Sequence analysis of a 1296-nucleotide plasmid from Xylella fastidiosa.

A cryptic plasmid from Xylella fastidiosa strain ATCC 35868 was cloned, sequenced, and the sequence entered into GenBank (U71220). The plasmid is 1296 nucleotides in length with 55% GC content and three open reading frames. A plasmid with sequence homology was found in only one other strain of X. fastidiosa, ATCC 35878. Searches of the GenBank reveal nucleotide sequence homology with plasmid pNKH43 from Stenotrophomonas maltophilia, and amino acid sequence homology with phage Pf3 from Pseudomonas aeruginosa, plasmid pAP12875 from Acetobacter pasteurianus, and plasmid pVT736-1 from Actinobacillus actinomycetemcomitans.

Differential Resistance to Botryosphaeria ribis Among Cercis Taxa.

The redbud (Cercis sp.) is a popular ornamental small tree or shrub, valued commercially for its early spring bloom and adaptability to diverse environmental conditions. Despite these characteristics, large-scale production of redbud has been limited, due in part to their susceptibility to a fungal canker caused by Botryosphaeria ribis. We screened 711 plants in 11 Cercis taxa for response to inoculation with B. ribis. The taxa native to North America, C. canadensis and C. occidentalis, were more susceptible than Asian species. A logistic regression of the number of symptomatic plants 10 weeks postinoculation with taxa and size (stem diameter) as independent variables explained 41% of the variation. Sixteen percent was attributable to taxon effects and 36% was attributable to taxon-independent size effects. Size and taxon effects were not completely orthogonal, and taxa with larger mean stem diameters generally had higher percentages of symptomless plants. A high level of unexplained variation (59%) was found, and is likely due to intraspecific variation among seed lots. Comparisons of 11 seed lots of C. canadensis revealed significantly different proportions of diseased plants ranging from 52 to 92% after 10 weeks, but all plants eventually became diseased.

Permanent Genetic Resources added to the Molecular Ecology Resources Database 1 February 2010-31 March 2010.

This article documents the addition of 228 microsatellite marker loci to the Molecular Ecology Resources Database. Loci were developed for the following species: Anser cygnoides, Apodemus flavicollis, Athene noctua, Cercis canadensis, Glis glis, Gubernatrix cristata, Haliotis tuberculata, Helianthus maximiliani, Laricobius nigrinus, Laricobius rubidus, Neoheligmonella granjoni, Nephrops norvegicus, Oenanthe javanica, Paramuricea clavata, Pyrrhura orcesi and Samanea saman. These loci were cross-tested on the following species: Apodemus sylvaticus, Laricobius laticollis and Laricobius osakensis (a proposed new species currently being described).

Specific PCR detection and identification of Xylella fastidiosa strains causing citrus variegated chlorosis.

By cloning and sequencing specific randomly amplified polymorphic DNA (RAPD) products, we have developed pairs of PCR primers that can be used to detect Xylella fastidiosa in general, and X. fastidiosa that cause citrus variegated chlorosis (CVC) specifically. We also identified a CVC-specific region of the X. fastidiosa genome that contains a 28-nucleotide insertion, and single base changes that distinguish CVC and grape X. fastidiosa strains. When using RAPD products to develop specific PCR primers, we found it most efficient to screen for size differences among RAPD products rather than presence/absence of a specific RAPD band.

Factors affecting somatic embryogenesis in Prunus incisa cv. February Pink.

Factors affecting somatic embryogenesis from root explants of Prunus incisa Thunb. cv. February Pink were investigated. Using a medium containing Murashige and Skoog salts and vitamins supplemented with 10 microM 2,4-dichlorophenoxyacetic (2,4-D), we evaluated the effects of light, growth regulators, amino acids, carbohydrate source, and root induction medium. Explants cultured under light or dark conditions both resulted in the formation of embryos. Embryogenesis was inhibited by the addition of 6-benzyladenine, thidiazuron, or gibberellic acid to the medium. Amino acids were not effective in promoting embryogenesis, with high levels of amino acids actually inhibiting it. Sucrose and glucose effectively induced embryogenesis, while sorbitol and mannitol completely inhibited it. Sucrose and glucose also promoted secondary embryogenesis. Embryos that formed in medium containing 4% or 5% sucrose were abnormally shaped and did not fully develop, while those that formed in medium with sucrose concentrations of 2% or 3% were much more vigorous. Root explants that were induced on medium containing 1.0 micro M indole-3-butyric acid (IBA) produced more somatic embryos than explants induced on medium without IBA. Approximately 50% of the roots induced on medium containing 1.0 microM IBA produced somatic embryos on medium containing 10 microM 2,4-D and 3% sucrose.

Genetic relationships among strains of Xylella fastidiosa from RAPD-PCR data.

Genetic relationships among 11 Xylella fastidiosa strains isolated from mulberry, almond, ragweed, grape, plum, elm, and citrus were determined by random amplified polymorphic DNA (RAPD). Twenty-two 10-base primers amplified a total of 77 discrete polymorphic bands. Phenetic analysis based on a similarity matrix corresponded well with previous reports on X. fastidiosa RFLP-based similarity relationships, indicating that RAPD-PCR amplification products can be used as a reliable indicator of genetic distance in X. fastidiosa. Cladistic analysis suggests the existence of five groups of X. fastidiosa: the citrus group, the plum-elm group, the grape-ragweed group, the almond group, and the mulberry group.

Genetic relationships among strains of Xanthomonas fragariae based on random amplified polymorphic DNA PCR, repetitive extragenic palindromic PCR, and enterobacterial repetitive intergenic consensus PCR data and generation of multiplexed PCR primers useful for the identification of this phytopathogen.

Genetic relationships among 25 isolates of Xanthomonas fragariae from diverse geographic regions were determined by three PCR methods that rely on different amplification priming strategies: random amplified polymorphic DNA (RAPD) PCR, repetitive extragenic palindromic (REP) PCR, and enterobacterial repetitive intergenic consensus (ERIC) PCR. The results of these assays are mutually consistent and indicate that pathogenic strains are very closely related to each other. RAPD, ERIC, and REP PCR assays identified nine, four, and two genotypes, respectively, within X. fragariae isolates. A single nonpathogenic isolate of X. fragariae was not distinguishable by these methods. The results of the PCR assays were also fully confirmed by physiological tests. There was no correlation between DNA amplification product patterns and geographic sites of isolation, suggesting that this bacterium has spread largely through exchange of infected plant germ plasm. Sequences identified through the RAPD assays were used to develop three primer pairs for standard PCR assays to identify X. fragariae. In addition, we developed a stringent multiplexed PCR assay to identify X. fragariae by simultaneously using the three independently derived sets of primers specific for pathogenic strains of the bacteria.

Detection of Xylella fastidiosa in potential insect vectors by immunomagnetic separation and nested polymerase chain reaction.

A sensitive and specific assay for detecting Xylella fastidiosa in potential insect vectors was developed. This assay involves immunomagnetic separation of the bacteria from the insect, followed by a two-step, nested polymerase chain reaction (PCR) amplification using previously developed oligonucleotide primers specific to X. fastidiosa. A total of 347 leafhoppers representing 16 species were captured and sampled from American elm (Ulmus americana L.) trees growing in a nursery where bacterial leaf scorch caused by X. fastidiosa occurs. Two of these leafhopper species, Graphocephala coccinea and G. versuta, regularly tested positive for X. fastidiosa using this technique. These insects are therefore potential vectors of X. fastidiosa. Using immunocapture and nested PCR, it was possible to detect as few as five bacteria per sample.