Epidemiology and Genetic Diversity of Grapevine Leafroll-Associated Viruses in British Columbia

Grapevine leafroll disease (GLD) is a complex associated with one or more virus species belonging to the family Closteroviridae. The majority of viruses in this complex are vectored by one or more species of mealybugs (Pseudococcidae) and/or scale insects (Coccidae). Grape-growing regions of British Columbia (BC), including Okanagan, Similkameen, and Fraser valleys and Kamloops (BC central interior), Vancouver, and Gulf islands, were surveyed during the 2014 and 2015 growing seasons for the presence of four major grapevine leafroll-associated viruses, including Grapevine leafroll-associated virus 1 (GLRaV-1), GLRaV-2, GLRaV-3, and GLRaV-4. In total, 3,056 composite five-vine samples were collected from 153 Vitis vinifera and three interspecific hybrid vineyard blocks. The results showed GLRaV-3 to be the most widespread, occurring in 16.7% of the composite samples, followed by GLRaV-4 (3.9%), GLRaV-1 (3.8%), and GLRaV-2 (3.0%). Mixed infections of two or more GLRaVs were found in 4.1% of the total samples. The relative incidence of GLRaVs differed among regions and vineyard blocks of a different age. Characterization of partial CO1 region from a total of 241 insect specimens revealed the presence of Pseudococcus maritimus, Parthenolecanium corni, and other Pulvinaria sp. in BC vineyards. Spatial patterns of GLRaV-3 infected grapevines in three vineyard blocks from three different regions in the Okanagan Valley showed variable degrees of increase in disease spread ranging from 0 to 19.4% over three growing seasons. Regional differences in the relative incidence and spread of GLD underline the need for region-based management programs for BC vineyards.

Application of Next Generation Sequencing for Diagnostic Testing of Tree Fruit Viruses and Viroids

Conventional detection of viruses and virus-like diseases of plants is accomplished using a combination of molecular, serological, and biological indexing. These are the primary tools used by plant virologists to monitor and ensure trees are free of known viral pathogens. The biological indexing assay, or bioassay, is considered to be the "gold standard" as it is the only method of the three that can detect new, uncharacterized, or poorly characterized viral disease agents. Unfortunately, this method is also the most labor intensive and can take up to three years to complete. Next generation sequencing (NGS) is a technology with rapidly expanding possibilities including potential applications for the detection of plant viruses. In this study, comparisons are made between tree fruit testing by conventional and NGS methods, to demonstrate the efficacy of NGS. A comparison of 178 infected trees, many infected with several viral pathogens, demonstrated that conventional and NGS were equally capable of detecting known viruses and viroids. Comparable results were obtained for 170 of 178 of the specimens. Of the remaining eight specimens, some discrepancies were observed between viruses detected by the two methods, representing less than 5% of the specimens. NGS was further demonstrated to be equal or superior for the detection of new or poorly characterized viruses when compared with a conventional bioassay. These results validated both the effectiveness of conventional virus testing methods and the use of NGS as an additional or alternative method for plant virus detection.

First observation of edge localized modes mitigation with resonant and nonresonant magnetic perturbations in ASDEX Upgrade

First experiments with nonaxisymmetric magnetic perturbations, toroidal mode number n=2, produced by newly installed in-vessel saddle coils in the ASDEX Upgrade tokamak show significant reduction of plasma energy loss and peak divertor power load associated with type-I edge localized modes (ELMs) in high-confinement mode plasmas. ELM mitigation is observed above an edge density threshold and is obtained both with magnetic perturbations that are resonant and not resonant with the edge safety factor profile. Compared with unperturbed type-I ELMy reference plasmas, plasmas with mitigated ELMs show similar confinement, similar plasma density, and lower tungsten impurity concentration.

First Report of Aster Yellow Phytoplasmas ('Candidatus Phytoplasma asteris') in Canadian Grapevines

