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1
Erb, W. A., J. N. Moore, and R. E. Sterne. "Attraction of Phytophthora cinnamomi Zoospores to Blueberry Roots." HortScience 21, no. 6 (December 1986): 1361–63. http://dx.doi.org/10.21273/hortsci.21.6.1361.
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Abstract The attraction of zoospores of Phytophthora cinnamomi Rands to roots of three cultivars of rabbiteye blueberry (Vaccinium ashei Reade), two species hybrid cultivars of highbush blueberry, and one tetraploid species hybrid selection (US 109) was compared. Zoospores were attracted to the roots of all plants tested. Roots of highbush cultivars ‘Bluetta’ and ‘Patriot’ attracted more zoospores than the rabbiteye cultivars. The number of zoospores attracted to roots of US 109 was greater than the number attracted to the three rabbiteye cultivars, but less than the highbush cultivars. Increased zoospore attraction appeared to be related to root rot susceptibility in blueberries.
2
Kong, Ping. "Carbon Dioxide as a Potential Water Disinfestant for Phytophthora Disease Risk Mitigation." Plant Disease 97, no. 3 (March 2013): 369–72. http://dx.doi.org/10.1094/pdis-09-12-0844-re.
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The spread of Phytophthora spp. through irrigation systems and natural waterways can have a significant impact on plant health and requires mitigation. Pressurized carbon dioxide (CO2) can inactivate Phytophthora nicotianae zoospores but its effectiveness at low pressure and on other species was unknown. This study evaluated the effect of injected CO2 at 63 to 4,000 ppm in irrigation water on zoospore survival of four Phytophthora spp. and infectivity of P. nicotianae zoospores. Zoospore survival of P. nicotianae, P. tropicalis, and P. pini was reduced by over 90% at 4,000 ppm and was reduced by 40% at 125 to 2,000 ppm after a 2-h exposure. Survival of P. megasperma was less affected by injected CO2, with a reduction of 37.1% at ≤4,000 ppm. CO2 treatments at 4,000 ppm for 30 or 120 min of water infested with P. nicotianae at zoospore concentrations of 1,000 and 5,000 ml−1 reduced disease incidence of annual vinca (Catharanthus roseus) by 92 and 75%. Comparable efficacy was observed in the CO2 treatment at 2,000 ppm. The CO2 treatments at <2,000 ppm also significantly reduced disease caused by water infested at 1,000 zoospores ml−1. These results indicate that CO2 may have potential as a safe and effective water disinfestant for Phytophthora spp.
3
Kong, Ping, and Chuanxue Hong. "Zoospore Density-Dependent Behaviors of Phytophthora nicotianae Are Autoregulated by Extracellular Products." Phytopathology® 100, no. 7 (July 2010): 632–37. http://dx.doi.org/10.1094/phyto-100-7-0632.
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Phytophthora species are destructive fungus-like plant pathogens that use asexual single-celled flagellate zoospores for dispersal and plant infection. Many of the zoospore behaviors are density-dependent although the underlying mechanisms are poorly understood. Here, we use P. nicotianae as a model and demonstrate autoregulation of some zoospore behaviors using signal molecules that zoospores release into the environment. Specifically, zoospore aggregation, plant targeting, and infection required or were enhanced by threshold concentrations of these signal molecules. Below the threshold concentration, zoospores did not aggregate and move toward a cauline leaf of Arabidopsis thaliana (Col-0) and failed to individually attack annual vinca (Catharanthus roseus cv. Little Bright Eye). These processes were reversed when supplemented with zoospore-free fluid (ZFF) prepared from a zoospore suspension above threshold densities but not with calcium chloride at a concentration equivalent to extracellular Ca2+ in ZFF. These results suggest that Ca2+ is not a primary signal molecule regulating these communal behaviors. Zoospores coordinated their communal behaviors by releasing, detecting, and responding to signal molecules. This chemical communication mechanism raises the possibility that Phytophthora plant infection may not depend solely on zoospore number in the real world. Single zoospore infection may take place if it is signaled by a common molecule available in the environment which contributes to the destructiveness of these plant pathogens.
4
von Broembsen, Sharon L., and J. W. Deacon. "Calcium Interference with Zoospore Biology and Infectivity of Phytophthora parasitica in Nutrient Irrigation Solutions." Phytopathology® 87, no. 5 (May 1997): 522–28. http://dx.doi.org/10.1094/phyto.1997.87.5.522.
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Calcium, applied as either CaCl2 or Ca(NO3)2 to water or calcium-free soluble fertilizer solution (Peters 20-10-20 Peat Lite Special), affected several important stages of Phytophthora parasitica zoospore behavior relevant to infection and disease spread. Release of zoospores from sporangia was suppressed by Ca2+ concentrations in the range of 10 to 50 meq. These concentrations also curtailed zoospore motility; 20 meq of Ca2+ in fertilizer solution caused all zoospores to encyst within 4 h, whereas 94% of zoospores remained motile in unamended solution. In addition, Ca2+ in the range of 10 to 30 meq stimulated zoospore cysts to germinate in the absence of an organic nutrient trigger, while suppressing the release of a single zoospore (diplanetism) from cysts that did not germinate. In growth chamber experiments, the amendment of the fertilizer solution with 10 or 20 mM Ca(NO3)2 greatly suppressed infection of flood-irrigated, containerized vinca seedlings in a peat-based mix by motile or encysted zoospores of P. parasitica. These results demonstrate that Ca2+ amendments interfere with P. parasitica zoospore biology at multiple stages, with compounding effects on epidemiology, and suggest that manipulation of Ca2+ levels in irrigation water or fertilizer solutions could contribute to management of Phytophthora in recirculating irrigation systems.
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Downer, A. J., J. A. Menge, and E. Pond. "Effects of Cellulytic Enzymes on Phytophthora cinnamomi." Phytopathology® 91, no. 9 (September 2001): 839–46. http://dx.doi.org/10.1094/phyto.2001.91.9.839.
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Two enzyme systems, cellulase (β-1,4-glucanase) and laminarinase (β-1,3-glucanase), were added to soil extracts to simulate (in vitro) lytic components found in mulches suppressive to Phytophthora cinnamomi. Concentration ranges of each enzyme were incubated with Phytophthora cinnamomi mycelium, zoospores, zoospores cysts, and zoospore-infected excised roots to evaluate the roles of each enzyme in potential control of avocado root rot disease. Cellulase significantly retarded the development of zoosporangia and chlamydospores when mycelia were incubated in soil extract containing the enzyme at concentrations greater than 10 units/ml. Zoospore production was also reduced by cellulase but not by laminarinase. Laminarinase had little effect on zoosporangia or chlamydospore formation. At high concentrations, laminarinase was consistently more effective at preventing encystment than cellulase. Chlamydospores preformed in root tips were immune to the lytic effects of all treatments except cellulase at 100 units/ml. Zoospores placed in enzyme solutions and plated on a selective medium survived high cellulase concentrations and formed colonies, but there were fewer surviving zoospores when laminarinase was present at greater than 10 units/ml. Low concentrations of cellulase stimulated infection of excised roots, however, low concentrations of laminarinase prevented infection. Cellulase and laminarinase have different effects on the structures of the Phytophthora cinnamomi life history, however, each enzyme may have a role in reduction of inoculum.
6
Widmer, T. L. "Infective Potential of Sporangia and Zoospores of Phytophthora ramorum." Plant Disease 93, no. 1 (January 2009): 30–35. http://dx.doi.org/10.1094/pdis-93-1-0030.
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Phytophthora species produce sporangia that either germinate directly or release zoospores, depending upon environmental conditions. Previous Phytophthora spp. inoculation trials have used both sporangia and zoospores as the inoculum type. However, it is unknown what impact propagule type has on disease. Rhododendron leaf disks were inoculated with P. ramorum zoospores (75, 500, or 2,400 per disk), sporangia (75 per disk), or sporangia plus trifluoperazine hydrochloride (TFP) (75 per disk), a chemical that inhibits zoospore formation. Combining results from two different isolates, the highest concentration of zoospores (2,400 per disk) induced a significantly higher percentage of necrotic leaf disk area (96.6%) than sporangia (87.6%) and 500 zoospores per disk (88.7%). The sporangia plus TFP treatment had the lowest necrosis at 47.5%. Rooted rhododendron cuttings had a higher percentage of necrotic leaves per plant when inoculated with zoospores (3,000 or 50,000 per ml) or cysts (50,000 per ml) than with sporangia (3,000 per ml) with or without TFP. The percentage of necrotic leaf area was significantly higher when cysts or zoospores were inoculated at 50,000 per ml than sporangia without TFP and zoospores at 3,000 per ml. All treatments were significantly higher in the percentage of necrotic leaf area than the leaves treated with sporangia plus TFP. This demonstrates that the full inoculum potential may not be achieved when sporangia are used as the inoculum propagule.
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Granke, L. L., and M. K. Hausbeck. "Effects of Temperature, Concentration, Age, and Algaecides on Phytophthora capsici Zoospore Infectivity." Plant Disease 94, no. 1 (January 2010): 54–60. http://dx.doi.org/10.1094/pdis-94-1-0054.
