoideus luteolus is the only confirmed vector of EY phytoplasma in North America, whereas Macropsis mendax has been reported as a natural vector in Northern Italy. However, other insect vectors are likely to be involved in its natural spread. Phytoplasmas of other taxonomic groups or 16SrV subgroups, which are known to infect a wide range of plant hosts, have been identified in naturally infected elm trees. However, the pathological relevance of these “non‐elm” phytoplasmas needs to be confirmed in many cases. Their detection is mainly based on the highly sensitive nested PCR assays, while pathological data are lacking. This study summarizes, within the framework of a single comprehensive review, the current knowledge of EY. Gaps in knowledge of this disease and prospects for future research are also critically discussed.

Genome sequence, prevalence and quantification of the first iflavirus identified in a phytoplasma insect vector.

The leafhopper Euscelidius variegatus is a natural vector of chrysanthemum yellows phytoplasma (CY) and an efficient vector of flavescence dorée phytoplasma (FD) under laboratory conditions. During a transcriptome sequencing (RNA-seq) project aimed at investigating the interactions between the insect and the two phytoplasmas, a 10,616-nucleotide-long contig with high sequence similarity to known picorna-like viruses was identified among the assembled insect transcripts. The discovery came totally unexpected, because insects from the laboratory colony did not show any evident symptom that could be related to the presence of a virus. The amino acid sequence, the shape and size of viral particles, and the results of phylogenetic analysis suggest that this virus, named Euscelidius variegatus virus 1 (EVV-1), can be considered a new member of a new species in the genus Iflavirus. EVV-1 was detected in all of the tested insects from the laboratory colony used for RNA-seq, both in phytoplasma-exposed and in non-exposed insects, but the viral load measured in FD-exposed samples was significantly lower than that in non-exposed insects. This result suggests the possible existence of an intriguing cross-talk among insects, endogenous bacteria, and viruses. The identification of two other E. variegatus laboratory colonies that were free of EVV-1 could represent the key to addressing some basic virological issues, e.g., viral replication and transmission mechanisms, and offer the opportunity to use infectious clones to express heterologous genes in the leafhopper and manipulate the expression of endogenous genes by promoting virus-induced gene silencing.

Behavioral responses of Hyalesthes obsoletus to host-plant volatiles cues

The polyphagous planthopper Hyalesthes obsoletus Signoret is considered to be the principal vector of stolbur phytoplasma, which is associated with yellow diseases of grapevine. To explore the possibility of developing novel control strategies, the behavioral responses to six synthetic mixtures and nine single compounds, previously identified from the headspace of Vitex agnus-castus L. (chaste tree) and Urtica dioica L. (nettle), were investigated in Y-tube bioassays. Choice tests revealed differences in the behavioral responses of males and females to the volatiles that they were exposed to. Males were attracted to a mixture containing (E)-β-caryophyllene, 1,8-cineole, (E,E)-α-farnesene, (E)-β-farnesene, and methyl salicylate (mixture 2). The addition of methyl benzoate to this five-compound mixture (mixture 3) did not attract males but elicited positive responses in females. Furthermore, females were attracted to a mixture containing (E)-β-caryophyllene, (E,E)-α-farnesene, (Z)-3-hexenyl acetate, (Z)-3-hexen-1-ol, and benzothiazole (mixture 4), but here addition of methyl salicylate (mixture 5) did not attract females. Neither males nor females showed attractivity or repellency toward the singly tested compounds. This study enhances knowledge on the interaction of insect behaviorally effective constituents in complex plant volatile mixtures. The attractive mixtures of plant volatiles identified suggest the possibility of using them in monitoring and management of H. obsoletus.

Occurrence of Scaphoideus titanus Ball and some other Auchenorrhyncha in the vineyards of western Slovakia

A study of Auchenorrhyncha was carried out in 2014 and 2015 in 7 vineyard plots with different varieties and pest management strategies in the Nitra wine region and Lesser Carpathian wine region in western Slovakia. The aim of this study was to obtain information related to the presence of potential vector insects associated with grapevine yellows phytoplasmas from the Flavescence dorée and Bois noir groups. Insects were collected by sweeping with an entomological net. Thirty species of Auchenorrhyncha were identified as belonging to 6 families. Cicadellidae were the most abundant, comprising 20 species. Scaphoideus titanus was collected at 4 localities. Identification of the phytoplasma vector is critical to the national strategy for assessment and control of vectors spreading the phytoplasma disease in Slovakian vineyards. The first finding of Metcalfa pruinosa was noticed in vineyards in Slovakia.

Determining putative vectors of the Bogia Coconut Syndrome phytoplasma using loop-mediated isothermal amplification of single-insect feeding media.

