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Wayne F Wilcox - One of the best experts on this subject based on the ideXlab platform.
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effects of diffuse colonization of grape berries by Uncinula Necator on bunch rots berry microflora and juice and wine quality
Phytopathology, 2007Co-Authors: David M. Gadoury, Robert C. Seem, Wayne F Wilcox, Thomas Henickkling, Lorenza Conterno, Andrea Day, Andrea FickeAbstract:ABSTRACT Production of grape (principally cultivars of Vitis vinifera) for high-quality wines requires a high level of suppression of powdery mildew (Uncinula Necator syn. Erysiphe Necator). Severe infection of either fruit or foliage has well-documented and deleterious effects upon crop and wine quality. We found that berries nearly immune to infection by U. Necator due to the development of ontogenic resistance may still support diffuse and inconspicuous mildew colonies when inoculated ≈3 weeks post-bloom. Fruit with diffuse mildew colonies appear to be healthy and free of powdery mildew in late-season vineyard assessments with the naked eye. Nonetheless, presence of these colonies on berries was associated with (i) elevated populations of spoilage microorganisms; (ii) increased evolution of volatile ethyl acetate, acetic acid, and ethanol; (iii) increased infestation by insects known to be attracted to the aforementioned volatiles; (iv) increased rotting by Botrytis cinerea; and (v) increased frequency...
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sensitivity to azoxystrobin among isolates of Uncinula Necator baseline distribution and relationship to myclobutanil sensitivity
Plant Disease, 2002Co-Authors: Francis P Wong, Wayne F WilcoxAbstract:Two hundred fifty-six single-conidial chain isolates of Uncinula Necator were assayed for their sensitivity to azoxystrobin and myclobutanil. These isolates were collected from two sites in New York in 1999: an "organic" vineyard where no synthetic fungicides have been used (baseline population) and a commercial vineyard having a history of compromised powdery mildew control with myclobutanil (demethylation inhibitor [DMI]-resistant population). Mean coefficients of variance for a leaf disk assay used to test fungicide sensitivities were 31% for azoxystrobin and 41% for myclobutanil. Baseline ED50 values ranged from 0.0037 to 0.028 μg/ml (mean 0.0097μg/ml) for azoxystrobin and from 0.0049 to 0.69 μg/ml (mean 0.075 μg/ml) for myclobutanil. A shift in the mean ED50 value for azoxystrobin to 0.018 μg/ml was observed in the DMI-resistant population; with the strongest shift observed for isolates collected from vines treated exclusively with myclobutanil (0.024 μg/ml). For the 256 tested isolates, there was a moderate, but statistically significant, correlation between azoxystrobin and myclobutanil sensitivities (R2 = 0.36, P < 0.001). Tests with three other strobilurin fungicides (kresoxim-methyl, pyraclostrobin, and trifloxystrobin) indicate clear differences in the intrinsic activity of these compounds against U. Necator, and the applicability of the methods developed with azoxystrobin for assays with pyraclostrobin and trifloxystrobin. Isolates from the high and low ends of the azoxystrobin sensitivity distribution (15× difference in mean ED50 values) were equally controlled in planta by protectant or postinfection treatment with azoxystrobin at 250 μg a.i./ml, but postinfection application at lower rates (2.5 and 25 μg a.i./ml) resulted in a 41 and 44% decrease, respectively, in the control of the low-sensitivity isolates versus high-sensitivity isolates. The results of this study document the baseline sensitivity distribution of U. Necator to azoxystrobin, provide evidence of partial cross-sensitivity between azoxystrobin and myclobutanil, and illustrate the potential selection for individuals with reduced sensitivity (quantitative range) to azoxystrobin by postinfection application and reduced rates of this fungicide.