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Controlled laboratory studies were undertaken to determine the effects of water temperature (2, 9, 12, 19, 22, and 32°C), inoculum concentration (1 × 102, 1 × 103, 5 × 103, 1 × 104, 2 × 104, and 4 × 104 zoospores/ml), and zoospore suspension age (0, 1, 3, and 5 days old) on infection of pickling cucumbers (Cucumis sativus) by Phytophthora capsici. Zoospore motility and mortality in response to commercial algaecides were also investigated. Cucumbers became infected at all temperatures tested, except 2°C, and the highest infection incidence was observed for cucumbers incubated in suspensions held at ≥19°C. Fewer fruit (<40% at ≥19°C, 0% at ≤12°C) became infected when water contained 1 × 102 zoospores/ml. Almost 100% of fruit were infected when water contained ≥5 × 103 zoospores/ml at temperatures ≥12°C. While the incidence of fruit infection declined with the zoospore suspension age, infection still occurred when 5-day-old suspensions were used. Commercial algaecides inhibited zoospore motility and caused significant zoospore mortality in laboratory assays, and show promise for treatment of infested irrigation water. Avoidance of infested irrigation water throughout the growing season is warranted until effective and economically acceptable water treatments are developed for field use.
8
Liu, Fang, Bao-hua Li, Sen Lian, Xiang-li Dong, Cai-xia Wang, Zhen-fang Zhang, and Wen-xing Liang. "Effects of Temperature and Moisture on the Infection and Development of Apple Fruit Rot Caused by Phytophthora cactorum." Plant Disease 102, no. 9 (September 2018): 1811–19. http://dx.doi.org/10.1094/pdis-07-17-1028-re.
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Phytophthora fruit rot, caused by Phytophthora cactorum, is an important disease of apple in China, often causing more than 50% fruit rot in rainy years. We examined the effects of temperature and moisture on the development of the disease and effects of the variables on zoospore release and germination, infection, and lesion development. In vitro, a temperature range of 5 to 20°C had no significant effects on zoospore release dynamics but did significantly affect the quantities of released zoospores. The largest quantity of zoospores was released at 9.9°C according to a fitted model. Zoosporangia released zoospores within 15 min at the test temperatures (0 to 20°C), which peaked at the fourth hour. Zoospores germinated in vitro, requiring free water, at temperatures from 5 to 35°C. The optimum germination temperature was 25.1°C according to a fitted model. The minimum wetness duration required for zoospores to complete the infection process and induce visible lesions on Fuji fruit was 0.40 h at the optimal temperature of 23.0°C according to the fitted model, whereas observed values were 4.5, 1.5, 0.5, 1.5 and 8.5 h at 10, 15, 20, 25, and 30°C, respectively. The number of zoospore infections on fruit at various temperatures and wetness durations were well fitted by the modified Weibull model; based on the model, the optimal temperature for zoospore infections was 23.0°C. Young apple fruit infected by zoospores developed visible lesions from 10 to 30°C, with a predicted optimum of 23.5°C; no lesions developed at 5 or 35°C. The shortest incubation period of the disease was 4 days. These results can be used to develop disease forecasting models for improved fungicide control.
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Bassani, Ilaria, Corinne Rancurel, Sophie Pagnotta, François Orange, Nicolas Pons, Kevin Lebrigand, Franck Panabières, Laurent Counillon, Xavier Noblin, and Eric Galiana. "Transcriptomic and Ultrastructural Signatures of K+-Induced Aggregation in Phytophthora parasitica Zoospores." Microorganisms 8, no. 7 (July 7, 2020): 1012. http://dx.doi.org/10.3390/microorganisms8071012.
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Most pathogenic oomycetes of the genus Phytophthora spread in water films as flagellated zoospores. Zoospores perceive and produce signals attracting other zoospores, resulting in autoaggregation in vitro or biofilm formation on plant surface. The mechanisms underlying intercellular communication and consequent attraction, adhesion and aggregation are largely unknown. In Phytophthora parasitica, the perception of a K+ gradient induces coordinated motion and aggregation. To define cellular and molecular events associated with oomycete aggregation, we combined transcriptomic and ultrastructural analyses. Results indicate involvement of electroception in K+ sensing. They establish that the transcriptome repertoire required for swimming and aggregation is already fully functional at zoospore release. At the time points analyzed, aggregates are mainly constituted of zoospores. They produce vesicular and fibrillary material discharged at cell-to-cell contacts. Consistently, the signature of transcriptome dynamics during transition to aggregates is an upregulation of genes potentially related to vesicular trafficking. Moreover, transcriptomic and functional analyses show a strong enhancement of carbonic anhydrase activity, indicating that pH homeostasis may contribute to aggregation by acting on both zoospore movement and adhesion. This study poses the molecular and cellular bases of aggregative behavior within oomycetes and expands the current knowledge of ion perception-mediated dissemination of propagules in the rhizosphere.
10
Bishop-Hurley, Sharon L., Sarah A. Mounter, James Laskey, Roy O. Morris, Jim Elder, Philip Roop, Chris Rouse, Francis J. Schmidt, and James T. English. "Phage-Displayed Peptides as Developmental Agonists for Phytophthora capsici Zoospores." Applied and Environmental Microbiology 68, no. 7 (July 2002): 3315–20. http://dx.doi.org/10.1128/aem.68.7.3315-3320.2002.
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ABSTRACT As part of its pathogenic life cycle, Phytophthora capsici disperses to plants through a motile zoospore stage. Molecules on the zoospore surface are involved in reception of environmental signals that direct preinfection behavior. We developed a phage display protocol to identify peptides that bind to the surface molecules of P. capsici zoospores in vitro. The selected phage-displayed peptides contained an abundance of polar amino acids and proline but were otherwise not conserved. About half of the selected phage that were tested concomitantly induced zoospore encystment in the absence of other signaling agents. A display phage was shown to bind to the zoospore but not to the cyst form of P. capsici. Two free peptides corresponding to active phage were similarly able to induce encystment of zoospores, indicating that their ability to serve as signaling ligands did not depend on their exact molecular context. Isolation and subsequent expression of peptides that act on pathogens could allow the identification of receptor molecules on the zoospore surface, in addition to forming the basis for a novel plant disease resistance strategy.
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Galiana, Eric, Celine Cohen, Philippe Thomen, Catherine Etienne, and Xavier Noblin. "Guidance of zoospores by potassium gradient sensing mediates aggregation." Journal of The Royal Society Interface 16, no. 157 (August 2019): 20190367. http://dx.doi.org/10.1098/rsif.2019.0367.
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The biflagellate zoospores of some phytopathogenic Phytophthora species spontaneously aggregate within minutes in suspension. We show here that Phytophthora parasitica zoospores can form aggregates in response to a K + gradient with a particular geometric arrangement. Using time-lapse live imaging in macro- and microfluidic devices, we defined (i) spatio-temporal and concentration-scale changes in the gradient, correlated with (ii) the cell distribution and (iii) the metrics of zoospore motion (velocity, trajectory). In droplets, we found that K + -induced aggregates resulted from a single biphasic temporal sequence involving negative chemotaxis followed by bioconvection over a K + gradient concentration scale [0–17 mM]. Each K + -sensing cell moved into a region in which potassium concentration is below the threshold range of 1–4 mM, resulting in swarming. Once a critical population density had been achieved, the zoospores formed a plume that migrated downward, with fluid advection in its wake and aggregate formation on the support surface. In the microfluidic device, the density of zoospores escaping potassium was similar to that achieved in droplets. We discuss possible sources of K + gradients in the natural environment (zoospore population, microbiota, plant roots, soil particles), and implications for the events preceding inoculum formation on host plants.
12
Hua, Chenlei, Yonglin Wang, Xiaobo Zheng, Daolong Dou, Zhengguang Zhang, Francine Govers, and Yuanchao Wang. "A Phytophthora sojae G-Protein α Subunit Is Involved in Chemotaxis to Soybean Isoflavones." Eukaryotic Cell 7, no. 12 (October 17, 2008): 2133–40. http://dx.doi.org/10.1128/ec.00286-08.
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ABSTRACT For the soybean pathogen Phytophthora sojae, chemotaxis of zoospores to isoflavones is believed to be critical for recognition of the host and for initiating infection. However, the molecular mechanisms underlying this chemotaxis are largely unknown. To investigate the role of G-protein and calcium signaling in chemotaxis, we analyzed the expression of several genes known to be involved in these pathways and selected one that was specifically expressed in sporangia and zoospores but not in mycelium. This gene, named PsGPA1, is a single-copy gene in P. sojae and encodes a G-protein α subunit that shares 96% identity in amino acid sequence with that of Phytophthora infestans. To elucidate the function, expression of PsGPA1 was silenced by introducing antisense constructs into P. sojae. PsGPA1 silencing did not disturb hyphal growth or sporulation but severely affected zoospore behavior, including chemotaxis to the soybean isoflavone daidzein. Zoospore encystment and cyst germination were also altered, resulting in the inability of the PsGPA1-silenced mutants to infect soybean. In addition, the expressions of a calmodulin gene, PsCAM1, and two calcium- and calmodulin-dependent protein kinase genes, PsCMK3 and PsCMK4, were increased in the mutant zoospores, suggesting that PsGPA1 negatively regulates the calcium signaling pathways that are likely involved in zoospore chemotaxis.
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Kuhajek, Jeanne M., Steven N. Jeffers, Marc Slattery, and David E. Wedge. "A Rapid Microbioassay for Discovery of Novel Fungicides for Phytophthora spp." Phytopathology® 93, no. 1 (January 2003): 46–53. http://dx.doi.org/10.1094/phyto.2003.93.1.46.