In North America, elm yellows, aster yellows (AY), and X-disease phytoplasmas have been detected in American grapevines (1), and recently, Bois noir was detected in Canadian vineyards from British Columbia (BC) and Ontario (ON) (2). Typical symptoms of grapevine yellows (GY) include leaf rolling and chlorosis, uneven or total lack of lignification of canes, flower abortion or berry withering, and stunting. In 2006 and 2007, independent surveys were conducted by the Canadian Food Inspection Agency (CFIA) and Agriculture and Agri-Food Canada (AAFC) to detect phytoplasmas in Canadian vineyards containing different cultivars in BC, ON, Québec (QC), Nova Scotia, New Brunswick, and Prince Edward Island. The CFIA collected and tested 651 fresh leaf samples from recently imported grapevines and older grapevines in the same or neighboring blocks displaying symptoms typical of those associated with disease caused by phytoplasmas. Many vineyards were surveyed only once. AAFC collected and tested 3,485 samples from symptomatic and asymptomatic grapevines from established vineyards in ON, BC, and QC. The same vineyards were sampled in ON and BC both years; QC vineyards were only sampled in 2007. AAFC-collected leaf samples were freeze dried and stored at -20°C before processing. CFIA samples were tested by a modified real-time PCR assay and TaqMan probe targeting the 16S ribosomal RNA gene that detects a wide range of known phytoplasmas (2). Positive samples were confirmed by conventional PCR using the phytoplasma-specific primers P1/P7 (3) and the resulting ~1,800-bp fragment was cloned and sequenced as previously described (2). DNA extracted by AAFC was amplified by nested PCR technology with universal phytoplasma specific primer pairs P1/P6 and R16R2/R16F2 (3) and the resulting 1,200-bp fragment was cloned and sequenced. Two plants, one located in ON in 2006 and the other in BC in 2007, were found to be infected with an AY-like phytoplasma by the CFIA. The phytoplasmas detected in both infected plants had a 99.9% nt sequence identity with AY phytoplasma sequences from GenBank (Accession Nos. AF222063 and AY665676, respectively), with the BC isolate also showing 100% identity to a strain of AY, ash witches'-broom phytoplasma (GenBank Accession No. AY566302). AAFC detected phytoplasma DNA in both years in a total of 17 symptomatic plants and 21 asymptomatic plants from different vine varieties in ON, BC, and QC. Positive samples were found to have a 99.0% nt sequence identity to AY subgroup 16SrI-A (GenBank Accession No. AY180956). Sequences were exchanged for confirmation of phytoplasma identity and were deposited in Genbank under Accession Nos. FJ659844 and FJ824597. Phytoplasma strains were identified for all plants in which phytoplasmas were detected. Results show that AY is present in vineyards in the provinces of ON, BC, and QC. To our knowledge, this is the first report of AY being detected in grapevines in Canada. References: (1) E. Boudon-Padieu. Bull. O I V, 79:299, 2003. (2) M. Rott et al. Plant Dis. 91:1682, 2007. (3) E. Tanne et al. Phytopathology 91:741, 2001.

First Report of Colombian datura virus in Brugmansia in Canada

Colombian datura virus (CDV) was first described in 1968 (3) and has since been reported in Europe (4), Japan (see 4 for additional references), and the United States (1,2). CDV is a member of the family Potyviridae with flexuous, filamentous nucleocapsids that can be transmitted by mechanical inoculation and grafting and is known to be vectored by the common aphid Myzus persicae. In the fall of 2007, five Brugmansia plants of unknown species from a Parks Board Collection in a Lower Mainland nursery, British Columbia, Canada, were found to be displaying symptoms typical of a viral infection: chlorotic flecking and mottling on leaves, leaf shrivel, and vein banding. Symptomatic leaves from these five plants were tested by ELISA (Immuno Strip Test, Agdia, Elkhart, IN) for several common viruses including Impatiens necrotic spot, Tobacco mosaic, Cucumber mosaic, and Tomato spotted wilt viruses and found to be negative for all. However, rub inoculations onto the herbaceous indicators Nicotiana occidentalis and N. benthamiana resulted in severe symptom formation including necrosis, wilting, shriveling, stunted growth, petiole and stem tip collapse, as well as collapse from the base of the plants, and plant death within 2 weeks after inoculation. A leaf dip assay of the original infected Brugmansia sample and infected N. benthamiana tissue revealed flexuous, potyvirus-like particles with the electron microscope (EM). On the basis of the Brugmansia leaf symptoms and the EM results, a possible infection with CDV was suspected. Primers CDV-3 and CDV-NIb5, specific to CDV (4), were used in a reverse transcription (RT)-PCR assay that amplified an approximate 1,600-bp fragment from the original Brugmansia sample and inoculated N. bentamiana and N. occidentalis plants. The amplified portion of the genome is the extreme 3' terminus and includes the 3' noncoding sequence, the viral coat protein gene, and part of the viral replicase gene. Fragments were cloned into pCR2.1-TOPO (Invitrogen, San Diego, CA) and two clones from each plant (total of six clones) were sequenced in both directions. Sequences of all clones were essentially identical, with only three nucleotide differences among the clones (GenBank Accession No. EU571230). BLASTn analysis revealed the highest match to several CDV isolates ranging from 98.7 to 99.5% nucleotide sequence identity. BLASTp analysis of the 451 amino acid viral polyprotein translation product gave a similarly high match with CDV isolates, with the highest match to a Hungarian isolate of CDV (GenBank Accession No. CAD26690) of 99.8% identity, or only one mismatch out of 451 amino acids. An additional group of 15 large symptomless Brugmansia plants, located approximately 6 m from the five symptomatic plants, were also tested by RT-PCR and found to be positive. These 15 plants were of a different but also unknown species of Brugmansia. In conclusion, analysis of symptomatic Brugmansia from a Canadian collection by transfer of disease to herbaceous indicators, EM, RT-PCR, and genomic sequence comparisons, are consistent with the detection and identification of the potyvirus Colombian datura virus. To our knowledge, this is the first report of this viral pathogen in Canada. References: (1) S. Adkins et al. Phytopathology (Abstr.) 95(suppl.):S2, 2005. (2) C. R. Fry et al. J. Phytopathol. 152:200, 2004. (3) R. P. Kahn and R. Bartels. Phytopathology 58:58, 1968. (4) J. Schubert et al. J. Phytopathol. 154:343, 2006.

