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D.j. Van Der Gaag - One of the best experts on this subject based on the ideXlab platform.
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Oospore populations of Peronospora viciae : quantification, germinability and survival
1997Co-Authors: D.j. Van Der GaagAbstract:Peronospora viciae causes downy mildew on pea, field and broad bean. Two pathogens can be distinguished, P. viciae f.sp. pisi on pea (Pisum sativum) and P. viciae f. sp. fabae on field and broad bean (Vicia faba). These pathogens form resting spores, called Oospores, in their host plant tissue. The Oospores infest the soil after decomposition of the surrounding plant tissue and are the means by which the pathogens survive in the absence of host plants. In the present thesis aspects of the population biology of the Oospores were investigated. Numbers of Oospores were determined by extraction from plant tissue or soil. A vital stain test and a germination assay were used to assess viability and germinability of Oospore populations. Monoconidial isolates of the two pathogens were able to produce Oospores in monoculture and thus both pathogens are homothallic. P. viciae f.sp. pisi had a minimum temperature of about 10°C for Oospore production and P. viciae f.sp. fabae below 5°C Dry-stored Oospores of P. viciae f.sp. pisi germinated in water and appeared independent of an exogenous chemical stimulus for germination. Germinability of these Oospores increased with Oospore age up to a certain point and was related to their infectivity in a bioassay. Dry-stored Oospores of P. viciae f.sp. fabae did neither germinate in water nor did they infect seedlings in a bioassay. After incorporation in field soil, Oospore populations of both pathogens declined rapidly, and small, probably non-random, proportions of the original Oospore populations survived for more than a year. The ability of Oospores of P. viciae f.sp. pisi to germinate in water declined rapidly after incorporation in soil. Low percentages of Oospores extracted from soil germinated in water, but relatively high disease incidences were obtained after inoculation of pea seeds with these Oospores which suggested that soilexposed Oospores become dependent on a chemical stimulus for germination. Oospores of P. viciae f.sp. fabae were infective after incubation in field soil for two years.
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Extraction of Oospores of Peronospora viciae from soil.
Plant Pathology, 1997Co-Authors: D.j. Van Der Gaag, H. D. FrinkingAbstract:A method for the extraction of Oospores of Peronospora viciae from soil is described. Approximately 75% of the Oospores added to silty clay loam and loamy sand soil samples were recovered. Percentage recovery was independent of Oospore density. This extraction method did not affect viability as determined by the tetrazolium bromide test and a germination assay and may therefore be used to study survival of Oospores. Numbers of Oospores extracted from soil samples taken from seven fields naturally infested with Oospores of P. viciae f.sp. pisi ranged from 2 to 21 Oospores per g soil. Oospore density was not significantly correlated with disease incidence as determined by a bioassay.
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Survival characteristics of Oospore populations of Peronospora viciae f.sp. pisi in soil
Plant Pathology, 1997Co-Authors: D.j. Van Der Gaag, H. D. FrinkingAbstract:Survival and germinability of Oospore populations of Peronospora viciae f.sp. pisi in soil were investigated. The percentage survival was assessed using the vital stain tetrazolium bromide. Germinability was defined as the percentage of Oospores that germinated in water. Oospores 1–3 weeks old, embedded in plant tissue, were incorporated in a loamy sand or silt-loam soil and incubated at 3, 10 or 20°C or stored dry at 20°C and 30% RH. The percentage of surviving Oospores in soil decreased rapidly with or after decomposition of the surrounding plant tissue at 10 and 20°C. After 29 weeks less than 10% of the Oospores had survived. At 3°C, survival was 25% or more after 29 weeks. Germinability of the Oospores was 3% at time of incorporation and had increased to a maximum of 50% after 4 weeks in the loamy sand soil. Increase in germinability of the dry-stored Oospores was significantly later than that of the soil-incubated Oospores. In soil, the initial increase in germinability was followed by a decline after decomposition of the surrounding plant tissue. In order to investigate survival of Oospores under natural conditions, ground tissue or pod pieces of pea plants containing Oospores 7 or 5 months old, respectively, were incorporated in two loamy sand soils or a silt loam soil in field plots. The surrounding plant tissue decomposed within 4 weeks and the percentage of surviving Oospores decreased to less than 6% after a year. Survival of Oospore populations was generally well described by the lognormal model, indicating that the risk of Oospore death initially increased before decreasing later. Germinability of the Oospore populations from ground tissue and pod pieces, 61 and 62% at incorporation, decreased rapidly after incorporation in soil. Oospores extracted from the silt-loam soil germinated poorly in water but caused high disease incidences in a bioassay, suggesting that Oospores had become dependent on the host plant for germination.