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A microbioassay was developed for the discovery of compounds that inhibit Phytophthora spp. This assay uses a 96-well format for high-throughput capability and a standardized method for quantitation of initial zoospore concentrations for maximum reproducibility. Zoospore suspensions were quantifiable between 0.7 and 1.5 × 105 zoospores per ml using percent transmittance (620 nm). Subsequent growth of mycelia was monitored by measuring optical density (620 nm) at 24-h intervals for 96 h. Full- and half-strength preparations of each of three media (V8 broth, Roswell Park Memorial Institute mycological broth [RPMI], and mineral salts medium) and four zoospore concentrations (10, 100, 1,000, and 10,000 zoospores per ml) were evaluated. Both full- and half-strength RPMI were identified as suitable synthetic media for growing P. nicotianae, and 1,000 zoospores per ml was established as the optimum initial concentration. The assay was used to determine effective concentration values for 50% growth reduction (EC50) for seven commercial antifungal compounds (azoxystrobin, fosetyl-aluminum, etridiazole, metalaxyl, pentachloronitrobenzene, pimaricin, and propamocarb). These EC50 values were compared with those obtained by measuring linear growth of mycelia on fungicide-amended medium. The microbioassay proved to be a rapid, reproducible, and efficient method for testing the efficacy of compounds that inhibit spore germination in P. nicotianae and should be effective for other species of Phytophthora as well. The assay requires relatively small amounts of a test compound and is suitable for the evaluation of natural product samples.
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Bacic, A., M. L. Williams, and A. E. Clarke. "Studies on the cell surface of zoospores and cysts of the fungus Phytophthora cinnamomi: nature of the surface saccharides as determined by quantitative lectin binding studies." Journal of Histochemistry & Cytochemistry 33, no. 5 (May 1985): 384–88. http://dx.doi.org/10.1177/33.5.3838761.
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The nature of the surface saccharides of zoospores, "partially encysted zoospores" and cysts of the root-rotting fungus Phytophthora cinnamomi, has been examined by quantitative lectin binding studies. Zoospores bound concanavalin A (Con A), but did not bind any of a variety of other lectins tested. In contrast, both cysts and "partially encysted zoospores" bound soybean agglutinin (SBA) as well as Con A. This indicates that accessible alpha-D-glucosyl/alpha-D-mannosyl-containing glycoconjugates predominate at the zoospore surface, whereas both alpha-D-glucosyl/alpha-D-mannosyl and galactosyl and/or N-acetyl-D-galactosaminosyl residues are accessible at the surface of cysts and "partially encysted zoospores." Neither Ulex europeus lectin nor wheat germ agglutinin (WGA) bound to any of the three cell preparations, indicating the absence of accessible alpha-L-fucosyl and N-acetyl-D-glucosaminosyl residues.
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Ridge, G. A., S. N. Jeffers, W. C. Bridges, and S. A. White. "In Situ Production of Zoospores by Five Species of Phytophthora in Aqueous Environments for Use as Inocula." Plant Disease 98, no. 4 (April 2014): 551–58. http://dx.doi.org/10.1094/pdis-06-13-0591-re.
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The goal of this study was to develop a procedure that could be used to evaluate the potential susceptibility of aquatic plants used in constructed wetlands to species of Phytophthora commonly found in nurseries. V8 agar plugs from actively growing cultures of three or four isolates of Phytophthora cinnamomi, P. citrophthora, P. cryptogea, P. nicotianae, and P. palmivora were used to produce inocula. In a laboratory experiment, plugs were placed in plastic cups and covered with 1.5% nonsterile soil extract solution (SES) for 29 days, and zoospore presence and activity in the solution were monitored at 2- or 3-day intervals with a rhododendron leaf disk baiting bioassay. In a greenhouse experiment, plugs of each species of Phytophthora were placed in plastic pots and covered with either SES or Milli-Q water for 13 days during both summer and winter months, and zoospore presence in the solutions were monitored at 3-day intervals with the baiting bioassay and by filtration. Zoospores were present in solutions throughout the 29-day and 13-day experimental periods but consistency of zoospore release varied by species. In the laboratory experiment, colonization of leaf baits decreased over time for some species and often varied among isolates within a species. In the greenhouse experiment, bait colonization decreased over time in both summer and winter, varied among species of Phytophthora in the winter, and was better in Milli-Q water. Zoospore densities in solutions were greater in the summer than in the winter. Decreased zoospore activities for some species of Phytophthora were associated with prolonged temperatures below 13 or above 30°C in the greenhouse. Zoospores from plugs were released consistently in aqueous solutions for at least 13 days. This procedure can be used to provide in situ inocula for the five species of Phytophthora used in this study so that aquatic plant species can be evaluated for potential susceptibility.
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Wang, Yonglin, Aining Li, Xiaoli Wang, Xin Zhang, Wei Zhao, Daolong Dou, Xiaobo Zheng, and Yuanchao Wang. "GPR11, a Putative Seven-Transmembrane G Protein-Coupled Receptor, Controls Zoospore Development and Virulence of Phytophthora sojae." Eukaryotic Cell 9, no. 2 (December 11, 2009): 242–50. http://dx.doi.org/10.1128/ec.00265-09.
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ABSTRACT G protein-coupled receptors (GPCRs) represent a large receptor family involved in a broad spectrum of cell signaling. To understand signaling mechanisms mediated by GPCRs in Phytophthora sojae, we identified and characterized the PsGPR11 gene, which encodes a putative seven-transmembrane GPCR. An expression analysis revealed that PsGPR11 was differentially expressed during asexual development. The highest expression level occurred in zoospores and was upregulated during early infection. PsGPR11-deficienct transformants were obtained by gene silencing strategies. Silenced transformants exhibited no differences in hyphal growth or morphology, sporangium production or size, or mating behavior. However, the release of zoospores from sporangia was severely impaired in the silenced transformants, and about 50% of the sporangia did not completely release their zoospores. Zoospore encystment and germination were also impaired, and zoospores of the transformants lost their pathogenicity to soybean. In addition, no interaction was observed between PsGPR11 and PsGPA1 with a conventional yeast two-hybrid assay, and the transcriptional levels of some genes which were identified as being negatively regulated by PsGPA1 were not clearly altered in PsGPR11-silenced mutants. These results suggest that PsGPR11-mediated signaling controls P. sojae zoospore development and virulence through the pathways independent of G protein.
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Rollins, Lucy, Marianne Elliott, and Gary Chastagner. "Applying Phytophthora ramorum Inoculum to Hosts: A New Method That Simulates Overhead Irrigation." Plant Health Progress 16, no. 2 (January 2015): 100–106. http://dx.doi.org/10.1094/php-rs-15-0008.
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The inoculum threshold for Phytophthora ramorum in irrigation water required for infection of plant material was investigated using a novel pressurized device designed to deliver zoospore inoculum in a way that simulated certain aspects of overhead irrigation. The measured-inoculum spray applicator (MISA) was made from plastic plumbing parts and worked by spraying measured volumes of pressurized zoospore inoculum onto plant material through an adjustable misting nozzle attached to the bottom of the device. Pressurization and spraying of P. ramorum zoospores through the MISA did not significantly affect zoospore viability or infectivity on wounded and non-wounded detached Rhododendron x ‘Nova Zembla’ leaves under controlled laboratory conditions. An inoculum threshold of 51 zoospores/ml was found for infection of Rhododendron leaves by P. ramorum using regression analysis. The MISA can potentially be used to simulate overhead irrigation in research involving pathogenic Phytophthora spp., and the results of the current research may assist nursery managers, property owners, and regulatory agencies in assessing the risk of using P. ramorum infested water for irrigation within nurseries and private landscapes. Accepted for publication 19 June 2015. Published 26 June 2015.
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Zheng, X. B., and W. H. Ko. "Continuing variation in successive asexual generations of Phytophthora cinnamomi following sexual reproduction." Canadian Journal of Botany 74, no. 7 (July 1, 1996): 1181–85. http://dx.doi.org/10.1139/b96-140.
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Colony-type stability of asexual progeny of selfed-oospore cultures of Phytophthora cinnamomi was investigated. Progeny were divided into parental type A, types B to E for those different from type A but with a distinct uniform pattern, and type M for those with the overlapping appearance of two different types. Colonies derived from three successive zoospore generations of isolate P630 were of the same parental A type. However, colonies from oospores of the same isolate consisted of types A, B, C, D, E, and M. Some of the oospore cultures of type A or B and all the type M oospore cultures produced zoospores containing more than one type. Oospore cultures of types C, D, or E that were tested produced zoospores with the same colony type as their respective parent. Among the five cultures randomly selected from asexual progeny produced by oospore isolates P630-21 and P630-6, four displayed continuing variation in colony type in the three to five successive zoospore generations tested. Keywords: asexual variation, continuing variation, Phytophthora cinnamomi, sexual reproduction.
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Chibucos, M. Constantine, and Paul F. Morris. "Levels of Polyamines and Kinetic Characterization of Their Uptake in the Soybean Pathogen Phytophthora sojae." Applied and Environmental Microbiology 72, no. 5 (May 2006): 3350–56. http://dx.doi.org/10.1128/aem.72.5.3350-3356.2006.
