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Prosser, WA, United States

Nelson W.R.,The New Zealand Institute for Plant and Food Research Ltd | Sengoda V.G.,U.S. Department of Agriculture | Alfaro-Fernandez A.O.,Polytechnic University of Valencia | Font M.I.,Polytechnic University of Valencia | And 2 more authors.
European Journal of Plant Pathology | Year: 2013

"Candidatus Liberibacter solanacearum", a phloem-limited and Gram-negative bacterium that is spread from infected to healthy plants by psyllid insect vectors, is an economically important pathogen of solanaceous and carrot crops in the Americas, New Zealand and Europe. Three haplotypes of "Ca. L. solanacearum" have previously been described, two (LsoA and LsoB) in relation to solanaceous crops in the Americas and New Zealand and the third (LsoC) to carrots in Finland. Herein, we describe a fourth haplotype of this 'Candidatus Liberibacter' species (LsoD), also associated with carrots, but from Spain and the Canary Islands and vectored by the psyllid Bactericera trigonica. In addition, LsoC was confirmed in carrot and psyllid samples recently collected from Sweden and Norway. Phylogenetic analysis of the 16S rRNA gene suggests that two of the haplotypes, one in the Americas and the other in northern Europe are closer to each other in spite of a large geographic separation and host differences. Furthermore, during this study, potatoes with symptoms of zebra chip disease recently observed in potato crops in Idaho, Oregon and Washington states were analyzed for haplotype and were found to be positive for LsoA. This liberibacter haplotype was found in psyllids associated with the diseased potato crops as well. This finding contrasts with an earlier report of LsoB from psyllids in Washington which came from a laboratory colony originally collected in Texas. © 2012 US Government. Source


Davies L.J.,Washington State University | Brown C.R.,Vegetable and Forage Crops Research Unit | Elling A.A.,Washington State University
Plant Cell Reports | Year: 2015

Key message: Functional characterization of the Columbia root-knot nematode resistance geneRMc1(blb)in potato revealed theRgene-mediated resistance is dependent on a hypersensitive response and involves calcium.Abstract: The resistance (R) gene RMc1(blb) confers resistance against the plant-parasitic nematode, Meloidogyne chitwoodi. Avirulent and virulent nematodes were used to functionally characterize the RMc1(blb)-mediated resistance mechanism in potato (Solanum tuberosum). Histological observations indicated a hypersensitive response (HR) occurred during avirulent nematode infection. This was confirmed by quantifying reactive oxygen species activity in response to avirulent and virulent M. chitwoodi. To gain an insight into the signal transduction pathways mediating the RMc1(blb)-induced HR, chemical inhibitors were utilized. Inhibiting Ca2+ channels caused a significant reduction in electrolyte leakage, an indicator of cell death. Labeling with a Ca2+-sensitive dye revealed high Ca2+ levels in the root cells surrounding avirulent nematodes. Furthermore, the calcium-dependent protein kinase (CDPK), StCDPK4 had a higher transcript level in RMc1(blb) potato roots infected with avirulent nematodes in comparison to roots infected with virulent M. chitwoodi. The results of this study indicate Ca2+ plays a role in the RMc1(blb)-mediated resistance against M. chitwoodi in potato. © 2014, Springer-Verlag Berlin Heidelberg. Source


Ramesh S.V.,Washington State University | Ramesh S.V.,Directorate of Soybean Research ICAR | Raikhy G.,Washington State University | Brown C.R.,Vegetable and Forage Crops Research Unit | And 2 more authors.
Archives of Virology | Year: 2014