First Report of Bois Noir Phytoplasma in Grapevine in Canada

During the summer and fall of 2006, a survey was done to detect European phytoplasmas of quarantine significance in Canadian vineyards. This survey was developed as one of the 2006 import requirements for grapevine nursery stock from Europe. This addresses the increased concerns regarding inadvertent phytoplasma introductions. Grapevines imported in 2006 and established grapevines were observed for symptoms typical of those associated with diseases caused by phytoplasmas on grapevine. Samples were tested from 155 grapevines. One plant, located in the lower Okanagan Valley, British Columbia, tested positive by a modified real-time PCR assay and TaqMan probe targeting the 16S region of the ribosomal RNA gene (1), which detects a wide variety of known phytoplasmas. The sample was further analyzed and found to be positive by conventional PCR with the phytoplasma-specific primers, P1/P7 (3), and Stolbur specific primers, STOL11f2/r1 (2). Additional PCR tests with primers specific to flavescence doree (FD9f/r) (2) and western X disease (P1/W INT) (3) were negative. These phytoplasmas are also known to infect grapevine. The approximate 1,800-bp fragment obtained with P1/P7 was sequenced (GenBank Accession No. EU086529) and found to have 99.7% nucleotide sequence identity to the Stolbur STOL #11 isolate (GenBank Accession No. AF248959) originally isolated from eastern Europe. This was the highest match to any available phytoplasma sequence obtained and indicates that the phytoplasma in the British Columbian sample is an isolate of bois noir, a pest of quarantine significance to Canada. Additional phylogenetic analysis using CLUSTAL W (Lasergene; DNASTAR, Madison, WI) confirmed this result. The presence and identity of the phytoplasma was confirmed from a second tissue sample that was analyzed by PCR and sequenced using the same test procedures as for the first sample, with identical results. The bois noir phytoplasma belongs to the stolbur group (16SrVII) with the principal vector being a cixiid planthopper. Stolbur phytoplasmas cause diseases in other crops, but bois noir disease is caused by a specific member of that group and is the only stolbur phytoplasma known to infect grapevines in Europe. The infected grapevine was from a lot of 1,965 plants of Grenache clone 70 on rootstock 3309 clone 143 that was imported from Europe in 2006. All plants in this importation have been destroyed. This phytoplasma has not been detected in any other grapevines in Canada. Additional import conditions requiring hot water treatment of European vines have been implemented for 2007. Further survey work for phytoplasma in grapevine will continue. References: (1) N. M. Christensen et al. Mol. Plant-Microbe Interact. 17:1175, 2004. (2) X. D. Daire et al. Eur. J. Plant Pathol. 103:507, 1997. (3) C. D. Smart et al. Appl. Environ. Microbiol. 62:2988, 1996.

Range of phytoplasma concentrations in various plant hosts as determined by competitive polymerase chain reaction

