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E M Hansen - One of the best experts on this subject based on the ideXlab platform.
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phytophthora species causing tanoak Stem Cankers in southwestern oregon
Plant Disease, 2008Co-Authors: Paul Reeser, Wendy Sutton, E M HansenAbstract:Tanoak (Lithocarpus densiflorus) is a principal host of Phytophthora ramorum, cause of sudden oak death (SOD), in the western United States (1). In the course of SOD surveys in southwestern Oregon, other Phytophthora species were encountered to be causing Stem Cankers on tanoak that were indistinguishable from those caused by P. ramorum. In Oregon, SOD is subject to quarantine and eradication. Aerial surveys are flown two or more times a year to locate symptomatic tanoaks, which are then examined from the ground to determine the cause of death. Isolations on selective media were attempted from all trees with Stem Cankers typical of Phytophthora. Phytophthora species were identified by morphological features and DNA sequencing of either internal transcribed spacer (ITS) or the mitochondrial COX spacer region. ITS sequences were compared with validated GenBank records, and COX spacer sequences were compared with known reference isolates in the OSU collection. From 2001 through 2006, Phytophthora spp. were i...
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phytophthora species associated with Stem Cankers on tanoak in southwestern oregon
In: Frankel Susan J.; Kliejunas John T.; Palmieri Katharine M. tech. coords. 2008. Proceedings of the sudden oak death third science symposium. Gen. T, 2008Co-Authors: Paul Reeser, Wendy Sutton, E M HansenAbstract:In effort to eradicate Phytophthora ramorum from Oregon forests, tanoak over its entire range in southwestern Oregon is surveyed intensively for Stem disease. Pieces of bark from the leading edge of tanoak Stem Cankers were plated on cornmeal agar amended with 10 ppm natamycin, 200 ppm a-ampicillin, and 10 ppm rifamycin SV (CARP) to favor the isolation of Phytophthora. Phytophthora ramorum was usually identified on the isolation plates based on the presence of characteristic hyphae, chlamydospores, and sporangia. Hyphae from the leading edge of other colonies resembling Phytophthora were isolated into pure culture. Isolates were grown out to obtain morphological features and DNA extracts for identification. Selected isolates were tested for pathogenicity by inoculating Stems of tanoak seedlings. Phytophthora species isolated from tanoak Stem Cankers include the following: P. cambivora, P. cinnamomi, P. species ?Pg chlamydo,? P. gonapodyides, P. nemorosa, and the proposed new species P. siskiyouensis. An additional isolate may represent a new species of Phytophthora that has not yet been described.
Bruce D.l. Fitt - One of the best experts on this subject based on the ideXlab platform.
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Effects of a penthiopyrad and picoxystrobin fungicide mixture on phoma Stem canker (Leptosphaeria spp.) on UK winter oilseed rape
European Journal of Plant Pathology, 2016Co-Authors: Thomas R. Sewell, Yongju Huang, Steven Moloney, Mike Ashworth, Faye Ritchie, Alla Mashanova, Henrik U. Stotz, Bruce D.l. FittAbstract:In the UK, fungicides are often used to control phoma Stem canker on winter oilseed rape. Field trials were established near Boxworth, Cambridgeshire for four cropping seasons (2011/2012, 2012/2013, 2013/2014 and 2014/15) to test the efficacy of a new fungicide mixture Refinzar® (penthiopyrad + picoxystrobin) by comparison to an existing fungicide Proline 275® (prothioconazole) against phoma Stem canker (Leptosphaeria spp.) and the effect on winter oilseed rape (cv. Catana) yield. In each season, weather data were collected from a weather station at Boxworth and the release of ascospores was monitored using a nearby Burkard spore sampler. The patterns of ascospore release differed between seasons and related to weather conditions. Fungicides penthiopyrad + picoxystrobin and prothioconazole were applied in October/November when 10 % of plants had phoma leaf spotting (T1, early), 4/8 weeks after T1 (T2, late) or at both T1 and T2 (combined). When phoma leaf spot symptoms were assessed in autumn/winter, penthiopyrad + picoxystrobin and prothioconazole both decreased numbers of phoma leaf spots caused by L. maculans; there were few leaf spots caused by L. biglobosa. Penthiopyrad + picoxystrobin and prothioconazole both reduced phoma Stem canker severity before harvest compared to the untreated control but did not increase yield in these seasons when epidemics were not severe. In 2013/2014, the presence of L. maculans and L. biglobosa in upper Stem lesions or Stem base Cankers was determined by species-specific PCR. The proportions of Stems with L. maculans DNA were much greater than those with L. biglobosa DNA for both upper Stem lesions and basal Stem Cankers. These results suggest that both penthiopyrad + picoxystrobin and prothioconazole can decrease phoma Stem canker severity on winter oilseed rape in severe disease seasons.