Potato mop-top virus (PMTV; family Virgaviridae) was reported recently in the Pacific Northwestern USA. To better understand the genetic diversity of this virus, the complete genome of an isolate from Washington State (WA), USA, was characterized. Sequence comparisons of the WA isolate with other known sequences revealed that the RNA-Rep-encoded RdRp protein and the RNA-CP-encoded coat protein displayed >99 % amino acid sequence identity to those of two Nordic (RdRp) and several European and North American isolates (CP), respectively. The RNA-TGB-encoded TGB 1 and TGB 3 protein sequences had >99 % amino acid sequence identity to the corresponding proteins of Czech and Danish isolates, whereas the TGB 2 protein is identical to those of Colombian isolates. Phylogenetic analysis of the viral genes of the WA isolate reflected the close relationship between WA and European isolates. RFLP analysis of corresponding DNA of RNA TGB and RNA CP revealed that the WA isolate has the RNA TGB-II and RNA CP-B types, which are prevalent in Europe and other parts of world. This is the first report of the complete genome characterization of PMTV from the Americas. © 2014, Springer-Verlag Wien. Source


Dinh P.T.Y.,Washington State University | Zhang L.,Vegetable and Forage Crops Research Unit | Brown C.R.,Vegetable and Forage Crops Research Unit | Elling A.A.,Washington State University
Journal of Nematology | Year: 2015

Root-knot nematodes (Meloidogyne spp.) are a significant problem in potato (Solanum tuberosum) production. There is no potato cultivar with Meloidogyne resistance, even though resistance genes have been identified in wild potato species and were introgressed into breeding lines. The objectives of this study were to generate stable transgenic potato lines in a cv. Russet Burbank background that carry an RNA interference (RNAi) transgene capable of silencing the 16D10 Meloidogyne effector gene, and test for resistance against some of the most important root-knot nematode species affecting potato, i.e., M. arenaria, M. chitwoodi, M. hapla, M. incognita, and M. javanica. At 35 days after inoculation (DAI), the number of egg masses per plant was significantly reduced by 65% to 97% (P < 0.05) in the RNAi line compared to wild type and empty vector controls. The largest reduction was observed in M. hapla, whereas the smallest reduction occurred in M. javanica. Likewise, the number of eggs per plant was significantly reduced by 66% to 87% in M. arenaria and M. hapla, respectively, compared to wild type and empty vector controls (P < 0.05). Plant-mediated RNAi silencing of the 16D10 effector gene resulted in significant resistance against all of the root-knot nematode species tested, whereas RMc1(blb), the only known Meloidogyne resistance gene in potato, did not have a broad resistance effect. Silencing of 16D10 did not interfere with the attraction of M. incognita second-stage juveniles to roots, nor did it reduce root invasion. © The Society of Nematologists 2015. Source


Davies L.J.,Washington State University | Brown C.R.,Vegetable and Forage Crops Research Unit | Elling A.A.,Washington State University
Plant Cell Reports | Year: 2014

Key message: Functional characterization of the Columbia root-knot nematode resistance geneRMc1(blb)in potato revealed theRgene-mediated resistance is dependent on a hypersensitive response and involves calcium.Abstract: The resistance (R) gene RMc1(blb) confers resistance against the plant-parasitic nematode, Meloidogyne chitwoodi. Avirulent and virulent nematodes were used to functionally characterize the RMc1(blb)-mediated resistance mechanism in potato (Solanum tuberosum). Histological observations indicated a hypersensitive response (HR) occurred during avirulent nematode infection. This was confirmed by quantifying reactive oxygen species activity in response to avirulent and virulent M. chitwoodi. To gain an insight into the signal transduction pathways mediating the RMc1(blb)-induced HR, chemical inhibitors were utilized. Inhibiting Ca2+ channels caused a significant reduction in electrolyte leakage, an indicator of cell death. Labeling with a Ca2+-sensitive dye revealed high Ca2+ levels in the root cells surrounding avirulent nematodes. Furthermore, the calcium-dependent protein kinase (CDPK), StCDPK4 had a higher transcript level in RMc1(blb) potato roots infected with avirulent nematodes in comparison to roots infected with virulent M. chitwoodi. The results of this study indicate Ca2+ plays a role in the RMc1(blb)-mediated resistance against M. chitwoodi in potato. © 2014, Springer-Verlag Berlin Heidelberg. Source

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