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David M. Gadoury - One of the best experts on this subject based on the ideXlab platform.
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Initiation, development, and survival of Cleistothecia of Podosphaera aphanis and their role in the epidemiology of strawberry powdery mildew.
Phytopathology, 2010Co-Authors: David M. Gadoury, Robert C. Seem, Belachew Asalf, M Catherine Heidenreich, M. L. Herrero, Mary Jean Welser, Anne Marte Tronsmo, Arne StensvandAbstract:A collection of four clonal isolates of Podosphaera aphanis was heterothallic and was composed of two mutually exclusive mating types. Cleistothecial initials approximately 20 to 30 microm in diameter were observed within 7 to 14 days after pairing of compatible isolates and developed into morphologically mature ascocarps within 4 weeks after initiation on both potted plants maintained in isolation and in field plantings in New York State and southern Norway. Ascospores progressed through a lengthy maturation process over winter, during which (i) the conspicuous epiplasm of the ascus was absorbed; (ii) the osmotic potential of the ascospore cytoplasm increased, resulting in bursting of prematurely freed spores in water; and, finally, (iii) resulting in the development of physiologically mature, germinable, and infectious ascospores. Release of overwintered ascospores from field collections was coincident with renewed plant growth in spring. Overwintered Cleistothecia readily dehisced when wetted and released ascospores onto glass slides, detached strawberry leaves, and leaves of potted plants. Plant material exposed to discharged ascospores developed macroscopically visible mildew colonies within 7 to 10 days while noninoculated controls remained mildew free. Scanning electron and light microscopy revealed that Cleistothecia of P. aphanis were enmeshed within a dense mat of hyphae on the persistent leaves of field-grown strawberry plants and were highly resistant to removal by rain while these leaves remained alive. In contrast, morphologically mature Cleistothecia on leaves of nine deciduous perennial plant species were readily detached by simulated rain and seemed adapted for passive dispersal by rain to other substrates. Contrary to many previous reports, Cleistothecia appear to be a functional source of primary inoculum for strawberry powdery mildew. Furthermore, they differ substantially from Cleistothecia of powdery mildews of many deciduous perennial plants in their propensity to remain attached to the persistent leaves of their host during the intercrop period.
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Maturation of Cleistothecia of Uncinula necator (powdery mildew) and release of ascospores in southern Australia
Australian Journal of Grape and Wine Research, 2000Co-Authors: L.m. Gee, David M. Gadoury, B. E. Stummer, L.t. Biggins, Eileen S. ScottAbstract:We paired genetically characterised isolates of U. necator under controlled conditions and raised the resultant Cleistothecia to maturity. Progeny were recovered from Cleistothecia formed in the glasshouse and growth room 97-110 days after Cleistothecial initials were observed. Cleistothecia collected from naturally infected leaves from vineyards in the Adelaide Plains and Langhorne Creek, South Australia, in March and April (autumn) 1998 and stored in the same vineyards, were induced to release ascospores in the laboratory between March 1998 and February 1999. This paper is the first report of Cleistothecia of U. necator releasing ascospores during summer, autumn and winter in southern Australia. Cleistothecia did not require a period of over-wintering in order to release ascospores that infected detached grapevine leaves in vitro. Furthermore, Cleistothecia that over-wintered in the field were triggered to release ascospores in the laboratory in spring. Release of ascospores in spring was coincident with observations of ascospore-derived infections in the Waite Campus vineyard, confirming that Cleistothecia provide an additional source of primary inoculum for powdery mildew in South Australia. Autumn release of ascospores suggests the possibility that U. necator may complete two sexual generations per year in Mediterranean climates, with consequent increased risks of development of fungicide resistance and changes in pathogenicity.
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Cleistothecia of Uncinula necator-An Additional Source of Inoculum in Italian Vineyards.