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distributions of sensitivities to three sterol demethylation inhibitor fungicides among populations of Uncinula Necator sensitive and resistant to triadimefon
Phytopathology, 1997Co-Authors: Eugene O Erickson, Wayne F WilcoxAbstract:ABSTRACT Single-conidial isolates of Uncinula Necator from (i) a population representing two vineyards with no previous exposure to sterol demethylation inhibitor (DMI) fungicides (“unexposed,” n = 77) and (ii) a population representing two vineyards in which powdery mildew was poorly controlled by triadimefon after prolonged DMI use (“selected,” n = 82) were assayed to determine distributions of sensitivities to the DMI fungicides triadimenol (the active form of triadimefon), myclobutanil, and fenarimol. Median 50% effective dose (ED50) values (micrograms per milliliter) in the selected versus unexposed populations were 0.06 versus 1.9 for triadimenol, 0.03 versus 0.23 for myclobutanil, and 0.03 versus 0.07 for fenarimol, respectively. Isolates were grouped into sensitivity classes according to their ED50 values, and those from the selected population were categorized as resistant if the frequency of their sensitivity class had increased significantly relative to levels found in the unexposed population ...
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distributions of sensitivities to three sterol demethylation inhibitor fungicides among populations of Uncinula Necator sensitive and resistant to triadimefon
Phytopathology, 1997Co-Authors: Eugene O Erickson, Wayne F WilcoxAbstract:ABSTRACT Single-conidial isolates of Uncinula Necator from (i) a population representing two vineyards with no previous exposure to sterol demethylation inhibitor (DMI) fungicides ("unexposed," n = 77) and (ii) a population representing two vineyards in which powdery mildew was poorly controlled by triadimefon after prolonged DMI use ("selected," n = 82) were assayed to determine distributions of sensitivities to the DMI fungicides triadimenol (the active form of triadimefon), myclobutanil, and fenarimol. Median 50% effective dose (ED(50)) values (micrograms per milliliter) in the selected versus unexposed populations were 0.06 versus 1.9 for triadimenol, 0.03 versus 0.23 for myclobutanil, and 0.03 versus 0.07 for fenarimol, respectively. Isolates were grouped into sensitivity classes according to their ED(50) values, and those from the selected population were categorized as resistant if the frequency of their sensitivity class had increased significantly relative to levels found in the unexposed population (ED(50) values exceeding 0.56, 0.18, and 0.18 mug/ml for triadimenol, myclobutanil, and fenarimol, respectively). Of the 76 isolates defined as resistant to triadimenol, 64% were classified as cross-resistant to myclobutanil, 18% were classified as cross-resistant to fenarimol, and 17% were classified as resistant to all three fungicides; 25% of the isolates classified as resistant to myclobutanil also were classified as resistant to fenarimol. Similar cross-resistance relationships were revealed when all isolates were examined by regressing log ED(50) values for each fungicide against those for the remaining two fungicides to determine the correlation coefficients (e.g., r = 0.85 for triadimenol versus myclobutanil and 0.56 for triadimenol versus fenarimol). The restricted levels of cross-resistance indicated by these data, particularly between fenarimol and the other two fungicides, is in sharp contrast to the high levels of cross-resistance among DMIs reported for some other pathogens and has significant implications with respect to programs for managing grapevine powdery mildew and DMI resistance.
W D Gubler - One of the best experts on this subject based on the ideXlab platform.
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sensitivity of california isolates of Uncinula Necator to trifloxystrobin and spiroxamine and update on triadimefon sensitivity
Plant Disease, 2004Co-Authors: Thomas C Miller, W D GublerAbstract:ABSTRACT Sensitivities of Uncinula Necator to spiroxamine and trifloxystrobin were established by assay of 36 and 35 isolates, respectively, recovered from California grape vineyards in 2002 and increased as single-spore lines for laboratory testing. Twenty-nine single-spore isolates also were evaluated for levels of sensitivity to the fungicide triadimefon to determine if there had been a reversion to sensitivity following the development of resistance in 1986. Although triadimefon use was limited after 1992, other demethylation inhibitor (DMI) fungicides (fenarimol and myclobutanil) were used extensively in California vineyards. For spiroxamine, the sample mean value of the median effective concentration (EC50 value) was 365 μg/liter (95% confidence interval [CI] from 251 to 531 μg/liter) and values were distributed log-normally. The corresponding mean for trifloxystrobin was 12.8 μg/liter bounded by 8.9 to 18.5 μg/liter for the 95% CI. State-wide, the triadimefon mean EC50 was 8.8 mg/liter, bounded by ...