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ABSTRACT Polyamines are ubiquitous biologically active aliphatic cations that are at least transiently available in the soil from decaying organic matter. Our objectives in this study were to characterize polyamine uptake kinetics in Phytophthora sojae zoospores and to quantify endogenous polyamines in hyphae, zoospores, and soybean roots. Zoospores contained 10 times more free putrescine than spermidine, while hyphae contained only 4 times as much free putrescine as spermidine. Zoospores contained no conjugated putrescine, but conjugated spermidine was present. Hyphae contained both conjugated putrescine and spermidine at levels comparable to the hyphal free putrescine and spermidine levels. In soybean roots, cadaverine was the most abundant polyamine, but only putrescine efflux was detected. The selective efflux of putrescine suggests that the regulation of polyamine availability is part of the overall plant strategy to influence microbial growth in the rhizosphere. In zoospores, uptake experiments with [1,4-14C]putrescine and [1,4-14C]spermidine confirmed the existence of high-affinity polyamine transport for both polyamines. Putrescine uptake was reduced by high levels of exogenous spermidine, but spermidine uptake was not reduced by exogenous putrescine. These observations suggest that P. sojae zoospores express at least two high-affinity polyamine transporters, one that is spermidine specific and a second that is putrescine specific or putrescine preferential. Disruption of polyamine uptake or metabolism has major effects on a wide range of cellular activities in other organisms and has been proposed as a potential control strategy for Phytophthora. Inhibition of polyamine uptake may be a means of reducing the fitness of the zoospore along with subsequent developmental stages that precede infection.
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Cho, Chung Won, and Melvin S. Fuller. "Ultrastructural organization of freeze-substituted zoospores of Phytophthora palmivora." Canadian Journal of Botany 67, no. 5 (May 1, 1989): 1493–99. http://dx.doi.org/10.1139/b89-198.
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The ultrastructural organization of the zoospores of Phytophthora palmivora was examined using freeze substitution as a potential means of improving upon the images obtained with zoospores preserved by conventional chemical fixation. Despite die technical difficulties encountered, freeze substitution was effective in preserving the overall shape of the zoospores and membranous structures, including the plasma membrane, peripheral cisternae, and the water-expulsion vacuole. Coated pits, not previously reported on the plasma membrane of zoospores of fungi, were found in P. palmivora. The nucleus and cytoskeleton of zoospores were not as well preserved as with conventional chemical fixation. Unique features of freeze-substituted zoospores were compared with structures observed in previous studies of zoospores.
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Rollins, Lucy, Katie Coats, Marianne Elliott, and Gary Chastagner. "Comparison of Five Detection and Quantification Methods for Phytophthora ramorum in Stream and Irrigation Water." Plant Disease 100, no. 6 (June 2016): 1202–11. http://dx.doi.org/10.1094/pdis-11-15-1380-re.
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Propagules of Phytophthora ramorum, the causal agent of sudden oak death (SOD) and ramorum blight, can be recovered from infested stream and nursery irrigation runoff using baiting and filtration methods. Five detection methods, including pear and rhododendron leaf baits, Bottle O’ Bait, filtration, and quantitative polymerase chain reaction (qPCR) performed on zoospores trapped on a filter were compared simultaneously in laboratory assays using lab or creek water spiked with known quantities of P. ramorum zoospores. The detection threshold for each method was determined and methods that could be used to quantify zoospore inoculum were identified. Filtration and qPCR were the most sensitive at detecting low levels of zoospores, followed by wounded rhododendron leaves, rhododendron leaf disks, and pear baits. Filtration, qPCR, and leaf disks were able to quantify P. ramorum zoospores ranging from 2 to 451 direct-plate CFU/liter while wounded leaves and pear baits appeared to be better at detection rather than quantification. The ability to detect and quantify P. ramorum inoculum in water will assist scientists, regulatory agencies, and nursery personnel in assessing the risk of spreading P. ramorum in nurseries and landscape sites where untreated infested water is used for irrigation.
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Taylor, Raymond J., Julie S. Pasche, and Neil C. Gudmestad. "Etiology of a Tuber Rot and Foliar Blight of Potato Caused by Phytophthora nicotianae." Plant Disease 99, no. 4 (April 2015): 474–81. http://dx.doi.org/10.1094/pdis-05-14-0519-re.
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Although Phytophthora nicotianae is not normally considered to be an important pathogen of potato (Solanum tuberosum), intermittent outbreaks of a foliar blight and tuber rot have been reported in the United States over the past 75 years. Due to the sporadic nature of these reports, little is known about the etiology of the disease in potato. However, foliar disease and tuber rots caused by this pathogen are usually centered near areas of standing water in the field and along pivot tracks. Moreover, soil particles adhering to the foliage of infected potato plants suggest that water splash is involved in P. nicotianae dissemination and infection. Soil infestation and water splash dissemination studies were conducted under greenhouse conditions to examine the role that zoospores of P. nicotianae may play in disease on potato. In the soil infestation study, inoculum of P. nicotianae was added to soil at four rates (0.0, 1.0 × 103, 5.0 × 103, and 4.0 × 104 zoospores/ml) and three timings (at planting and 7 and 14 days after planting). Direct infection of aboveground plant tissues was achieved via splash dissemination of inoculum onto potato foliage. All soil infestations significantly reduced emergence, with the exception of the 1.0 × 103 zoospores/ml treatment, and no plants emerged from soil infested with 4.0 ×104 zoospores/ml. Significant reductions in stem number were observed with infestations of 1.0 × 103 and 5.0 × 103 zoospores/ml at planting and 5.0 × 103 zoospores/ml at 7 days after planting. Progeny tuber infections were confirmed with infestations at 1.0 × 103 zoospores/ml at planting and 7 days after planting. Lesions developed on leaflets, petioles, leaf axils, and stems in all water splash dissemination treatments within 3 days of inoculation, significant differences in the lesion number were observed, and disease severity generally was proportional to inoculum concentration. Relative area under the disease progress curve of the 5.0 × 103 and 4.0 × 104 zoospores/ml splash dissemination treatments was significantly greater than the 0.0 zoospore and 1.0 × 103 zoospores/ml treatments. Progeny tuber infections were observed with all water splash dissemination treatments but infection rates did not differ significantly among treatments. These studies confirm the hypothesis that water splash dissemination of P. nicotianae inoculum is a likely means by which infections of this pathogen are initiated in potato.
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Rebollar-Alviter, A., L. V. Madden, S. N. Jeffers, and M. A. Ellis. "Baseline and Differential Sensitivity to Two QoI Fungicides Among Isolates of Phytophthora cactorum That Cause Leather Rot and Crown Rot on Strawberry." Plant Disease 91, no. 12 (December 2007): 1625–37. http://dx.doi.org/10.1094/pdis-91-12-1625.
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Sensitivities of 89 isolates of Phytophthora cactorum, the causal agent of crown rot and leather rot on strawberry plants, from seven states (Florida, Maine, North Carolina, Ohio, Oregon, South Carolina, and New York) to the QoI fungicide azoxystrobin were determined based on mycelium growth and zoospore germination. Radial growth of mycelia on lima bean agar amended with azoxystrobin at 0.001, 0.01, 0.1, 1.0, 10, and 30 μg/ml and salicylhydroxamic acid (SHAM) at 100 μg/ml was measured after 6 days. Effect on zoospore germination was evaluated in aqueous solutions of azoxystrobin at 0.005, 0.01, 0.05, 0.1, 0.5, and 1.0 μg/ml in 96-well microtiter plates by counting germinated and nongerminated zoospores after 4 h at room temperature. SHAM was not used to evaluate zoospore sensitivity. The effective dose to reduce mycelium growth by 50% (ED50) ranged from 0.16 to 12.52 μg/ml for leather rot isolates and 0.10 to 15 μg/ml for crown rot isolates. The Kolmogorov-Smirnov test showed significant differences (P < 0.001) between the two distributions. Zoospores were much more sensitive to azoxystrobin than were mycelia. Differences between sensitivity distributions for zoospores from leather rot and crown rot isolates were significant at P = 0.05. Estimated ED50 values ranged from 0.01 to 0.24 μg/ml with a median of 0.04 μg/ml. Experiments with pyraclostrobin, another QoI fungicide, demonstrated that both mycelia and zoospores of P. cactorum were more sensitive to pyraclostrobin than to azoxystrobin. Sensitivities to azoxystrobin and pyraclostrobin were moderately but significantly correlated (r = 0.60, P = 0.0001).
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Kong, Ping, Gary W. Moorman, John D. Lea-Cox, David S. Ross, Patricia A. Richardson, and Chuanxue Hong. "Zoosporic Tolerance to pH Stress and Its Implications for Phytophthora Species in Aquatic Ecosystems." Applied and Environmental Microbiology 75, no. 13 (May 8, 2009): 4307–14. http://dx.doi.org/10.1128/aem.00119-09.
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ABSTRACT Phytophthora species, a group of destructive plant pathogens, are commonly referred to as water molds, but little is known about their aquatic ecology. Here we show the effect of pH on zoospore survival of seven Phytophthora species commonly isolated from irrigation reservoirs and natural waterways and dissect zoospore survival strategy. Zoospores were incubated in a basal salt liquid medium at pH 3 to 11 for up to 7 days and then plated on a selective medium to determine their survival. The optimal pHs differed among Phytophthora species, with the optimal pH for P. citricola at pH 9, the optimal pH for P. tropicalis at pH 5, and the optimal pH for the five other species, P. citrophthora, P. insolita, P. irrigata, P. megasperma, and P. nicotianae, at pH 7. The greatest number of colonies was recovered from zoospores of all species plated immediately after being exposed to different levels of pH. At pH 5 to 11, the recovery rate decreased sharply (P ≤ 0.0472) after 1-day exposure for five of the seven species. In contrast, no change occurred (P ≥ 0.1125) in the recovery of any species even after a 7-day exposure at pH 3. Overall, P. megasperma and P. citricola survived longer at higher rates in a wider range of pHs than other species did. These results are generally applicable to field conditions as indicated by additional examination of P. citrophthora and P. megasperma in irrigation water at different levels of pH. These results challenge the notion that all Phytophthora species inhabit aquatic environments as water molds and have significant implications in the management of plant diseases resulting from waterborne microbial contamination.