Phytoplasmas are insect vectored mollicutes responsible for disease in many economically important crops. Determining which insect species are vectors of a given phytoplasma is important for managing disease but is methodologically challenging because disease-free plants need to be exposed to large numbers of insects, often over many months. A relatively new method to detect likely transmission involves molecular testing for phytoplasma DNA in sucrose solution that insects have fed upon. In this study we combined this feeding medium method with a loop-mediated isothermal amplification (LAMP) assay to study 627 insect specimens of 11 Hemiptera taxa sampled from sites in Papua New Guinea affected by Bogia coconut syndrome (BCS). The LAMP assay detected phytoplasma DNA from the feeding solution and head tissue of insects from six taxa belonging to four families: Derbidae, Lophopidae, Flatidae and Ricaniidae. Two other taxa yielded positives only from the heads and the remainder tested negative. These results demonstrate the utility of combining single-insect feeding medium tests with LAMP assays to identify putative vectors that can be the subject of transmission tests and to better understand phytoplasma pathosystems.

Bacterial associates of Hyalesthes obsoletus (Hemiptera: Cixiidae), the insect vector of bois noir disease, with a focus on cultivable bacteria

The planthopper Hyalesthes obsoletus (Hemiptera: Cixiidae) is an important vector of phytoplasma diseases in grapevine. In the current study, the bacterial community compositions of symbionts of this insect were examined. Two dominant bacterial lineages were identified by mass sequencing: the obligate symbiont Candidatus Sulcia, and a facultative symbiont that is closely related to Pectobacterium sp. and to BEV, a cultivable symbiont of another phytoplasma vector, the leafhopper Euscelidius variegatus. In addition, one bacterium was successfully isolated in this study – a member of the family Xanthomonadaceae that is most closely related to the genus Dyella. This Dyella-like bacterium (DLB) was detected by FISH analysis in H. obsoletus guts but not ovaries, and its prevalence in H. obsoletus increased during the fall, suggesting that it was acquired by the host through feeding. We found that DLB inhibits Spiroplasma melliferum, a cultivable relative of phytoplasma, suggesting that it is a potential candidate for biological control against phytoplasma in grapevines.

Transmission of ‘Candidatus Phytoplasma asteris’ (16SrI) by Osbornellus horvathi (Matsumura 1908) co-infected with “Ca. Phytoplasma phoenicium” (16SrIX)

High population levels of Osbornellus horvathi (Matsumura 1908) in Mediterranean natural environments and our previous findings of adults infected by ‘Candidatus Phytoplasma phoenicium’, in Sicily in 2012, highlight the potential role of this species as a phytoplasma vector. In the present work, O. horvathi and other Auchenorrhyncha species were collected using sticky traps between May-October of 2013 in a natural area in Sicily. The insects were analyzed for phytoplasma detection and characterization. Among the 20 Auchenorrhyncha species collected, only O. horvathi was positive for phytoplasmas. Phytoplasma transmission to periwinkle and broad bean plants by field-collected phytoplasma-infected O. horvathi individuals was also carried out. The number and composition of Auchenorrhyncha populations in the area were described together with information on the biology of O. horvathi. ‘Candidatus Phytoplasma asteris’ was successfully transmitted to broad bean and periwinkle by field-collected ‘Ca. P. asteris’ and ‘Ca. P. phoenicium’ double-infected O. horvathi, thus highlighting its vector competence for the former phytoplasma. Further studies are required to assess the ability of O. horvathi to transmit ‘Ca. P. phoenicium’.

Grapevine phytoplasma disease in Georgia

Abstract Results of grapevine yellows disease (GY) studies in 2005–2015 are reported. Based on symptoms and Dienes' staining method the disease was detected in Kartli, Kakheti and Guria regions on Vitis vinifera (L.) Rkatsiteli, Saperavi, Shavkapito, Tavkveri, Aladasturi, Kachichi, Ganjuri, Chardonnay, Vitis labrusca (L.) cultivar Isabella, species hybrid cultivar Noah. The phytoplasmas were also visualized by using electron microscopy. The disease seriously modifies the structure of leaf the grapevine phloem, the chlorophyll content and the functioning of sink–source system. According to anatomical characters the studied cultivars showed a decreasing resistance from Noah, to Aladasturi, Rkatsiteli, Kachichi and Saperavi. In the areas of disease epidemic 12 leafhopper species were identified: Agalmatium grylloides (Fabricius, 1794), Cicadella viridis (Linnaeus, 1758), Dictyophara europaea (Linnaeus, 1767), Empoasca vitis (Gothe, 1875), Erythroneura imeretina Dekanoidze, 1962, Hyalesthes mlokosieviczi Signoret, 1879, Hyalesthes obsoletus Signoret, 1865, Lepironia coleoptrata (Linnaeus, 1758), Pentastiridius leporinus (Linnaeus, 1761), Philaenus spumarius (Linnaeus, 1758), Metcalfa pruinosa (Say, 1830), Ricania japonica (Melichar, 1898), which may be possible vectors of grapevine phytoplasmas in Georgia.