Plant disease, 1997Co-Authors: Paolo Cortesi, M. Bisiach, M. Ricciolini, David M. GadouryAbstract:Density and viability of populations of Cleistothecia of Uncinula necator from bark, leaves, and soil were determined in three vineyards in the Florence and Siena provinces of Tuscany for 3 years. A higher density of Cleistothecia was found on fallen leaves than on bark. However, the percentage of viable Cleistothecia was higher on bark. No viable Cleistothecia were recovered from soil. U. necator overwintered as mycelium in dormant infected buds, which gave rise to flag shoots, only in Santa Cristina, where 20 and 92 flag shoots per hectare were detected before bloom in 1994 and 1995, respectively. Disease incidence and severity increased similarly at Corti, Fornace, and at Santa Cristina, although powdery mildew epidemics started from ascospores only in Corti and Fornace, whereas flag shoots were present at Santa Cristina. Cleistothecia were formed in autumn in both 1994 and 1995, and their dispersal started in late September to mid-October, with the maximum number of Cleistothecia trapped in funnels during the second half of October. Cleistothecia appear to function as the sole source of primary inoculum for grape powdery mildew in some Italian vineyards and serve as additional sources of inoculum where the pathogen also overwinters in infected buds. In Australia but not in New York, the pathogen also overwinters as Cleistothecia on fallen leaves.
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Cleistothecia of Uncinula necator in Australia
1997Co-Authors: P. A. Magarey, David M. Gadoury, L.t. Biggins, R. W. Emmett, K. Clarke, M. F. Wachtel, T. J. Wicks, Robert C. SeemAbstract:Des cleistotheces viables et fonctionnels d'Uncinula necator sont repandus de nos jours en Australie, certainement a cause de la recente introduction de la seconde forme sexuelle. Comme reporte aux Etats-Unis, ils sont disperses par les pluies et survivent dans les bois. Contrairement aux observations effectuees aux Etats-Unis, des cleistotheces viables ont egalement ete isoles de debris de feuilles. L'importante survie des debris de feuilles, probablement due a l'absence de detritivores dans les vignobles, en fait une significative et supplementaire source d'inoculum pour l'hiver. Les precipitations faibles dans certaines regions d'Australie peuvent resulter en une incomplete dispersion des cleistotheces des feuilles vers le bois avant la chute des feuilles. Cependant, les precipitations sont suffisantes pour causer une ou plusieures liberations d'ascospores et ainsi causer l'extension de la maladie entre le debourrement et la floraison dans la plupart des regions viticoles d'Australie. L'irrigation peut causer des periodes additionnelles d'infections, mais peut egalement provoquer une liberation prematuree d'ascospores avant le debourrement.
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Parasitism of Uncinula necator Cleistothecia by the mycoparasite Ampelomyces quisqualis.
Phytopathology, 1995Co-Authors: S. P. Falk, David M. Gadoury, R. C. Pearson, Paolo Cortesi, Robert C. SeemAbstract:Parasitism of Uncinula necator Cleistothecia by the mycoparasite Ampelomyces quisqualis was widespread in the Vitaceae around New York State. Although A. quisqualis did not survive in naturally parasitized U. necator Cleistothecia on grape leaves, it did overwinter in parasitized Cleistothecia on the bark of grapevines. Although only 1% of the total population of Cleistothecia on bark was parasitized, the bark may still be an important site for overwintering of A. quisqualis since the mycoparasite is located adjacent to developing powdery mildew colonies on leaves, analogous to that of healthy Cleistothecia, which also overwinter on bark and release primary inoculum to infect emerging grape leaves. In vitro studies of parasitism of U. necator Cleistothecia showed that infection occurs only during early stages of development prior to or at the earliest stages of the formation of appendages but before darkening of the Cleistothecial wall. When A. quisqualis was applied to grapevines from colonized cotton-wick cultures suspended above vines, parasitism of Cleistothecia on leaves increased compared to naturally occurring parasitism, although during a season with high rainfall the level of parasitism was similar by the end of the season. The impact of increased parasitism was a reduction in the number of Cleistothecia dispersed from leaves to bark and a reduction (50 to 60%) in the number of Cleistothecia overwintering on bark of grapevines. Thus, biological control of grape powdery mildew with A. quisqualis may be further enhanced by a reduction in the level of overwintering inoculum for the next season.