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Geographic variation in severity of phoma Stem canker and Leptosphaeria maculans/ L. biglobosa populations on UK winter oilseed rape (Brassica napus)
European Journal of Plant Pathology, 2009Co-Authors: J. F. Stonard, Akinwunmi O. Latunde-dada, Yongju Huang, Jonathan West, Neal Evans, Bruce D.l. FittAbstract:Phoma Stem canker, caused by Leptosphaeria maculans and L. biglobosa, is the most important disease of oilseed rape in Europe. Differences between L. maculans and L. biglobosa in their life-cycles enable the two species to co-exist on oilseed rape crops over a cropping season. This review considers the factors affecting geographic variation in the severity of phoma Stem canker epidemics and in the structure of the population of the pathogens in the UK, where the most severe epidemics occur in the south of England and Cankers do not develop in Scotland. It is concluded that this variation is directly related to differences in climate, since weather-based models show that Stem canker severity increases with increasing winter/spring temperature and temperatures are greater in the south of the UK. It may also be related to differences in pathogen populations, since surveys showed that the proportion of the more damaging L. maculans in Stem Cankers was greatest in southern England, with most L. biglobosa in northern England. Regional variation in agronomic practices such as cultivar choice and fungicide use may also indirectly influence phoma Stem canker severity. Differences in cultivar choice result in differences in L. maculans race structure, which may influence the severity of epidemics. Differences in fungicide use may also influence pathogen populations, since L. maculans and L. biglobosa differ in their sensitivities to different azole fungicides. These factors are discussed in relation to strategies for sustainable production of oilseed rape by adaptation to threats posed by climate change.
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Epidemiology and management of Leptosphaeria maculans (phoma Stem canker) on oilseed rape in Australia, Canada and Europe
Plant Pathology, 2001Co-Authors: Jon S. West, P. D. Kharbanda, Martin J. Barbetti, Bruce D.l. FittAbstract:Phoma Stem canker (blackleg), caused by Leptosphaeria maculans, is an important disease on oilseed rape (canola, rapeseed, Brassica napus, Brassica juncea, Brassica rapa) causing seedling death, lodging or early senescence in Australia, Canada and Europe, but not in China. The two forms of L. maculans (A group and B group) that occur on oilseed rape are now considered to be separate species. The epidemiology and severity of phoma Stem canker differs between continents due to differences in the pathogen population structure, oilseed rape species and cultivars grown, climate and agricultural practices. Epidemics are most severe in Australia, where only the A group occurs, and can be damaging in Canada and western Europe, where both A and B groups occur, although their proportions vary within regions and throughout the year. Epidemics are slight in China, where the A group has not been found. Dry climates (Australia, western Canada) lengthen the persistence of infected debris and may synchronize the release of airborne ascospores (after rain) with seedling emergence. L. maculans spreads from cotyledon and leaf infections down petioles to reach the Stem, with infections on cotyledons and leaves early in the season producing the most damaging Stem Cankers at the Stem base (crown). Development of both crown Cankers and phoma Stem lesions higher up Stems is most rapid in regions with high temperatures from flowering to harvest, such as Australia and Canada. Breeding for resistance (genetic, disease escape or tolerance), stubble management, crop rotation and fungicide seed treatments are important strategies for control of phoma Stem canker in all areas. Fungicide spray treatments are justified only in regions such as western Europe where high yields are obtained, and accurate forecasts of epidemic severity are needed to optimize their use.
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Epidemiology of Leptosphaeria maculans in relation to forecasting Stem canker severity on winter oilseed rape in the UK
Annals of Applied Biology, 1999Co-Authors: Jon S. West, Bruce D.l. Fitt, J.e. Biddulph, Peter GladdersAbstract:SUMMARY In the UK, ascospores of Leptosphaeria maculans first infect leaves of oilseed rape in the autumn to cause phoma leaf spots, from which the fungus can grow to cause Stem Cankers in the spring. Yield losses due to early senescence and lodging result if the Stem Cankers become severe before harvest. The risk of severe Stem canker epidemics needs to be forecast in the autumn when the pathogen is still in the leaves, since early infections cause the greatest yield losses and fungicides have limited curative activity. Currently, the most effective way to forecast severe Stem canker is to monitor the onset of phoma leaf spotting in winter oilseed rape crops, although this does not allow much time in which to apply a fungicide. Early warnings of risks of severe Stem canker epidemics could be provided at the beginning of the season through regional forecasts based on disease survey and weather data, with options for input of crop-specific information and for updating forecasts during the winter. The accuracy of such forecasts could be improved by including factors relating to the maturation of ascospores in pseudothecia, the release of ascospores and the occurrence of infection conditions, as they affect the onset, intensity and duration of the phoma leaf spotting phase. Accurate forecasting of severe Stem canker epidemics can improve disease control and optimise fungicide use.