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Barr, D. J. S., and N. L. Désaulniers. "The flagellar apparatus in the Phytophthora infestans zoospore." Canadian Journal of Botany 68, no. 10 (October 1, 1990): 2112–18. http://dx.doi.org/10.1139/b90-276.
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The Phytophthora infestans zoospore contains five out of six rootlets that are found in other secondary-type oomycetous zoospores. They include (i) an anterior ribbed rootlet (AR4) that runs along the right side of the anterior groove and consists of four main microtubules, an electron-opaque cord, and secondary (rib) microtubules; (ii) an anterior rootlet (A2) that runs on the left side of the anterior groove and consists of two microtubules; (iii) a posterior rootlet (P6) that runs on the left side of the posterior groove and consists of six microtubules; (iv) an array of cytoplasmic microtubules; and (v) an array of nucleus-associated microtubules. There is no multistranded, band-shaped rootlet (MS). There is a concertina-like structure in the core of the transition zone distal to the basal plate. Differences in rootlet morphology may provide a useful means of classifying species of Phytophthora. Key words: flagellar apparatus, zoospore, Phytophthora infestans, Oomycetes.
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Sugimoto, T., K. Watanabe, S. Yoshida, M. Aino, K. Irie, T. Matoh, and A. R. Biggs. "Select Calcium Compounds Reduce the Severity of Phytophthora Stem Rot of Soybean." Plant Disease 92, no. 11 (November 2008): 1559–65. http://dx.doi.org/10.1094/pdis-92-11-1559.
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This study investigated the effects of several calcium compounds on Phytophthora stem rot of soybean (Glycine max) and fungal growth and zoospore release of a Phytophthora sojae isolate in vitro. All concentrations of five formulated calcium products [Ca(COOH)2-A, Ca(COOH)2-B, Ca(COOH)2-C, CaSO4-A, and CaCl2-A] and two chemical compounds [CaCl2 and Ca(NO3)2] applied prior to inoculation significantly suppressed disease incidence. Among all the products and chemicals, Ca(COOH)2-A was the most effective in suppressing the incidence of disease. In most cases, no significant relationship was observed between inhibition of growth rate in vitro and disease reduction in growth chamber tests. Therefore, disease suppression recorded in laboratory experiments using pathogen mycelium was likely due to the responses of plant tissues rather than the direct inhibition of pathogen fungal growth by the calcium compounds. The extent of disease reduction was related to increased calcium uptake by plants, suggesting that calcium was the effective element in reducing Phytophthora stem rot. Seedling tray experiments using zoospores indicated that the application of 10 mM Ca(COOH)2-A was more effective for reducing incidence of disease under growth chamber conditions, compared to other concentrations. The presence of 4 to 20 mM of all seven calcium solutions decreased the release of zoospores, although 0.4 mM of all compounds significantly increased zoospore release. Therefore, disease reduction in the growth-chamber experiments was due to the multiple effects of direct suppression on zoospore release and fungal growth in combination with the response of the host plant tissue to Ca(COOH)2-A.
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Judelson, Howard S., and Samuel Roberts. "Novel Protein Kinase Induced during Sporangial Cleavage in the Oomycete Phytophthora infestans." Eukaryotic Cell 1, no. 5 (October 2002): 687–95. http://dx.doi.org/10.1128/ec.1.5.687-695.2002.
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ABSTRACT A study of the effect of inhibitors on zoospore development in Phytophthora infestans demonstrated the involvement of protein kinases and calcium and led to the discovery of a gene induced during zoosporogenesis that encoded a protein resembling Ca+2- and calmodulin-regulated serine/threonine protein kinases. The calcium channel blocker verapamil and the calmodulin antagonist trifluoroperazine inhibited zoosporogenesis and encystment. The protein kinase inhibitors K-252a and KN-93 inhibited zoospore release, encystment, and cyst germination, and K-252a reduced zoospore viability. In contrast, the inhibitors had minor or no effects on sporangia directly germinating in media. Spurred by these findings, a survey of putative protein kinase genes was performed to identify any that were up-regulated during zoosporogenesis. A kinase-encoding gene was identified for which mRNA accumulation was first detected soon after chilling sporangia in water, conditions that induce sporangial cytoplasm to cleave and release zoospores. The transcript persisted in motile zoospores and in germinated cysts but was not detected in other tissues, including hyphae, hyphae placed in water, or directly germinating sporangia. The structure of the predicted protein was novel, as its C-terminal region, which binds calmodulin in related proteins, was unusually short. Concentrations of actinomycin D previously used in experiments that suggested that de novo transcription was not needed for zoosporogenesis or encystment only partially inhibited transcription of the kinase gene, probably due to poor uptake into sporangia.
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Hardham, A. R., and E. Suzaki. "Glycoconjugates on the surface of spores of the pathogenic fungus Phytophthora cinnamomi studied using fluorescence and electron microscopy and flow cytometry." Canadian Journal of Microbiology 36, no. 3 (March 1, 1990): 183–92. http://dx.doi.org/10.1139/m90-032.
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Glycoconjugates on the surface of zoospores and cysts of the pathogenic fungus Phytophthora cinnamomi have been studied using fluorescein isothiocyanate labelled lectins for fluorescence microscopy and flow cytometry, and ferritin- and gold-labelled lectins for ultrastructural analysis. Of the five lectins used, only concanavalin A (ConA) binds to the surface of the zoospores, including the flagella and water expulsion vacuole. This suggests that of accessible saccharides, glucosyl or mannosyl residues predominate on the outer surface of the zoospore plasma membrane. Early in encystment, a system of flat disc-like cisternae, which underlie the zoospore plasma membrane, vesiculate. These and other small peripheral vesicles quickly disappear. After the induction of encystment, ConA is no longer localised close to the plasma membrane but binds to material loosely associated with the cell surface. Quantitative measurements by flow cytometry indicate that the ConA-binding material is gradually lost from the cell surface. The cyst wall is weakly labelled, but the site of germ tube emergence stains intensely. During the first 2 min after the induction of encystment, material that binds soybean agglutinin, Helix pommatia agglutinin, and peanut agglutinin appears on the surface of the fungal cells. The distribution of this material, rich in galactosyl or N-acetyl-D-galactosaminosyl residues, is initially patchy, but by 5 min the material evenly coats most of the cell surface. Labelling of zoospores in which intracellular sites are accessible indicates that the soybean agglutinin binding material is stored in vesicles that lie beneath the plasma membrane. Quantitation of soybean agglutinin labelling shows that maximum binding occurs 2–3 min after the induction of encystment. Key words: cell surface, flow cytometry, lectins, pathogenic fungi, Phytophthora cinnamomi.
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van de Mortel, Judith E., Ha Tran, Francine Govers, and Jos M. Raaijmakers. "Cellular Responses of the Late Blight Pathogen Phytophthora infestans to Cyclic Lipopeptide Surfactants and Their Dependence on G Proteins." Applied and Environmental Microbiology 75, no. 15 (June 5, 2009): 4950–57. http://dx.doi.org/10.1128/aem.00241-09.
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ABSTRACT Oomycete pathogens cause major yield losses for many crop plants, and their control depends heavily on agrochemicals. Cyclic lipopeptides (CLPs) were recently discovered as a new class of natural compounds with strong activities against oomycetes. The CLP massetolide A (Mass A), produced by Pseudomonas fluorescens, has zoosporicidal activity, induces systemic resistance, and reduces late blight in tomato. To gain further insight into the modes of action of CLPs, the effects of Mass A on pore formation, mycelial growth, sporangium formation, and zoospore behavior were investigated, as was the involvement of G proteins in the sensitivity of Phytophthora infestans to Mass A. The results showed that Mass A induced the formation of transmembrane pores with an estimated size of between 1.2 and 1.8 nm. Dose-response experiments revealed that zoospores were the most sensitive to Mass A, followed by mycelium and cysts. Mass A significantly reduced sporangium formation and caused increased branching and swelling of hyphae. At relatively low concentrations, Mass A induced encystment of zoospores. It had no effect on the chemotactic response of zoospores but did adversely affect zoospore autoaggregation. A loss-of-function transformant of P. infestans lacking the G-protein α subunit was more sensitive to Mass A, whereas a gain-of-function transformant required a higher Mass A concentration to interfere with zoospore aggregation. Results indicate that Mass A disturbs various developmental stages in the life cycle of P. infestans and suggest that the cellular responses of P. infestans to this CLP are, in part, dependent on G-protein signaling.
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Muzuni, Muzuni, Haidin Haidin, and Nur Arfa Yanti. "Karakterisasi Morfologi Phytophthora sp. Asal Buah Kakao Desa Olo-oloho, Kabupaten Konawe, Sulawesi Tenggara." BioWallacea : Jurnal Penelitian Biologi (Journal of Biological Research) 7, no. 1 (May 5, 2020): 1064. http://dx.doi.org/10.33772/biowallacea.v7i1.11812.