Robert C. Seem - One of the best experts on this subject based on the ideXlab platform.
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Initiation, development, and survival of Cleistothecia of Podosphaera aphanis and their role in the epidemiology of strawberry powdery mildew.
Phytopathology, 2010Co-Authors: David M. Gadoury, Robert C. Seem, Belachew Asalf, M Catherine Heidenreich, M. L. Herrero, Mary Jean Welser, Anne Marte Tronsmo, Arne StensvandAbstract:A collection of four clonal isolates of Podosphaera aphanis was heterothallic and was composed of two mutually exclusive mating types. Cleistothecial initials approximately 20 to 30 microm in diameter were observed within 7 to 14 days after pairing of compatible isolates and developed into morphologically mature ascocarps within 4 weeks after initiation on both potted plants maintained in isolation and in field plantings in New York State and southern Norway. Ascospores progressed through a lengthy maturation process over winter, during which (i) the conspicuous epiplasm of the ascus was absorbed; (ii) the osmotic potential of the ascospore cytoplasm increased, resulting in bursting of prematurely freed spores in water; and, finally, (iii) resulting in the development of physiologically mature, germinable, and infectious ascospores. Release of overwintered ascospores from field collections was coincident with renewed plant growth in spring. Overwintered Cleistothecia readily dehisced when wetted and released ascospores onto glass slides, detached strawberry leaves, and leaves of potted plants. Plant material exposed to discharged ascospores developed macroscopically visible mildew colonies within 7 to 10 days while noninoculated controls remained mildew free. Scanning electron and light microscopy revealed that Cleistothecia of P. aphanis were enmeshed within a dense mat of hyphae on the persistent leaves of field-grown strawberry plants and were highly resistant to removal by rain while these leaves remained alive. In contrast, morphologically mature Cleistothecia on leaves of nine deciduous perennial plant species were readily detached by simulated rain and seemed adapted for passive dispersal by rain to other substrates. Contrary to many previous reports, Cleistothecia appear to be a functional source of primary inoculum for strawberry powdery mildew. Furthermore, they differ substantially from Cleistothecia of powdery mildews of many deciduous perennial plants in their propensity to remain attached to the persistent leaves of their host during the intercrop period.
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Cleistothecia of Uncinula necator in Australia
1997Co-Authors: P. A. Magarey, David M. Gadoury, L.t. Biggins, R. W. Emmett, K. Clarke, M. F. Wachtel, T. J. Wicks, Robert C. SeemAbstract:Des cleistotheces viables et fonctionnels d'Uncinula necator sont repandus de nos jours en Australie, certainement a cause de la recente introduction de la seconde forme sexuelle. Comme reporte aux Etats-Unis, ils sont disperses par les pluies et survivent dans les bois. Contrairement aux observations effectuees aux Etats-Unis, des cleistotheces viables ont egalement ete isoles de debris de feuilles. L'importante survie des debris de feuilles, probablement due a l'absence de detritivores dans les vignobles, en fait une significative et supplementaire source d'inoculum pour l'hiver. Les precipitations faibles dans certaines regions d'Australie peuvent resulter en une incomplete dispersion des cleistotheces des feuilles vers le bois avant la chute des feuilles. Cependant, les precipitations sont suffisantes pour causer une ou plusieures liberations d'ascospores et ainsi causer l'extension de la maladie entre le debourrement et la floraison dans la plupart des regions viticoles d'Australie. L'irrigation peut causer des periodes additionnelles d'infections, mais peut egalement provoquer une liberation prematuree d'ascospores avant le debourrement.
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Distribution and retention of Cleistothecia of Uncinula necator on bark of grapevines.