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Differentiating A and B groups of Leptosphaeria maculans, causal agent of Stem canker (blackleg) of oilseed rape
Plant Pathology, 1999Co-Authors: R. H. Williams, Bruce D.l. FittAbstract:Stem canker or blackleg of brassicas, caused by Leptosphaeria maculans, is one of the most damaging diseases of winter oilseed rape in the UK. Airborne ascospores, released in autumn and winter, initiate leaf infections which may lead to colonization of the petiole and, later in the season, formation of Stem lesions and Cankers. Although isolates of the pathogen differ in ability to cause damaging Stem Cankers, this is not readily apparent from leaf spotting or Stem lesion symptoms. However, several cultural, biochemical and genetic characteristics appear to be associated with the ability to form damaging Stem Cankers and isolates can be assigned to one of two groups, termed A and B, on the basis of differences in these characteristics. To investigate the relationship between leaf spotting symptoms and subsequent Stem canker formation, and to improve understanding of the epidemiology of this pathogen, it is desirable to differentiate between the Stem canker forming A group and the less damaging B group of L. maculans. Characterization of isolate type is also important in seed testing and crop breeding programs, particularly in countries such as Canada and Poland where the A type is not ubiquitous. This article reviews methods, including plant assays, assessments of growth characteristics in vitro, isozyme analyses, secondary metabolite profiling, serology, and nucleic acid analyses, that can be used to differentiate the A and B groups.
Paul Reeser - One of the best experts on this subject based on the ideXlab platform.
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Phytophthora nemorosa, a new species causing Cankers and leaf blight of forest trees in California and Oregon, U.S.A.
Mycotaxon, 2020Co-Authors: Everett M. Hansen, Jennifer M Davidson, Matteo Garbelotto, Paul Reeser, Kelly Ivors, L. Douhan, David M. RizzoAbstract:Phytophthora nemorosa, a new species isolated from Stem Cankers on two species of Fagaceae and leaves of various hosts, is described. The new species resembles P. ilicis with homothallic, amphigynous antheridia and deciduous, semi-papillate sporangia, and has a related ITS-DNA sequence. Symptoms and host range are similar to P. ramorum, cause of Sudden Oak Death and leaf blight and shoot dieback diseases in California and Oregon forests, although P. nemorosa does not appear to cause wide-spread mortality of oak trees.
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phytophthora species causing tanoak Stem Cankers in southwestern oregon
Plant Disease, 2008Co-Authors: Paul Reeser, Wendy Sutton, E M HansenAbstract:Tanoak (Lithocarpus densiflorus) is a principal host of Phytophthora ramorum, cause of sudden oak death (SOD), in the western United States (1). In the course of SOD surveys in southwestern Oregon, other Phytophthora species were encountered to be causing Stem Cankers on tanoak that were indistinguishable from those caused by P. ramorum. In Oregon, SOD is subject to quarantine and eradication. Aerial surveys are flown two or more times a year to locate symptomatic tanoaks, which are then examined from the ground to determine the cause of death. Isolations on selective media were attempted from all trees with Stem Cankers typical of Phytophthora. Phytophthora species were identified by morphological features and DNA sequencing of either internal transcribed spacer (ITS) or the mitochondrial COX spacer region. ITS sequences were compared with validated GenBank records, and COX spacer sequences were compared with known reference isolates in the OSU collection. From 2001 through 2006, Phytophthora spp. were i...
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phytophthora species associated with Stem Cankers on tanoak in southwestern oregon
In: Frankel Susan J.; Kliejunas John T.; Palmieri Katharine M. tech. coords. 2008. Proceedings of the sudden oak death third science symposium. Gen. T, 2008Co-Authors: Paul Reeser, Wendy Sutton, E M HansenAbstract:In effort to eradicate Phytophthora ramorum from Oregon forests, tanoak over its entire range in southwestern Oregon is surveyed intensively for Stem disease. Pieces of bark from the leading edge of tanoak Stem Cankers were plated on cornmeal agar amended with 10 ppm natamycin, 200 ppm a-ampicillin, and 10 ppm rifamycin SV (CARP) to favor the isolation of Phytophthora. Phytophthora ramorum was usually identified on the isolation plates based on the presence of characteristic hyphae, chlamydospores, and sporangia. Hyphae from the leading edge of other colonies resembling Phytophthora were isolated into pure culture. Isolates were grown out to obtain morphological features and DNA extracts for identification. Selected isolates were tested for pathogenicity by inoculating Stems of tanoak seedlings. Phytophthora species isolated from tanoak Stem Cankers include the following: P. cambivora, P. cinnamomi, P. species ?Pg chlamydo,? P. gonapodyides, P. nemorosa, and the proposed new species P. siskiyouensis. An additional isolate may represent a new species of Phytophthora that has not yet been described.