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This study aimed to determine the morphological characteristics of Phytophthora sp. isolated from cocoa fruits from Olo-oloho Village, Konawe Regency, Southeast Sulawesi. Isolation of Phytophthora sp. carried out by the point method using V4 (Vegetable Juice Agar) media incubated at 27ºC for 24 hours. Morphological characterization of Phytophthora sp. included characterization of colony morphology and cell morphology. The results showed that the colony morphological characteristics were white colonies, cotton-like textures, the uneven edge of the colony, zoning and radial lines. The morphological characteristics of the cell had asexual spores in the form of sporangium and chlamydospores, hyphae are not aseptic, greenish-black zoospores, zoospores are round and double-flagged, and have sporangiophores. Keywords: Phytophthora sp., colony morphology, cell morphology
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Ersek, T., and J. T. English. "Surface-related Changes of Fusing Phytophthora Zoospores." Journal of Phytopathology 146, no. 4 (May 1998): 179–84. http://dx.doi.org/10.1111/j.1439-0434.1998.tb04676.x.
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Škalamera, D., A. P. Wasson, and A. R. Hardham. "Genes expressed in zoospores of Phytophthora nicotianae." Molecular Genetics and Genomics 270, no. 6 (December 3, 2003): 549–57. http://dx.doi.org/10.1007/s00438-003-0946-8.
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Erb, William A., James N. Moore, and Rickie E. Sterne. "Response of Blueberry Cultivars to Inoculation with Phytophthora cinnamomi Rands Zoospores." HortScience 22, no. 2 (April 1987): 298–300. http://dx.doi.org/10.21273/hortsci.22.2.298.
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Abstract Symptom development in resistant and susceptible blueberry cultivars was studied following inoculation with zoospores of Phytophthora cinnamomi Rands. Three rabbiteye (Vaccinium ashei Reade ‘Tifblue’, ‘Woodard’, and ‘Bluegem’), two highbush (V. corymbosum L. ‘Bluetta’ and ‘Patriot’), and one interspecific tetraploid hybrid (US 109) genotypes were grown hydroponically and permitted to develop healthy root systems prior to immersing the roots in a zoospore suspension for 10 hr. P. cinnamomi infected the roots of all cultivars tested. During a 6-week test, root symptom development progressed steadily in ‘Bluetta’ and ‘Patriot’, but leveled off in the other cultivars. ‘Bluetta’ was rated the most susceptible, ‘Patriot’ was intermediate in susceptibility, and US 109, ‘Tifblue’, ‘Woodard’, and ‘Bluegem’ showed increased resistance. The greatest tolerance was exhibited by US 109.
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Gu, Y. H., and W. H. Ko. "Transplantation and subsequent behavior of mitochondria in cells of Phytophthora." Canadian Journal of Microbiology 46, no. 11 (November 1, 2000): 992–97. http://dx.doi.org/10.1139/w00-093.
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Mitochondria isolated from streptomycin-resistant (Sr) protoplasts of Phytophthora parasitica were transferred into chloramphenicol-resistant (Cpr) protoplasts of P. parasitica or Phytophthora capsici with an average successful rate of 1.7 × 10-4, using a selective medium containing streptomycin. No colonies appeared when self-fusion products of donor mitochondria or recipient protoplasts were exposed to the selective medium. Mitochondria isolated from Cpr protoplasts of P. capsici were also transferred into Sr protoplasts of P. parasitica with a similar success rate using a selective medium containing chloramphenicol. Zoospores produced by the Cpr+Sr intraspecific mitochondrial hybrid gave rise to Sr and Cpr+Sr cultures. The second generation zoospores produced by Sr and Cpr+Sr cultures also gave rise to Sr and Cpr+Sr cultures, suggesting the possible occurrence of fusion between some of the Cpr mitochondria and Sr mitochondria, and the displacement of non-fused Cpr mitochondria in the receptor protoplast by the donor Sr mitochondria. Zoospores produced by the interspecific mitochondrial hybrid gave rise to Cpr, Sr, Cpr+Sr, and Cps +Ss cultures. The second generation zoospores produced by Cpr+Sr or Sr cultures also gave rise to the same four types of cultures, suggesting the existence of residual antibiotic-sensitive mitochondria (Cps+Ss) in the parental isolates and the random distribution of Cpr, Sr, and Cps+Ss mitochondria during asexual reproduction. Results suggest that the phenotype of antibiotic resistance / sensitivity was the end result of the interactions among the three types of mitochondria.Key words: mitochondrial transplantation, mitochondrial hybrid, antibiotic resistance, Phytophthora parasitica, Phytophthora capsici.
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Hardham, AR. "Lectin and Antibody Labelling of Surface Components of Spores of Phytophthora cinnamomi." Functional Plant Biology 16, no. 1 (1989): 19. http://dx.doi.org/10.1071/pp9890019.
Full textAbstract:
Molecules on the surface of zoospores and cysts of soilborne fungi such as Phytophthora cinnamomi are important mediators in the early stages of infection of host plants. Surface components of P. cinnamomi cells have been analysed ultrastructurally and at the molecular level using lectins and monoclonal antibodies, with a view to localising and characterising molecules involved in the infection process. Staining with ruthenium red and the lectin, concanavalin A, indicates the presence of a glycocalyx over the surface of the zoospores. Localised antibody binding also reveals that the zoospore surface is subdivided into at least three distinct molecular domains. During encystment, the spectrum of molecules on the cell surface changes dramatically with the secretion of material which is rich in N-acetyl-D-galactosamine and which bonds the cells to any adjacent structure. lmmunolabelling shows that this material is stored in small peripheral vesicles and is secreted 1-3 min after encystment is induced. Encystment can be triggered by the binding of a monoclonal antibody to the flagella, suggesting that specific receptors may be localised there. Surface components on the fungal cells display a variety of taxonomic specificities including those for species and genus. Monoclonal antibodies which bind to these components promise to be valuable tools for diagnostic use.
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Robold, A. V., and A. R. Hardham. "Production of species-specific monoclonal antibodies that react with surface components on zoospores and cysts of Phytophthora nicotianae." Canadian Journal of Microbiology 44, no. 12 (December 1, 1998): 1161–70. http://dx.doi.org/10.1139/w98-120.
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Monoclonal antibodies were generated against components on the surface of zoospores and cysts of the Oomycete, Phytophthora nicotianae, with the aim of obtaining antibodies diagnostic for this species of plant pathogen. A dipstick version of an enzyme-linked immunosorbent assay was used to screen hybridoma cell lines produced by following a coimmunization protocol in which a mouse was immunized with Phytophthora nicotianae cysts mixed with murine antisera raised against cysts of Phytophthora cinnamomi and Phytophthora cryptogea. Of the nine hybridoma cells lines which remained positive, five produced antibodies that reacted with species-specific epitopes on the surface of the spores. Immunofluorescence, immunogold, and immunoblot labelling showed that three of the five species-specific antibodies reacted with a polypeptide of relative molecular mass greater than 205 kDa which was distributed over the entire zoospore surface, including that of the two flagella. These antibodies also labelled the surface of cysts to varying degrees. The other two species-specific antibodies bound to the shaft of tubular mastigonemes that form two rows on the anterior flagellum. In immunoblots, one of these antibodies recognised a 40-kDa glycoprotein. Antibodies produced by the other four hybridoma cell lines reacted with all Phytophthora and Pythium species tested. The results (i) showed that the coimmunization technique effectively produced antibodies directed towards components specific for Phytophthora nicotianae in the presence of antigens common to many Phytophthora species, and (ii) revealed for the first time the biochemical nature of molecular constituents of flagellar mastigonemes in the Oomycetes.Key words: cell surface, flagella, immunodiagnostics, mastigonemes, monoclonal antibodies.
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Ali, Mohammad, Bosung Kim, Kevin D. Belfield, David Norman, Mary Brennan, and Gul Shad Ali. "Inhibition of Phytophthora parasitica and P. capsici by Silver Nanoparticles Synthesized Using Aqueous Extract of Artemisia absinthium." Phytopathology® 105, no. 9 (September 2015): 1183–90. http://dx.doi.org/10.1094/phyto-01-15-0006-r.
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Application of nanoparticles for controlling plant pathogens is a rapidly emerging area in plant disease management, and nanoparticles synthesis methods that are economical and ecofriendly are extensively investigated. In this project, we investigated the potential of silver nanoparticles (AgNPs) synthesized with aqueous extract of Artemisia absinthium against several Phytophthora spp., which cause many economically important crop diseases. In in vitro dose-response tests conducted in microtiter plates, 10 µg ml−1 of AgNPs inhibited mycelial growth of P. parasitica, P. infestans, P. palmivora, P. cinnamomi, P. tropicalis, P. capsici, and P. katsurae. Detailed in vitro dose-response analyses conducted with P. parasitica and P. capsici revealed that AgNPs synthesized with A. absinthium extract were highly potent (IC50: 2.1 to 8.3 µg ml−1) and efficacious (100%) in inhibiting mycelial growth, zoospore germination, germ tube elongation, and zoospore production. Interestingly, AgNP treatment accelerated encystment of zoospores. Consistent with in vitro results, in planta experiments conducted in a greenhouse revealed that AgNP treatments prevented Phytophthora infection and improved plant survival. Moreover, AgNP in in planta experiments did not produce any adverse effects on plant growth. These investigations provide a simple and economical method for controlling Phytophthora with AgNP without affecting normal plant physiology.