Plant Disease, 1995Co-Authors: Paolo Cortesi, David M. Gadoury, Robert C. Seem, R. C. PearsonAbstract:Clesitothecia of Uncinula necator were dispersed by late summer and early autumn rain to the bark of grapevines. Rain-dispersed ascocarps accumulated rapidly on bark during a 10-wk period and were then retained on bark through subsequent rain events between leaf abscission and budbreak the following spring. The density of populations on bark was significantly correlated (r = 0.72-0.88) with catches of Cleistothecia in filter-paper funnels attached to the trunk of grapevines. The density of populations on bark during winter was not correlated with several measures of disease incidence and severity from the previous growing season. We concluded that while incidence and severity may determine the potential population available for dispersal, rain events determine the actual efficiency of transfer from infected organs to the bark of the vine. The percentage of ascocarps that reacted positively with the fluorescent vital stain fluorescein diacetate ranged from 50 to 62% and did not change significantly during overwintering until Cleistothecia began to dehisce in spring. Therefore, the density and viability of populations of Cleistothecia on bark at the time of budbreak appear to have been determined at the time of leaf fall the previous autumn and were not modified by subsequent environmental conditions. The densest aggregations of Cleistothecia occurred on the cordons of cordon-trained vines, with successively lower densities occurring on the bark of the upper and lower trunks. The pruning and training system of vines of Vitis labrusca cv. Concord did not affect the density of populations of Cleistothecia on bark
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Parasitism of Uncinula necator Cleistothecia by the mycoparasite Ampelomyces quisqualis.
Phytopathology, 1995Co-Authors: S. P. Falk, David M. Gadoury, R. C. Pearson, Paolo Cortesi, Robert C. SeemAbstract:Parasitism of Uncinula necator Cleistothecia by the mycoparasite Ampelomyces quisqualis was widespread in the Vitaceae around New York State. Although A. quisqualis did not survive in naturally parasitized U. necator Cleistothecia on grape leaves, it did overwinter in parasitized Cleistothecia on the bark of grapevines. Although only 1% of the total population of Cleistothecia on bark was parasitized, the bark may still be an important site for overwintering of A. quisqualis since the mycoparasite is located adjacent to developing powdery mildew colonies on leaves, analogous to that of healthy Cleistothecia, which also overwinter on bark and release primary inoculum to infect emerging grape leaves. In vitro studies of parasitism of U. necator Cleistothecia showed that infection occurs only during early stages of development prior to or at the earliest stages of the formation of appendages but before darkening of the Cleistothecial wall. When A. quisqualis was applied to grapevines from colonized cotton-wick cultures suspended above vines, parasitism of Cleistothecia on leaves increased compared to naturally occurring parasitism, although during a season with high rainfall the level of parasitism was similar by the end of the season. The impact of increased parasitism was a reduction in the number of Cleistothecia dispersed from leaves to bark and a reduction (50 to 60%) in the number of Cleistothecia overwintering on bark of grapevines. Thus, biological control of grape powdery mildew with A. quisqualis may be further enhanced by a reduction in the level of overwintering inoculum for the next season.
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Reduction of powdery mildew and other diseases by over-the-trellis applications of lime sulfur to dormant grapevines
Plant Disease, 1994Co-Authors: David M. Gadoury, R. C. Pearson, D.g. Riegel, Robert C. Seem, C.m. Becker, Jay William PscheidtAbstract:From 72 to 96% of the ascospores within Cleistothecia of Uncinula necator were killed in the spring when exposed to lime sulfur (calcium polysulfide), copper sulfate, copper hydroxide, or copper oxychloride for 5 min in laboratory assays. Dinocap reduced viability in the same assay when the exposure time was more than 1 hr. Neither sulfur nor triadimefon significantly reduced viability. Cleistothecia collected in fall were not affected by the above fungicidal compounds in a 5-min exposure. One hour of exposure to lime sulfur or 8 hr of exposure to copper sulfate was required before ascospore viability was significantly reduced in the fall
Paolo Cortesi - One of the best experts on this subject based on the ideXlab platform.
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Cleistothecia of Uncinula necator-An Additional Source of Inoculum in Italian Vineyards.