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the distribution of early season grapevine shoots infected by Uncinula Necator from year to year a case study in two california vineyards
American Journal of Enology and Viticulture, 2000Co-Authors: H L Ypema, W D GublerAbstract:Uncinula Necator (Schw.) Burr., the causal agent of powdery mildew on grapevines ( Vitis vinifera L.), survives the winter in the San Joaquin Valley in California predominantly by perennation in buds. Infected shoots arising from these buds (flag shoots) are important inoculum sources early in the growing season. Studies were conducted in two San Joaquin Valley vineyard sites over a three-year period to determine whether infected shoots tended to occur on the same vines from year to year. The studies also had the goal to determine whether the occurrence of infected shoots was influenced by the location of spurs retained from shoots infected the previous year. The number of vines with infected shoots in two consecutive years was greater than expected for a random infection process. The incidence of infected shoots arising from spurs retained from shoots infected the previous year was significantly greater than expected for a random shoot infection process. However, most infected shoots arose on spurs that were not infected the previous year, and they were not clustered around spurs retained from shoots infected the previous year. Removal of spurs retained from shoots infected the previous season during dormancy, or removal of flag shoots early in the season as a control measure by itself will probably not sufficiently reduce flag shoots incidence the following years
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long term effect of temperature and triadimefon on proliferation of Uncinula Necator implications for fungicide resistance and disease risk assessment
Plant Disease, 1997Co-Authors: H L Ypema, W D GublerAbstract:ABSTRACT Triadimefon has been used in California to control Uncinula Necator, causal agent of grape powdery mildew, since 1982. Instances of unsatisfactory control have occurred mainly in the cooler coastal areas of California. The effect of temperature and application of triadimefon was investigated over a 53-day-period on two U. Necator isolates, sensitive and resistant to triadimefon. At 15°C, 25°C, or temperatures fluctuating between 15 and 25°C, in absence of triadimefon, the isolates continued to produce high numbers of conidia for the entire duration of the experiment. Sporulation declined at daily maximum temperatures of 32°C for 6 h, 36°C for 3 h, and 40°C for 1 h, but was detectable when the experiment was terminated. At these temperature regimes, sporulation of the triadimefon-treated sensitive isolate ceased after 23 days. When treated with triadimefon, sporulation of the resistant isolate was comparable to that of the water-treated control. At daily maximum temperatures of 32°C for 11 h, 36°C...
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sensitivity of Uncinula Necator to benomyl triadimefon myclobutanil and fenarimol in california
Plant Disease, 1997Co-Authors: H L Ypema, M Ypema, W D GublerAbstract:ABSTRACT Sensitivity of Uncinula Necator subcultures to benomyl and the demethylation-inhibiting (DMI) fungicides triadimefon, myclobutanil, and fenarimol was assessed in 1993, 1994, and 1995 with leaf disk bioassays. In 1993, 1994, and 1995, 81.8, 96, and 96.7% of the subcultures, respectively, did not grow on leaf disks treated with 30 mg of benomyl per liter, whereas growth of the remaining subcultures was inhibited by more than 90%. Median EC50 values of triadimefon, myclobutanil, and fenarimol decreased from 1993 to 1994, and those of triadimefon decreased again from 1994 to 1995. In the same period, median EC50 values of all three DMI fungicides increased in a vineyard never exposed to DMI fungicides. The highest means and ranges of EC50 values found were those of triadimefon. Means and ranges were lower for myclobutanil and lowest for fenarimol, reflecting differences in inherent activities of the fungicides and po-tential for development of resistance. Pairwise correlations between EC50 values of ...