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Murray, DIL, DD Darling, and LR Mcgann. "Indirect Effect of Floristic Composition on Production of Sporangia by Phytophthora cinnamomi in Jarrah Forest Soils." Australian Journal of Botany 33, no. 1 (1985): 109. http://dx.doi.org/10.1071/bt9850109.
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Production of sporangia and zoospore discharge by Phytophthora cinnamomi were investigated in jarrah forest soils collected beneath Acacia pulchella, Banksia grandis and Eucalyptus marginata and incubated under conditions which excluded a direct effect of these species on the soil physical environment. Sporangium production was always significantly greater in soils from B. grandis than in soils from A. pulchella; soils from E. marginata gave intermediate results. There was also evidence that discharge of zoospores was suppressed in soils from A. pulchella. Although three isolates of P. cinnamomi differed in their abilities to sporulate per se, they responded similarly to different treatments.
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Savory, Andrew I. M., Laura J. Grenville-Briggs, Stephan Wawra, Pieter van West, and Fordyce A. Davidson. "Auto-aggregation in zoospores of Phytophthora infestans : the cooperative roles of bioconvection and chemotaxis." Journal of The Royal Society Interface 11, no. 94 (May 6, 2014): 20140017. http://dx.doi.org/10.1098/rsif.2014.0017.
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Phytophthora infestans is a highly destructive plant pathogen. It was the cause of the infamous Irish potato famine in the nineteenth century and remains to this day a significant global problem with associated costs estimated at $3 billion annually. Key to the success of this pathogen is the dispersal of free-swimming cells called zoospores. A poorly understood aspect of zoospore behaviour is auto-aggregation —the spontaneous formation of large-scale patterns in cell density. Current competing hypotheses suggest that these patterns are formed by one of two distinct mechanisms: chemotaxis and bioconvection. In this paper, we present mathematical and experimental results that together provide strong evidence that auto-aggregation can only result from a combination of these mechanisms, each having a distinct, time-separated role. A better understanding of the underlying infection mechanisms of P. infestans and potentially other Phytophthora species will in the longer term lead to advances in preventative treatment and thus potentially significant savings in socio-economic costs.
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Latijnhouwers, Maita, Teun Munnik, and Francine Govers. "Phospholipase D in Phytophthora infestans and Its Role in Zoospore Encystment." Molecular Plant-Microbe Interactions® 15, no. 9 (September 2002): 939–46. http://dx.doi.org/10.1094/mpmi.2002.15.9.939.
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We show that differentiation of zoospores of the late blight pathogen Phytophthora infestans into cysts, a process called encystment, was triggered by both phosphatidic acid (PA) and the G-protein activator mastoparan. Mastoparan induced the accumulation of PA, indicating that encystment by mastoparan most likely acts through PA. Likewise, mechanical agitation of zoospores, which often is used to induce synchronized encystment, resulted in increased levels of PA. The levels of diacylglycerolpyrophosphate (DGPP), the phosphorylation product of PA, increased simultaneously. Also in cysts, sporangiospores, and mycelium, mastoparan induced increases in the levels of PA and DGPP. Using an in vivo assay for phospholipase D (PLD) activity, it was shown that the mastoparan-induced increase in PA was due to a stimulation of the activity of this enzyme. Phospholipase C in combination with diacylglycerol (DAG) kinase activity also can generate PA, but activation of these enzymes by mastoparan was not detected under conditions selected to highlight 32P-PA production via DAG kinase. Primary and secondary butanol, which, like mastoparan, have been reported to activate G-proteins, also stimulated PLD activity, whereas the inactive tertiary isomer did not. Similarly, encystment was induced by n- and sec-butanol but not by tert-butanol. Together, these results show that Phytophthora infestans contains a mastoparan- and bu-tanol-inducible PLD pathway and strongly indicate that PLD is involved in zoospore encystment. The role of G-proteins in this process is discussed.
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Dirac, Monica F., John A. Menge, and Monica A. Madore. "Comparison of Seasonal Infection of Citrus Roots by Phytophthora citrophthora and P. nicotianae var. parasitica." Plant Disease 87, no. 5 (May 2003): 493–501. http://dx.doi.org/10.1094/pdis.2003.87.5.493.
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Excised feeder roots from mature citrus trees located in climatically different regions were infected with zoospores of Phytophthora citrophthora and P. nicotianae var. parasitica at different times of the year under identical laboratory conditions. Zoospores encysted on and caused infection in roots from all locations year round. Both pathogens had the most encysted zoospores on roots from November to January and the least from March to May. Infection by P. nicotianae var. parasitica was consistently higher than P. citrophthora in the excised summer roots (May to September) and lower in January 1998 and November 1997. Infection by both species of Phytophthora dropped to a minimum in March when carbohydrate levels in roots were lowest. Temperature was not solely responsible for determining seasonal fluctuations of P. nicotianae var. parasitica and P. citrophthora. Root carbohydrate content also could not be correlated with seasonal infection. Other physiological or microbial factors associated with citrus roots may cause seasonal Phytophthora infection fluctuations. Infection of citrus seedling roots by P. citrophthora at 16°C reduced root starch content but not glucose compared to P. nicotianae var. parasitica, whereas infection at 30°C by P. nicotianae var. parasitica lowered root glucose but not starch content compared to P. citrophthora.
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Érsek, Tibor, James T. English, and James E. Schoelz. "Triparental species hybrids from fused zoospores of Phytophthora." Czech Mycology 50, no. 1 (September 29, 1997): 13–20. http://dx.doi.org/10.33585/cmy.50102.
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Barr, D. J. S., and N. L. Désaulniers. "The flagellar apparatus in zoospores of Phytophthora, Pythium, and Halophytophthora." Canadian Journal of Botany 70, no. 11 (November 1, 1992): 2163–69. http://dx.doi.org/10.1139/b92-267.
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The flagellar apparatuses of 14 species of Phytophthora, 2 of Halophytophthora, and 4 of Pythium are compared in the transmission electron microscope. Except for Phytophthora infestans and Phytophthora mirabilis there were no significant differences in fine structure morphology. There are six flagellar roots: a ribbed triplet consisting of three main microtubules and secondary microtubules; an anterior doublet; a multistranded, band-shaped root of five to nine microtubules; a posterior root of two to four microtubules; and roots consisting of arrays of cytoplasmic microtubules and nuclear-associated microtubules. In P. infestans and P. mirabilis the multistranded root is missing, the posterior root contains five or six microtubules, and the anterior ribbed root contains four main microtubules. The transitional zones in all species are similar. The relationship of the Pythiaceae with other Oomycetes is discussed. Key words: taxonomy, phytogeny, cytology, Oomycetes, Pythiaceae.
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Hu, Jiahuai, Chuanxue Hong, Erik L. Stromberg, and Gary W. Moorman. "Effects of Propamocarb Hydrochloride on Mycelial Growth, Sporulation, and Infection by Phytophthora nicotianae Isolates from Virginia Nurseries." Plant Disease 91, no. 4 (April 2007): 414–20. http://dx.doi.org/10.1094/pdis-91-4-0414.
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Propamocarb hydrochloride is a systemic fungicide commonly used for control of Phytophthora diseases of nursery crops. Here we report on the effect of this compound on different growth stages of Phytophthora nicotianae, a major pathogen of numerous herbaceous and some woody ornamental plants. A total of 71 isolates were assayed for sensitivity to propamocarb at two concentrations of 1.8 mg/ml (label rate) and 10 mg/ml using clarified V8 agar as a base medium. All isolates grew at 10 mg/ml with the most sensitive isolate having 34.8% relative growth compared with growth on nonamended medium. Nine isolates were selected and further tested for mycelial growth at 0, 1, 10, 25, 50, and 100 mg/ml, and for sporangium production, zoospore motility, and germination at 0, 5, 50, 500, 5,000, and 50,000 μg/ml. EC50 values ranged from 2.2 to 90.1 mg/ml for mycelial growth, 133.8 to 481.3 μg/ml for sporangium production, 88.1 to 249.8 μg/ml for zoospore motility, and 1.9 to 184.6 μg/ml for zoospore germination, respectively. In addition, 17 selected isolates were evaluated for propamocarb sensitivity on Pelargonium × hortorum cv. White Orbit. Two days after seedlings were treated with propamocarb at 3.6 mg/ml, they were inoculated by either inverting one 5-mm-diameter plug of a 3-day-old culture or applying a 10-μl drop containing 20 zoospores onto each cotyledon. Propamocarb hydrochloride provided good protection of geranium seedlings from zoospore infections but not from mycelial infections. These results suggest that this fungicide must be used preventively for Phytophthora disease management and that mycelial growth may not be the most reliable measurement to determine the development of fungicide resistance to this compound in Phytophthora species at production facilities and in the landscape.
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Hong, C. X., P. A. Richardson, P. Kong, and E. A. Bush. "Efficacy of Chlorine on Multiple Species of Phytophthora in Recycled Nursery Irrigation Water." Plant Disease 87, no. 10 (October 2003): 1183–89. http://dx.doi.org/10.1094/pdis.2003.87.10.1183.