Plant disease, 1997Co-Authors: Paolo Cortesi, M. Bisiach, M. Ricciolini, David M. GadouryAbstract:Density and viability of populations of Cleistothecia of Uncinula necator from bark, leaves, and soil were determined in three vineyards in the Florence and Siena provinces of Tuscany for 3 years. A higher density of Cleistothecia was found on fallen leaves than on bark. However, the percentage of viable Cleistothecia was higher on bark. No viable Cleistothecia were recovered from soil. U. necator overwintered as mycelium in dormant infected buds, which gave rise to flag shoots, only in Santa Cristina, where 20 and 92 flag shoots per hectare were detected before bloom in 1994 and 1995, respectively. Disease incidence and severity increased similarly at Corti, Fornace, and at Santa Cristina, although powdery mildew epidemics started from ascospores only in Corti and Fornace, whereas flag shoots were present at Santa Cristina. Cleistothecia were formed in autumn in both 1994 and 1995, and their dispersal started in late September to mid-October, with the maximum number of Cleistothecia trapped in funnels during the second half of October. Cleistothecia appear to function as the sole source of primary inoculum for grape powdery mildew in some Italian vineyards and serve as additional sources of inoculum where the pathogen also overwinters in infected buds. In Australia but not in New York, the pathogen also overwinters as Cleistothecia on fallen leaves.
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Parasitism of Uncinula necator Cleistothecia by the mycoparasite Ampelomyces quisqualis.
Phytopathology, 1995Co-Authors: S. P. Falk, David M. Gadoury, R. C. Pearson, Paolo Cortesi, Robert C. SeemAbstract:Parasitism of Uncinula necator Cleistothecia by the mycoparasite Ampelomyces quisqualis was widespread in the Vitaceae around New York State. Although A. quisqualis did not survive in naturally parasitized U. necator Cleistothecia on grape leaves, it did overwinter in parasitized Cleistothecia on the bark of grapevines. Although only 1% of the total population of Cleistothecia on bark was parasitized, the bark may still be an important site for overwintering of A. quisqualis since the mycoparasite is located adjacent to developing powdery mildew colonies on leaves, analogous to that of healthy Cleistothecia, which also overwinter on bark and release primary inoculum to infect emerging grape leaves. In vitro studies of parasitism of U. necator Cleistothecia showed that infection occurs only during early stages of development prior to or at the earliest stages of the formation of appendages but before darkening of the Cleistothecial wall. When A. quisqualis was applied to grapevines from colonized cotton-wick cultures suspended above vines, parasitism of Cleistothecia on leaves increased compared to naturally occurring parasitism, although during a season with high rainfall the level of parasitism was similar by the end of the season. The impact of increased parasitism was a reduction in the number of Cleistothecia dispersed from leaves to bark and a reduction (50 to 60%) in the number of Cleistothecia overwintering on bark of grapevines. Thus, biological control of grape powdery mildew with A. quisqualis may be further enhanced by a reduction in the level of overwintering inoculum for the next season.
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Distribution and retention of Cleistothecia of Uncinula necator on bark of grapevines.
Plant Disease, 1995Co-Authors: Paolo Cortesi, David M. Gadoury, Robert C. Seem, R. C. PearsonAbstract:Clesitothecia of Uncinula necator were dispersed by late summer and early autumn rain to the bark of grapevines. Rain-dispersed ascocarps accumulated rapidly on bark during a 10-wk period and were then retained on bark through subsequent rain events between leaf abscission and budbreak the following spring. The density of populations on bark was significantly correlated (r = 0.72-0.88) with catches of Cleistothecia in filter-paper funnels attached to the trunk of grapevines. The density of populations on bark during winter was not correlated with several measures of disease incidence and severity from the previous growing season. We concluded that while incidence and severity may determine the potential population available for dispersal, rain events determine the actual efficiency of transfer from infected organs to the bark of the vine. The percentage of ascocarps that reacted positively with the fluorescent vital stain fluorescein diacetate ranged from 50 to 62% and did not change significantly during overwintering until Cleistothecia began to dehisce in spring. Therefore, the density and viability of populations of Cleistothecia on bark at the time of budbreak appear to have been determined at the time of leaf fall the previous autumn and were not modified by subsequent environmental conditions. The densest aggregations of Cleistothecia occurred on the cordons of cordon-trained vines, with successively lower densities occurring on the bark of the upper and lower trunks. The pruning and training system of vines of Vitis labrusca cv. Concord did not affect the density of populations of Cleistothecia on bark
Gary G. Grove - One of the best experts on this subject based on the ideXlab platform.