ABSTRACT For competitive polymerase chain reaction (PCR), an internal standard DNA template was developed that consisted of a highly conserved, internally deleted 16S rDNA fragment of an aster yellows phytoplasma. The internal standard was calibrated using a quantified culture of Acholeplasma laidlawii. Serial dilutions of the internal standard and fixed amounts of target templates from infected plants were coamplified with the same primers, and the products obtained were quantified using an enzyme-linked immunosorbent assay procedure. Analysis of the data revealed that the phytoplasma concentration in the plants examined differed by a factor of about 4 x 10(6). Phytoplasma concentrations of 2.2 x 10(8) to 1.5 x 10(9) cells per g of tissue were identified in periwinkles infected with various phytoplasmas. High to moderate concentrations were detected in Malus domestica (apple) genotypes infected with the apple proliferation phytoplasma, Alnus glutinosa (alder) genotypes infected with the alder yellows phytoplasma, and most aster yellows-infected Populus (poplar) genotypes examined. Very low phytoplasma concentrations, ranging from 370 to 34,000 cells per g of tissue, were identified in proliferation-diseased apple trees on resistant rootstocks 4551 and 4608, yellows-diseased Quercus robur (oak) trees, and Carpinus betulus (hornbeam) trees. Such low concentrations, which corresponded to about 4 to 340 cells in the reaction mixture, could only be detected and quantified by nested PCR.

Growth and form of planetary seedlings: results from a microgravity aggregation experiment

The outcome of the first stage of planetary formation, which is characterized by ballistic agglomeration of preplanetary dust grains due to Brownian motion in the free molecular flow regime of the solar nebula, is still somewhat speculative. We performed a microgravity experiment flown onboard the space shuttle in which we simulated, for the first time, the onset of free preplanetary dust accumulation and revealed the structures and growth rates of the first dust agglomerates in the young solar system. We find that a thermally aggregating swarm of dust particles evolves very rapidly and forms unexpected open-structured agglomerates.

Incidence of classical swine fever (CSF) in wild boar in a densely populated area indicating CSF virus persistence as a mechanism for virus perpetuation

A virological survey was carried out to establish the distribution of classical swine fever (CSF) virus among wild boar in the Federal State of Brandenburg, Germany. Organ materials and blood samples were collected from 11,670 wild boar shot or found dead during the period March 1995 to December 1997. In total 211 (1.8%) wild boar were positive for CSF virus or antigen. The incidence of CSF-positive animals decreased continuously from 4.6% at the beginning of the epidemic in 1995 to 0.7% in 1997. The highest incidence of positive animals (22%) was found in wild-boar piglets younger than 3 months of age in 1995. The findings were indicative for the decisive role which young wild boar play in the epidemiology of CSF. Following intrauterine transfer some of the wild-boar piglets were probably persistently infected with CSF virus as experienced experimentally. Such piglets can be held responsible for CSF virus perpetuation within the wild-boar population. No CSF virus was isolated from adult wild boar weighing more than 75 kg. During 3 years of monitoring a sufficient number of susceptible wild boar, in particular young animals, was available to maintain the infection chain in that area. It was concluded that persistently infected piglets and the high population density of wild boar in the Brandenburg region offered optimal conditions for the establishment of an CSF epidemic.

Hemolytic activity of Trichomonas vaginalis and Tritrichomonas foetus

The hemolytic activity of live isolates and clones of Trichomonas vaginalis and Tritrichomonas foetus was investigated. The isolates were tested against human erythrocytes. No hemolytic activity was detected by the isolates of T. foetus. Whereas the isolates of T. vaginalis lysed erythrocytes from all human blood groups. No hemolysin released by the parasites could be detected. Our preliminary results suggest that hemolysis depend on the susceptibility of red cell membranes to destabilization and the intervention of cell surface receptors as a mechanism of the hemolytic activity. The mechanism could be subject to strain-species-genera specific variation of trichomonads. The hemolytic activity of T. vaginalis is not due to a hemolysin or to a product of its metabolism. Pretreatment of trichomonads with concanavalin A reduced levels of hemolysis by 40%.

Lysis of erythrocytes by Trichomonas gallinae

The hemolytic activity of five live isolates of Trichomonas gallinae was investigated. The isolates were subsequently tested against the erythrocytes of seven adult animal species. Each of the five isolates tested lysed all human blood groups, as well as rabbit, rat, chicken, horse, bovine, and sheep erythrocytes. No hemolysin released by the parasite could be detected. Our preliminary results suggest that the hemolytic activity is not due to the hemolysin release by T. gallinae or to a product of its metabolism. Pretreatment of live trichomonads with concanavalin A reduced levels of hemolysis by 40%.

[Hemolytic activity of various strains and clones of Trichomonas vaginalis and Tritrichomonas suis]

Hemolytic activity of 7 isolates and 2 clones of Trichomonas vaginalis and 1 isolate and 2 clones of Tritrichomonas suis was determined using incubation with erythrocytes. T. vaginalis hemolyzed all human blood groups, and no correlation between pathogenicity and hemolytic activity was observed and no hemolysin released by the parasite could be detected. No hemolytic activity was observed with strains and clones of T. suis against erythrocytes from all blood groups and with swine erythrocytes.