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Recycled irrigation water is a primary source of inoculum for Phytophthora spp. and is capable of spreading propagules throughout nursery production. Chlorination commonly is used by the industry to disinfest recycled irrigation water; however, chlorine has not been fully researched as a disinfestant for this purpose. In this study, zoospores of seven species and eight isolates of Phytophthora were exposed for 2 min to free available chlorine at 0.25, 0.5, 1.0, 2.0, and 4.0 mg/liter. Zoospores, mycelial fragments, and culture plugs of P. nicotianae also were exposed to chlorine concentrations ranging from 0.25 to 8.0 mg/liter for periods ranging from 15 s to 8 min. In addition, chlorinated water was assayed monthly in 2000 and 2001 at two commercial nurseries, and quarterly in the first year at four other nurseries in Virginia, for chlorine and survival of pythiaceous species using a selective medium. No zoospores of any species tested survived endpoint free chlorine at 2 mg/liter, while limited mycelial fragments of P. nicotianae survived at 8 mg/liter, and mycelial plugs treated at the same level of chlorine were able to produce few sporangia. Phytophthora spp. were recovered only from nursery irrigation water with levels of free chlorine at 0.77 mg/liter or lower. The results of this study are essential for improving current chlorination protocols.
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Gu, Y. H., and W. H. Ko. "Segregation following interspecific transfer of isolated nuclei between Phytophthora parasitica and P. capsici." Canadian Journal of Microbiology 46, no. 5 (May 1, 2000): 410–16. http://dx.doi.org/10.1139/w00-016.
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Nuclei isolated from metalaxyl-resistant (MR) protoplasts of Phytophthora parasitica were transferred into chloroneb-resistant (CnR) protoplasts of Phytophthora capsici and vice versa, with an average success rate of 2.6 × 10-4 (protoplasts with donor nuclei/regenerated protoplasts), using a selective medium containing only the fungicide tolerated by the nuclear donor. No colonies appeared when self-fusion products of donor nuclei or recipient protoplasts were exposed to the selective medium. Colonies produced by the nuclear transfer formed sectors commonly, and differed from the parental types in appearance. All the zoospores produced by the nuclear hybrids were of normal size, and one-fifth of them contained both MR and CnR genes. Since zoospores are mostly uninucleate, these results indicated the occurrence of chromosome re-assortment or mitotic crossing-over following the production of transitory tetraploids, followed by diploidization during zoosporogenesis, thus suggesting the completion of events leading to a parasexual cycle. Hyphal fragment cultures from a nuclear hybrid tested showed considerable variation in growth rate, mycelial morphology, and level of resistance to metalaxyl, indicating uneven distribution and continuous segregation of different types of nuclei in mycelia during vegetative growth.Key words: interspecific nuclear transfer, parasexual cycle, karyogamy, Phytophthora parasitica,Phytophthora capsici.
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Murray, Marion S., and Everett M. Hansen. "Susceptibility of Pacific Yew to Phytophthora lateralis." Plant Disease 81, no. 12 (December 1997): 1400–1404. http://dx.doi.org/10.1094/pdis.1997.81.12.1400.
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In 1991, Pacific yew was reported as a new host for Phytophthora lateralis, an aggressive root pathogen thought previously to be specific to Port Orford cedar. This study was designed to compare the pathogenicity of P. lateralis on the two hosts through seedling, stem, branch, and rootlet inoculations, and field survey. Mortality of inoculated plants averaged 72% for cedar and 4% for Pacific yew, and root colonization by P. lateralis was significantly greater in cedar seedlings than in Pacific yew seedlings. Lesion length on the cedar seedling stems was twice the lesion length on Pacific yew stems, and cedar branches had lesions four times longer than Pacific yew branches. Abundant zoospore aggregation occurred on cedar rootlets along the zone of elongation and the region of maturation. In comparison, far fewer zoospores encysted on Pacific yew rootlets, and they were concentrated on the root hairs. A field survey along 0.8-km stretches of three infested streams in southwest Oregon and northwest California revealed a total of 1,199 dead Port Orford cedar (46% mortality), and 86 dead Pacific yew (10% mortality). We conclude that Pacific yew is less susceptible to P. lateralis than Port Orford cedar.
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Koike, S. T., D. M. Henderson, J. D. MacDonald, and M. S. Ali-Shtayeh. "Phytophthora Root and Crown Rot of Sage Caused by Phytophthora cryptogea in California." Plant Disease 81, no. 8 (August 1997): 959. http://dx.doi.org/10.1094/pdis.1997.81.8.959b.
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In 1996, commercial plantings of sage (Salvia officinalis) in the Salinas Valley in Monterey County, CA, were affected by a root and crown disease. Roots were necrotic, and crowns and lower stems turned black. Affected plants withered and died. A Phytophthora sp. was consistently isolated from roots and stems of the symptomatic plants. The species was identified as Phytophthora cryptogea based upon the formation of hyphal swellings, morphology of sporangia and oospores, and growth at cardinal temperatures (1). Pathogenicity of representative isolates was confirmed by applying 2 ml of a zoospore suspension (2.0 × 105 zoospores per ml) to roots and crowns of 3-month-old potted sage plants. After treatment, plants were placed for 24 h in shallow trays of water to saturate the root zone, then were removed from trays and incubated in a greenhouse. After 4 days, foliage of all inoculated plants began to wilt. After 7 days, plant crowns and stems turned black and the plants collapsed. P. cryptogea was reisolated and recharacterized from all plants. Control plants, which were treated with water and then handled in the same way as inoculated plants, did not develop any symptoms. The tests were repeated and the results were similar. This is the first report of P. cryptogea attacking commercial plantings of sage. The authors also detected this disease in experimental plantings of sage in Stanislaus County in 1990. Reference: (1) D. C. Erwin and O. K. Ribeiro. 1996. Phytophthora Diseases Worldwide. American Phytopathological Society, St. Paul, MN.
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Sanogo, S. "Asexual Reproduction of Phytophthora capsici as Affected by Extracts from Agricultural and Nonagricultural Soils." Phytopathology® 97, no. 7 (July 2007): 873–78. http://dx.doi.org/10.1094/phyto-97-7-0873.
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Formation of sporangia and zoospores in species of Phytophthora is known to be influenced by soil microbial and chemical composition. In Phytophthora capsici, the study of the relationship of soil chemical composition to production of sporangia and zoospores has been limited. P. capsici is a soilborne pathogen of a wide array of vegetable crops, including chile pepper (Capsicum annuum) in New Mexico. Production of sporangia and zoospores by P. capsici was evaluated in extracts of soils from three different environments in New Mexico: (i) agricultural environments with a long history of chile pepper cropping and occurrence of P. capsici (CP), (ii) agricultural environments with no history of chile pepper cropping and no occurrence of P. capsici (Non-CP), and (iii) nonagricultural environments consisting of forests and rangelands (Non-Ag). There was a significant difference in production of P. capsici asexual propagules, expressed as natural log (number of sporangia × number of zoospores), among the three environments (P = 0.0298). Production of propagules was 9 to 13% greater in Non-Ag than in CP or Non-CP environments. Stepwise multiple discriminant analysis and canonical discriminant analysis identified the edaphic variables Na, pH, P, organic matter content, and asexual propagule production as contributing the most to the separation of the three environments. Two significant (P < 0.0001) canonical discriminant functions were derived with the first function, accounting for ≈75% of the explained variance. Based on the two discriminant functions, ≈93, 86, and 89% of observations in CP, Non-CP, and Non-Ag environments, respectively, were classified correctly. Soils from agricultural and nonagricultural environments differentially influence production of sporangia and zoospores in P. capsici, and soil samples could be effectively classified into agricultural and nonagricultural environments based on soil chemical properties and the production of asexual propagules by P. capsici in soil extracts.
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de Souza, Jorge T., Marjan de Boer, Pieter de Waard, Teris A. van Beek, and Jos M. Raaijmakers. "Biochemical, Genetic, and Zoosporicidal Properties of Cyclic Lipopeptide Surfactants Produced by Pseudomonas fluorescens." Applied and Environmental Microbiology 69, no. 12 (December 2003): 7161–72. http://dx.doi.org/10.1128/aem.69.12.7161-7172.2003.
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ABSTRACT Zoospores play an important role in the infection of plant and animal hosts by oomycetes and other zoosporic fungi. In this study, six fluorescent Pseudomonas isolates with zoosporicidal activities were obtained from the wheat rhizosphere. Zoospores of multiple oomycetes, including Pythium species, Albugo candida, and Phytophthora infestans, were rendered immotile within 30 s of exposure to cell suspensions or cell culture supernatants of the six isolates, and subsequent lysis occurred within 60 s. The representative strain SS101, identified as Pseudomonas fluorescens biovar II, reduced the surface tension of water from 73 to 30 mN m−1. The application of cell suspensions of strain SS101 to soil or hyacinth bulbs provided significant protection against root rot caused by Pythium intermedium. Five Tn5 mutants of strain SS101lacked the abilities to reduce the surface tension of water and to cause lysis of zoospores. Genetic characterization of two surfactant-deficient mutants showed that the transposons had integrated into condensation domains of peptide synthetases. A partially purified extract from strain SS101 reduced the surface tension of water to 30 mN m−1 and reached the critical micelle concentration at 25 μg ml−1. Reverse-phase high-performance liquid chromatography yielded eight different fractions, five of which had surface activity and caused lysis of zoospores. Mass spectrometry and nuclear magnetic resonance analyses allowed the identification of the main constituent as a cyclic lipopeptide (1,139 Da) containing nine amino acids and a 10-carbon hydroxy fatty acid. The other four zoosporicidal fractions were closely related to the main constituent, with molecular massesranging from 1,111 to 1,169 Da.