C L Mohammed - One of the best experts on this subject based on the ideXlab platform.
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pseudophacidium diselmae sp nov isolated from Stem Cankers on diselma archeri in tasmania australia
Australasian Plant Pathology, 2000Co-Authors: Z Q Yuan, T Rudman, C L MohammedAbstract:Fungi associated with Stem Cankers on Diselma archevi in central Tasmania were investigated. Three Ascomycetes (Massavia sp., Trernatosphaevia sp. and Pseudophacidium sp.) were observed on Stems with canker symptoms. The Pseudophacidium species was the most consistently isolated fungus from canker tissue and is proposed as P. diselnzae sp. nov
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pathogenicity of fungi associated with Stem Cankers of eucalypts in tasmania australia
Plant Disease, 1999Co-Authors: Z Q Yuan, C L MohammedAbstract:ABSTRACT Thirteen Stem-infecting fungal species, 11 from Tasmania and 2 from other parts of southeast Australia, were tested for their pathogenicity on 12-month-old seedlings of Eucalyptus nitens and E. globulus. They were classified into three groups based on their ability to cause Stem canker lesions following artificial inoculation: pathogenic species (Phoma sp., Endothia gyrosa, and Seiridium eucalypti), intermediate or weakly pathogenic species (Botryosphaeria sp., Seiridium papillatum, Pestalotiopsis neglecta, Zythiostroma sp., Ceuthospora innumera, Cytospora eucalypticola, and Wuestneia epispora), and nonpathogenic species (Dinemasporium strigosum, Seiridium unicorne, and Harknessia aff. eucalypti). The potential threat of canker fungi, especially Endothia gyrosa, to plantation forestry in Australia is discussed.
Wendy Sutton - One of the best experts on this subject based on the ideXlab platform.
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phytophthora species causing tanoak Stem Cankers in southwestern oregon
Plant Disease, 2008Co-Authors: Paul Reeser, Wendy Sutton, E M HansenAbstract:Tanoak (Lithocarpus densiflorus) is a principal host of Phytophthora ramorum, cause of sudden oak death (SOD), in the western United States (1). In the course of SOD surveys in southwestern Oregon, other Phytophthora species were encountered to be causing Stem Cankers on tanoak that were indistinguishable from those caused by P. ramorum. In Oregon, SOD is subject to quarantine and eradication. Aerial surveys are flown two or more times a year to locate symptomatic tanoaks, which are then examined from the ground to determine the cause of death. Isolations on selective media were attempted from all trees with Stem Cankers typical of Phytophthora. Phytophthora species were identified by morphological features and DNA sequencing of either internal transcribed spacer (ITS) or the mitochondrial COX spacer region. ITS sequences were compared with validated GenBank records, and COX spacer sequences were compared with known reference isolates in the OSU collection. From 2001 through 2006, Phytophthora spp. were i...
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phytophthora species associated with Stem Cankers on tanoak in southwestern oregon
In: Frankel Susan J.; Kliejunas John T.; Palmieri Katharine M. tech. coords. 2008. Proceedings of the sudden oak death third science symposium. Gen. T, 2008Co-Authors: Paul Reeser, Wendy Sutton, E M HansenAbstract:In effort to eradicate Phytophthora ramorum from Oregon forests, tanoak over its entire range in southwestern Oregon is surveyed intensively for Stem disease. Pieces of bark from the leading edge of tanoak Stem Cankers were plated on cornmeal agar amended with 10 ppm natamycin, 200 ppm a-ampicillin, and 10 ppm rifamycin SV (CARP) to favor the isolation of Phytophthora. Phytophthora ramorum was usually identified on the isolation plates based on the presence of characteristic hyphae, chlamydospores, and sporangia. Hyphae from the leading edge of other colonies resembling Phytophthora were isolated into pure culture. Isolates were grown out to obtain morphological features and DNA extracts for identification. Selected isolates were tested for pathogenicity by inoculating Stems of tanoak seedlings. Phytophthora species isolated from tanoak Stem Cankers include the following: P. cambivora, P. cinnamomi, P. species ?Pg chlamydo,? P. gonapodyides, P. nemorosa, and the proposed new species P. siskiyouensis. An additional isolate may represent a new species of Phytophthora that has not yet been described.