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Perennation of Uncinula necator in Vineyards of Eastern Washington.
Plant disease, 2004Co-Authors: Gary G. GroveAbstract:Studies on the mode of perennation of Uncinula necator in Eastern Washington were conducted over a 4-year period. Evidence of perennation of U. necator in infected dormant buds was not evident during vineyard surveys conducted over the period. Cleistothecia retrieved from bark fissures and senesced leaves contained viable ascospores at bud burst and later. The proportion of Cleistothecia retrieved from bark that contained viable ascospores at bud burst ranged from 0.19 to 0.48, 0.09 to 0.72, 0.18 to 0.22, and 0.48 to 0.67 in 1998, 1999, 2000, and 2001, respectively. Viability of Cleistothecia retrieved from senesced leaves in two vineyards at bud burst was 0.41 and 0.40 in 1998 and was 0.5 and 0.4 in 1999. Ascospore release in lab studies occurred from the late-dormant stage through the prebloom and (in some cases) the bloom stages. The initial ascosporic infection of Chardonnay leaves began at the late-dormant stage; colony numbers then declined through the prebloom and bloom stages. In vineyard studies, ascospores were trapped as late as 70 days after bud burst during rain events of 3.9 to 9.6 mm. Detection of ascospores in vineyard air preceded the initial occurrence of powdery mildew symptoms and signs and the occurrence of conidia in volumetric spore traps by several days. Cleistothecia are the only known source of primary inoculum in the grape-production regions of Eastern Washington.
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Overwinter survival of Podosphaera clandestina in Eastern Washington
Phytopathology, 1991Co-Authors: Gary G. Grove, R. J. BoalAbstract:Podosphaera clandestina survived winter as Cleistothecia on senescent cherry leaves on the orchard floor or trapped in tree crotches, as Cleistothecia in partially decomposed leaves trapped in tree crotches, or as Cleistothecia trapped in bark crevices. Ascocarp viability ranged from 55−90% in early February to 5−33% in mid-May. Inoculation of cherry seedlings with overwintered Cleistothecia collected from early March through mid-May resulted in infection, with the largest number of mildew colonies resulting from inoculation with Cleistothecia that were collected around bud burst. Ascospore release began 1 mo before bud burst and continued until after the bloom period (...)
M. T. Mcgrath - One of the best experts on this subject based on the ideXlab platform.
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Heterothallism in Sphaerotheca fuliginea
Mycologia, 1994Co-Authors: M. T. McgrathAbstract:Sphaerotheca fuliginea infecting cucurbits was demonstrated to be heterothallic. Isolates were ob? tained from pumpkin (Cucurbita pepo) in New York and summer squash (C. pepo) in Florida. Heterothal? lism was demonstrated by growing isolates singly or in pairs on detached leaves of summer squash in culture. These leaves were in two joined petri dishes with the leaf blade in the upper dish and the petiole in soil in the lower dish. Cleistothecia formed only when two compatible isolates were grown together. Six isolates were assigned to mating type MAT 1-2 and 59 were assigned to MAT 1-1. Special stimulatory conditions, such as low temperature or senescence of host tissue, were not required for Cleistothecial formation on de? tached leaves or on greenhouse-grown plants. Hyaline Cleistothecia were observed as soon as 8 days after inoculation and became brown in 1-5 days. Unequal distribution of mating types may at least partially ac- count for the rare occurrence of Cleistothecia world? wide.