New Efficient Natural Leafhopper Vectors of Sugarcane Grassy Shoot Phytoplasma in India

Sugarcane grassy shoot (SCGS) disease is associated with the presence of 16SrXI group phytoplasmas that are transmitted by leafhoppers; limited studies have been performed in India toward its natural transmission. To determine the insect vectors that transmit the disease in nature, leafhopper species from SCGS-infected fields at Shahjahanpur, Central Uttar Pradesh, India, were collected and analyzed for phytoplasma presence using nested polymerase chain reaction with phytoplasma-specific primers. An ~1.2-kb amplified DNA fragment was detected in nested PCR from the three major leafhopper species, viz. Maiestas portica (Melichar), Exitianus indicus (Ross) and Cofana unimaculata (Signoret), and the symptomatic sugarcane leaves of variety CoS 07250. BLASTn analysis of ~1.2-kb 16S rDNA partial sequences obtained from symptomatic sugarcane plants and these leafhoppers revealed 99–100 % sequence identities among themselves and 99 % identity with other reported strains of ‘Candidatus Phytoplasma oryzae’ (16SrXI group). Phylogenetic analysis of 16S rRNA sequences of SCGS, M. portica, C. unimaculata and E. indicus phytoplasma strains also indicated the closest phylogenetic relationship with those of ‘Ca. P. oryzae’ group. Transmission tests and population sampling study further confirmed that M. portica and C. unimaculata were vectors of the SCGS phytoplasma from diseased to healthy sugarcane plants. The identification of new vectors of SCGS phytoplasma suggested that these leafhopper species may be responsible for secondary spread of SCGS phytoplasma.

A regional-scale survey to define the known and potential vectors of grapevine yellow phytoplasmas in vineyards South of Swiss Alps

The most important Grapevine Yellows (GY) phytoplasma diseases in Europe are Flavescence doree (FD) and Bois noir (BN); they are spread in vineyard by two proven vectors, Scaphoideus titanus Ball and Hyalesthes obsoletus Signoret, respectively. Other potential vectors of GY have been identified, which are thought to play a secondary role. The GY control strategies are not always effective and an in-depth study on the ecological cycle of the pathogens at regional scale would be of paramount importance. This study was carried out in 48 representative sites of wine-growing area South of Swiss Alps, with the aim to identify known and potential vectors and to characterize the FD and BN phytoplasmas isolates. Out of 167 Auchenorrhyncha species recorded, 27 were known or potential vectors of phytoplasmas and five of those tested positive for phytoplasmas. S. titanus was infected by 16SrV-D subgroup phytoplasma and no clear relationship between its population density and disease outbreaks was observed. Orientus ishidae harboured 16SrV-C and 16SrV-D subgroups suggesting its potential role in spreading 16SrV-C phytoplasma isolates from arboreal plants to grapevine and FD-D from grapevine to grapevine. H. obsoletus was infected by BN phytoplasmas, tuf-types a and b, however it was collected with relatively low abundance. Reptalus panzeri and R. cuspidatus tested positive to tuf-type b, but only R. cuspidatus was common and abundant in the investigated vineyards. To define the range of alternative vectors using a detailed approach on regional scale provides background information to get a more clear vision on the spreading of phytoplasmas in the vineyards.

First Findings in the Route of the Maize Bushy Stunt Phytoplasma Within Its Vector Dalbulus maidis (Hemiptera: Cicadellidae).

In the pathosystem of Dalbulus madis (DeLong & Wolcott) (Hemiptera: Cicadellidae), a vector of maize bushy stunt phytoplasma (MBSP), the interactions occurring during the passage, invasion, and multiplication of the phytoplasma inside the vector body have been generalized from other pathosystems, with a poor understanding of the specific interactions. With the aim to understand MBSP movement and potential specific interactions with its vector, D. maidis adults were dissected to obtain the intestine and salivary gland of both infected (acquisition access period=4 d; latent period=23 d) and noninfected individuals. The organs were processed for visualization with transmission electronic microscopy. Images of phytoplasma cells were observed in the alimentary canal, epithelium of the mesenteron, hemocele, and salivary gland of the vector, and were confirmed through observation of similar cells in maize roots with advanced disease symptoms. The study of the MBSP movement within its vector shows novel findings between the synergy of the MBSP phytoplasma and D. maidis.

Plant-mediated interspecific horizontal transmission of an intracellular symbiont in insects.

Intracellular reproductive manipulators, such as Candidatus Cardinium and Wolbachia are vertically transmitted to progeny but rarely show co-speciation with the host. In sap-feeding insects, plant tissues have been proposed as alternative horizontal routes of interspecific transmission, but experimental evidence is limited. Here we report results from experiments that show that Cardinium is horizontally transmitted between different phloem sap-feeding insect species through plants. Quantitative PCR and in situ hybridization experiments indicated that the leafhopper Scaphoideus titanus releases Cardinium from its salivary glands during feeding on both artificial media and grapevine leaves. Successional time-course feeding experiments with S. titanus initially fed sugar solutions or small areas of grapevine leaves followed by feeding by the phytoplasma vector Macrosteles quadripunctulatus or the grapevine feeder Empoasca vitis revealed that the symbionts were transmitted to both species. Explaining interspecific horizontal transmission through plants improves our understanding of how symbionts spread, their lifestyle and the symbiont-host intermixed evolutionary pattern.