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Homothallism in Peronospora viciae f.sp. pisi and the effect of temperature on Oospore production
Plant Pathology, 1996Co-Authors: D.j. Van Der Gaag, H. D. FrinkingAbstract:Monoconidial cultures derived from seven P. viciae f.sp. pisi isolates, obtained from different countries, were able to produce Oospores. Apparently, these isolates were homothallic. Oospore production of one isolate was studied at 5, 10, 15 and 20°C in systemically colonized shoots, and in local lesions on leaflets, stem parts and pods of the Pisum sativum cv. Kelvedon Wonder. The number of Oospores produced per gram systemically colonized tissue increased with temperature. In lesions of leaflets and of stem parts, including tendrils, petioles and main stem, most Oospores were produced at 20°C. At 10°C, a few Oospores were found in stem parts but none in leaflet lesions. At 5°C, no Oospores were formed at all. In pods, more Oospores were produced at 15 and 20°C than at 10°C, but the effect of temperature on the numbers of Oospores was smaller than in the other plant parts. Oospores formed at lower temperatures were larger than those formed at higher temperatures. At 20°C, similar Oospore densities were found in leaflet lesions of three cultivars widely differing in resistance to downy mildew.
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Production of Oospores by Peronospora viciae f.sp. fabae
European Journal of Plant Pathology, 1993Co-Authors: D.j. Van Der Gaag, H. D. Frinking, C. F. GeerdsAbstract:Oospore production inVicia faba, cv. Metissa, was quantified in the field after plants had been inoculated with a sporangium suspension of a homothallic isolate ofPeronospora viciae f.sp.fabae. Oospores were produced abundantly during the hole growing season from 3 weeks after inoculation on. Oospores were found in all plant parts above soil level, except in the seeds. Most Oospores were found in the leaves. Less Oospores were formed in leaves inoculated in an older stage than in those inoculated in a younger stage. Towards the end of the season, in August, numbers of Oospores in pods strongly increased.
Yigal Cohen - One of the best experts on this subject based on the ideXlab platform.
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Oospore Formation by Phytophthora infestans in Potato Tubers.
Phytopathology, 2001Co-Authors: Aaron Levin, A. Baider, Evgenia Rubin, Ulrich Gisi, Yigal CohenAbstract:ABSTRACT The ability of Phytophthora infestans, the causal agent of potato and tomato late blight, to produce Oospores in potato tuber tissue was studied in the field and under laboratory conditions. In 1998 and 2000 field experiments, the canopy of potato cvs. Alpha and Mondial, respectively, were coinoculated with A1 + A2 sporangia of the fungus, and the infected tubers collected at harvest were examined for the presence of Oospores. In 1998, only 2 of 90 infected tubers had Oospores, whereas none of the 90 tubers examined in 2000 had any Oospores. In the latter experiment, infected tubers kept in storage up to 12 weeks after harvest had no Oospores. Artificial co-inoculations of whole tubers with A1 + A2 sporangia resulted only rarely in the formation of Oospores inside the tubers. Co-inoculations of potato tuber discs taken from dormant tubers 0 to 16 weeks after harvest failed to support any Oospore production, whereas discs taken from sprouting tubers of ≥18 weeks after harvest allowed Oospores to f...
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Oospore Production of Phytophthora infestans in Potato and Tomato Leaves.
Phytopathology, 1997Co-Authors: Yigal Cohen, S. Farkash, Z. Reshit, A. BaiderAbstract:ABSTRACT Fungal, host, and environmental factors affecting sexual reproduction of Phytophthora infestans in planta were studied. Intact and detached leaves were coinoculated with sporangia of various combinations of A1 and A2 mating-type isolates; leaves were incubated under various conditions, and Oospore production was estimated microscopically within whole, clarified leaflets. Some A1 + A2 isolate combinations were more reproductive than others, whereas some potato genotypes better supported Oospore formation than others. Tomato usually supported more Oospore formation than potato. To induce Oospore formation, A1 and A2 sporangia were usually mixed at a 1:1 ratio. Ratios of 1:19 to 19:1, however, also allowed abundant production of Oospores. Optimal temperatures for sexual sporulation ranged from 8 to 15°C, but Oospores also were produced at 23°C. Oogonia developed 5 to 6 days after sporangial coinoculation, and Oospores developed after 8 to 10 days. Light had little effect on Oospore formation in both...
H. D. Frinking - One of the best experts on this subject based on the ideXlab platform.
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Extraction of Oospores of Peronospora viciae from soil.
