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Corvallis, United States

Weiland J.E.,Horticultural Crops Research Laboratory | Weiland J.E.,Oregon State University | Nelson A.H.,Cornell University | Hudler G.W.,Cornell University
Plant Disease | Year: 2010

Phytophthora cactorum, P. citricola I, and P. plurivora cause bleeding cankers on mature European beech (Fagus sylvatica) trees in the northeastern United States. Inoculation experiments were conducted to compare the aggressiveness of the three Phytophthora spp. on stems, leaf disks, and roots of European beech and common lilac (Syringa vulgaris) seedlings. Isolates were obtained from bleeding cankers on European beech from five cities in New York (Albany, Ithaca, Oyster Bay, Plainview, and Rochester) and from a bleeding canker on sugar maple in Ithaca, NY. Stems were inoculated with colonized agar plugs, leaf disks with a zoospore suspension, and roots via infested soil at three inoculum levels. All organs of inoculated beech and lilac developed disease except for lilac roots inoculated with zoospores of P. cactorum. Disease incidence, severity, and plant survival were dependent on isolate and were also influenced by the tissue inoculated and host. Isolates of P. cactorum were the least aggressive and caused less necrosis than isolates of P. citricola I and P. plurivora. Results emphasize the utility of stem and root inoculation for evaluation of this canker disease and underscore critical differences in species aggressiveness.

Seguin J.,University of Basel | Seguin J.,FASTERIS SA | Rajeswaran R.,University of Basel | Malpica-Lopez N.,University of Basel | And 7 more authors.
PLoS ONE | Year: 2014

Virus-infected plants accumulate abundant, 21-24 nucleotide viral siRNAs which are generated by the evolutionary conserved RNA interference (RNAi) machinery that regulates gene expression and defends against invasive nucleic acids. Here we show that, similar to RNA viruses, the entire genome sequences of DNA viruses are densely covered with siRNAs in both sense and antisense orientations. This implies pervasive transcription of both coding and non-coding viral DNA in the nucleus, which generates double-stranded RNA precursors of viral siRNAs. Consistent with our finding and hypothesis, we demonstrate that the complete genomes of DNA viruses from Caulimoviridae and Geminiviridae families can be reconstructed by deep sequencing and de novo assembly of viral siRNAs using bioinformatics tools. Furthermore, we prove that this 'siRNA omics' approach can be used for reliable identification of the consensus master genome and its microvariants in viral quasispecies. Finally, we utilized this approach to reconstruct an emerging DNA virus and two viroids associated with economically-important red blotch disease of grapevine, and to rapidly generate a biologically-active clone representing the wild type master genome of Oilseed rape mosaic virus. Our findings show that deep siRNA sequencing allows for de novo reconstruction of any DNA or RNA virus genome and its microvariants, making it suitable for universal characterization of evolving viral quasispecies as well as for studying the mechanisms of siRNA biogenesis and RNAi-based antiviral defense.

Stewart J.E.,Washington State University | Stewart J.E.,Horticultural Crops Research Laboratory | Andrew M.,Washington State University | Andrew M.,University of Toronto | And 6 more authors.
Mycologia | Year: 2013

SCARs were developed by cloning RAPDPCR amplicons into commercially available vectors, sequencing them and designing specific primers for PCR, direct sequencing and phylogenetic analysis. Eighteen to seventy percent of cloned RAPD-PCR amplicons were phylogenetically informative among closely related small-spored Alternaria spp., Ascochyta spp. and Tilletia spp., taxa that have been resistant to phylogenetic analysis with universally primed, protein-coding sequence data. Selected SCARs were sequenced for larger, population-scale samples of each taxon and demonstrated to be useful for phylogenetic inference. Variation observed in the cloned SCARs generally was higher than variation in nuclear ribosomal internal transcribed spacer (ITS) and several protein-coding sequences commonly used in lower level fungal systematics. Sequence data derived from SCARs will provide sufficient resolution to address lower level phylogenetic hypotheses in Alternaria, Ascochyta, Tilletia and possibly many other fungal groups and organisms. © 2013 by The Mycological Society of America.

Stockwell V.O.,Oregon State University | Johnson K.B.,Oregon State University | Sugar D.,Oregon State University | Loper J.E.,Oregon State University | Loper J.E.,Horticultural Crops Research Laboratory
Phytopathology | Year: 2010

The biological control agents Pseudomonas fluorescens A506 and Pantoea vagans C9-1 were evaluated individually and in combination for the suppression of fire blight of pear or apple in 10 field trials inoculated with the pathogen Erwinia amylovora. The formulation of pathogen inoculum applied to blossoms influenced establishment of the pathogen and the efficacy of biological control. Pantoea vagans C9-1 suppressed fire blight in all five trials in which the pathogen was applied as lyophilized cells but in none of the trials in which the pathogen was applied as freshly harvested cells. In contrast, Pseudomonas fluorescens A506 reduced disease significantly in only one trial. A mixture of the two strains also suppressed fire blight, but the magnitude of disease suppression over all field trials (averaging 32%) was less than that attained by C9-1 alone (42%). The two biological control agents did not antagonize one another on blossom surfaces, and application of the mixture of A506 and C9-1 to blossoms resulted in a greater proportion of flowers having detectable populations of at least one bacterial antagonist than the application of individual strains. Therefore, the mixture of A506 and C9-1 provided less disease control than expected based upon the epiphytic population sizes of the antagonists on blossom surfaces. We speculate that the biocontrol mixture was less effective than anticipated due to incompatibility between the mechanisms by which A506 and C9-1 suppress disease. © 2010 The American Phytopathological Society.

Lee J.C.,Horticultural Crops Research Laboratory
Environmental Entomology | Year: 2010

Methyl salicylate (MeSA) is a common herbivore-induced plant volatile that, when applied to crops, has the potential to enhance natural enemy abundance and pest control. The impacts of MeSA in strawberry were unknown and examined in the spring and midsummer period. Strawberry plots contained no lures (control) or two 30-d MeSA lures (Predalure) in the center: one lure 0.61 m aboveground over a sticky trap, and one lure on a plant near the ground. Arthropod abundance was monitored at the point source, 5 m and 10 m away from lures over 31 d with white sticky traps, pitfall traps, and leaf inspection. Twenty-seven and nine comparisons were made among beneficial and pest arthropods, respectively. Overall positive responses were found among Chrysopidae in JulyAugust 2008 and Orius tristicolor (White) in MayJune 2009 to MeSA based on sticky traps. Chrysopidae showed attraction to the point source, but not at 5 m and 10 m. Ground-dwelling predators collected in pitfall traps such as Araneae, the carabid beetles, Pterostichus melanarius (Illiger), and Nebria brevicollis (Fabricius) did not respond. Increased abundance of six natural enemy groups appeared on various dates between 3 and 24 d after placement of lures in the field based on leaf inspection and sticky traps. Conversely, fewer Coccinellidae were captured on sticky traps on days 03, and fewer natural enemies were observed on leaves on day 28 in MeSA plots. MeSA did not increase nor decrease pest abundance.

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