Plant Pathology, 1997Co-Authors: D.j. Van Der Gaag, H. D. FrinkingAbstract:A method for the extraction of Oospores of Peronospora viciae from soil is described. Approximately 75% of the Oospores added to silty clay loam and loamy sand soil samples were recovered. Percentage recovery was independent of Oospore density. This extraction method did not affect viability as determined by the tetrazolium bromide test and a germination assay and may therefore be used to study survival of Oospores. Numbers of Oospores extracted from soil samples taken from seven fields naturally infested with Oospores of P. viciae f.sp. pisi ranged from 2 to 21 Oospores per g soil. Oospore density was not significantly correlated with disease incidence as determined by a bioassay.
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Survival characteristics of Oospore populations of Peronospora viciae f.sp. pisi in soil
Plant Pathology, 1997Co-Authors: D.j. Van Der Gaag, H. D. FrinkingAbstract:Survival and germinability of Oospore populations of Peronospora viciae f.sp. pisi in soil were investigated. The percentage survival was assessed using the vital stain tetrazolium bromide. Germinability was defined as the percentage of Oospores that germinated in water. Oospores 1–3 weeks old, embedded in plant tissue, were incorporated in a loamy sand or silt-loam soil and incubated at 3, 10 or 20°C or stored dry at 20°C and 30% RH. The percentage of surviving Oospores in soil decreased rapidly with or after decomposition of the surrounding plant tissue at 10 and 20°C. After 29 weeks less than 10% of the Oospores had survived. At 3°C, survival was 25% or more after 29 weeks. Germinability of the Oospores was 3% at time of incorporation and had increased to a maximum of 50% after 4 weeks in the loamy sand soil. Increase in germinability of the dry-stored Oospores was significantly later than that of the soil-incubated Oospores. In soil, the initial increase in germinability was followed by a decline after decomposition of the surrounding plant tissue. In order to investigate survival of Oospores under natural conditions, ground tissue or pod pieces of pea plants containing Oospores 7 or 5 months old, respectively, were incorporated in two loamy sand soils or a silt loam soil in field plots. The surrounding plant tissue decomposed within 4 weeks and the percentage of surviving Oospores decreased to less than 6% after a year. Survival of Oospore populations was generally well described by the lognormal model, indicating that the risk of Oospore death initially increased before decreasing later. Germinability of the Oospore populations from ground tissue and pod pieces, 61 and 62% at incorporation, decreased rapidly after incorporation in soil. Oospores extracted from the silt-loam soil germinated poorly in water but caused high disease incidences in a bioassay, suggesting that Oospores had become dependent on the host plant for germination.
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Homothallism in Peronospora viciae f.sp. pisi and the effect of temperature on Oospore production
Plant Pathology, 1996Co-Authors: D.j. Van Der Gaag, H. D. FrinkingAbstract:Monoconidial cultures derived from seven P. viciae f.sp. pisi isolates, obtained from different countries, were able to produce Oospores. Apparently, these isolates were homothallic. Oospore production of one isolate was studied at 5, 10, 15 and 20°C in systemically colonized shoots, and in local lesions on leaflets, stem parts and pods of the Pisum sativum cv. Kelvedon Wonder. The number of Oospores produced per gram systemically colonized tissue increased with temperature. In lesions of leaflets and of stem parts, including tendrils, petioles and main stem, most Oospores were produced at 20°C. At 10°C, a few Oospores were found in stem parts but none in leaflet lesions. At 5°C, no Oospores were formed at all. In pods, more Oospores were produced at 15 and 20°C than at 10°C, but the effect of temperature on the numbers of Oospores was smaller than in the other plant parts. Oospores formed at lower temperatures were larger than those formed at higher temperatures. At 20°C, similar Oospore densities were found in leaflet lesions of three cultivars widely differing in resistance to downy mildew.
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Production of Oospores by Peronospora viciae f.sp. fabae
European Journal of Plant Pathology, 1993Co-Authors: D.j. Van Der Gaag, H. D. Frinking, C. F. GeerdsAbstract:Oospore production inVicia faba, cv. Metissa, was quantified in the field after plants had been inoculated with a sporangium suspension of a homothallic isolate ofPeronospora viciae f.sp.fabae. Oospores were produced abundantly during the hole growing season from 3 weeks after inoculation on. Oospores were found in all plant parts above soil level, except in the seeds. Most Oospores were found in the leaves. Less Oospores were formed in leaves inoculated in an older stage than in those inoculated in a younger stage. Towards the end of the season, in August, numbers of Oospores in pods strongly increased.
R D Peters - One of the best experts on this subject based on the ideXlab platform.
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variation in virulence host specificity hyphal growth rate and size of the aplerotic zone in successive single zOospore and single Oospore progenies of aphanomyces euteiches
Canadian Journal of Plant Pathology-revue Canadienne De Phytopathologie, 2000Co-Authors: H Shang, C R Grau, R D PetersAbstract:Variation in virulence, host specificity, hyphal growth rate, and size of the aplerotic zone were studied in Aphanomyces euteiches using successive single-zOospore progeny (asexual reproduction) and single-Oospore progeny from selling (sexual reproduction). No variation in virulence or host specificity to pea or bean was found in generations of single-zOospore or single-Oospore isolates derived from four field isolates. In each isolate, hyphal growth rate and size of the aplerotic zone were relatively stable traits among six generations of single-spore progeny; the phenotypes of progeny remained similar to parental phenotypes. The traits were found to be the same within, but different between, two pea and two bean pathotype isolates. Stable randomly amplified polymorphic DNA (RAPD) markers associated with different isolates were selected in successive generations of zOospore and selfed Oospore progeny and could be used to distinguish the four isolates. Results suggest that the genes involved in determinin...
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Oospore germination of Aphanomyces euteiches in root exudates and on the rhizoplanes of crop plants
Plant disease, 2000Co-Authors: H Shang, Craig R. Grau, R D PetersAbstract:A technique was developed that allows prolific production, easy collection, and increased germination frequency of single Oospores of Aphanomyces euteiches. The influence of root exudates and roots of various plant species, including pea, bean, alfalfa, oat, soybean, corn, and tomato, on germination of A. euteiches Oospores also was studied. Compared with a sterile, deionized water control, root exudates from several hosts were only slightly effective in stimulating Oospore germination, since only 0 to 11.1% of Oospores exposed to various exudates germinated. By contrast, Oospores placed directly on plant roots germinated at higher frequencies. Oospores of pea pathotype isolates P30 and P46 germinated at a greater frequency (30.6 to 61.1%) on pea, bean, and oat roots than on roots of any of the other plant species tested. Oospores of bean pathotype isolates GB33 and GB71 had a higher germination frequency (47.2 to 52.8%) on bean roots than on the roots of the other plant species tested. A higher percentage of Oospores germinated if placed on lateral roots as opposed to taproots of pea and bean. A higher percentage of Oospores of bean pathotype isolates and one pea pathotype isolate germinated on 10-day-old rather than on 20-day-old roots of bean. Therefore, pea and bean roots can be used effectively to germinate Oospores of pea and bean isolates of A. euteiches, respectively. This technique will be valuable for studies of sexual reproduction and genetics of A. euteiches.
William E. Fry - One of the best experts on this subject based on the ideXlab platform.
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Formation of Phytophthora infestans Oospores in Nature on Tubers in Central Mexico
Plant disease, 2002Co-Authors: Sylvia Patricia Fernández-pavía, Niklaus J. Grünwald, William E. FryAbstract:Oospore formation by Phytophthora infestans in nature has been detected on potato leaflets in central Mexico (1), but there are no reports of Oospore formation on tubers. A severe late blight epidemic occurred in Calimaya, Mexico, in fields where potato cv. Alpha was planted during the summer of 2000. Yield was reduced despite numerous applications of fungicide. Four hundred potato tubers left in the field were collected from the upper 10 cm of soil and examined for late blight symptoms. Tubers with soft and dry rot symptoms were observed, but symptoms of pink rot (Phytophthora erythroseptica) were not found. Four percent of the tubers showed late blight symptoms. Sections of 10 tubers with late blight symptoms were air-dried for 2 weeks in the laboratory and homogenized with a mortar and pestle. Glycerol was added to the homogenized tissue and observed microscopically. Aplerotic Oospores (10 to 15 Oospores per tuber) with amphyginous antheridia typical of P. infestans were observed. P. mirabilis morphologically similar to P. infestans is present in the area but it does not infect potato tubers. The number of Oospores observed in our tuber sample was much lower than the number reported on leaflets (>1,000 Oospores per leaflet) in the Toluca Valley. Low numbers of Oospores have been reported on tubers artificially inoculated with P. infestans under field conditions (2). Infected tubers left in the field may act as a source of primary inoculum. To our knowledge, this is the first report of Oospores of P. infestans found on tubers in Mexico under natural field conditions. References: (1) M. E. Gallegly and J. Galindo. Phytopathology 48:274, 1958. (2) A. Levin et al. Phytopathology 91:579, 2001.