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sensitivity of Uncinula Necator to benomyl triadimefon myclobutanil and fenarimol in california
Plant Disease, 1997Co-Authors: H L Ypema, M Ypema, W D GublerAbstract:Sensitivity of Uncinula Necator subcultures to benomyl and the demethylation-inhibiting (DMI) fungicides triadimefon, myclobutanil, and fenarimol was assessed in 1993, 1994, and 1995 with leaf disk bioassays. In 1993, 1994, and 1995, 81.8, 96, and 96.7% of the subcultures, respectively, did not grow on leaf disks treated with 30 mg of benomyl per liter, whereas growth of the remaining subcultures was inhibited by more than 90%. Median EC50 values of triadimefon, myclobutanil, and fenarimol decreased from 1993 to 1994, and those of triadimefon decreased again from 1994 to 1995. In the same period, median EC50 values of all three DMI fungicides increased in a vineyard never exposed to DMI fungicides. The highest means and ranges of EC50 values found were those of triadimefon. Means and ranges were lower for myclobutanil and lowest for fenarimol, reflecting differences in inherent activities of the fungicides and po-tential for development of resistance. Pairwise correlations between EC50 values of each DMI fungicide were positive and confirmed earlier indications of cross resistance.
David M. Gadoury - One of the best experts on this subject based on the ideXlab platform.
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Specific Isolation of RNA from the Grape Powdery Mildew Pathogen Erysiphe Necator, an Epiphytic, Obligate Parasite
Journal of Phytopathology, 2010Co-Authors: Lance Cadle-davidson, Robert C. Seem, Laura Wakefield, David M. GadouryAbstract:RNA expression profiling of obligately parasitic plant microbes is hampered by the requisite interaction of host and parasite. This can be especially problematic in the case of powdery mildews, such as Erysiphe Necator (syn. Uncinula Necator), which grow superficially but tightly adhere to the plant epidermis. We developed and refined a simple and efficient technique in which nail polish was used to remove conidia, appressoria, hyphae, conidiophores, and developing ascocarps of E. Necator from grapevine (Vitis vinifera) leaves and showed that RNA isolated after removal was not contaminated with V. vinifera RNA. This approach can be applied to expression analyses throughout fungal development and could be extended to other epiphytic pathogens and saprophytes.
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ontogenic resistance to Uncinula Necator varies by genotype and tissue type in a diverse collection of vitis spp
Plant Disease, 2008Co-Authors: Christopher T Gee, David M. Gadoury, Lance CadledavidsonAbstract:Berries of grapevine (Vitis spp.) have a limited window of susceptibility to Uncinula Necator, the causal agent of grapevine powdery mildew, until the onset of ontogenic resistance approximately 2 to 3 weeks postbloom. This phenomenon has been demonstrated in several cultivars of V. vinifera and in V. labruscana 'Concord', which all exhibited a similar duration of susceptibility. To identify genetic variation for ontogenic resistance, we screened a diverse collection of Vitis species and interspecific hybrids maintained in the USDA-ARS cold-hardy Vitis germplasm collection in Geneva, NY. Of the 79 genotypes whose fruit clusters were screened for susceptibility to powdery mildew under field conditions, 50 exhibited a high level of constitutive resistance to powdery mildew and did not develop more than trace levels of disease when inoculated, irrespective of the stage of berry development at inoculation. Twenty-four genotypes exhibited a significant gain of resistance as berries aged. This ontogenic resistance was conserved across four species and several interspecific hybrids of Vitis spp., although the timing of the onset of ontogenic resistance varied by genotype. The mechanism of ontogenic resistance was examined for four genotypes. Similar to previous studies, ontogenic resistance greatly reduced the incidence of successful penetration. Despite the broad conservation of ontogenic resistance across species, one genotype (V. rupestris 'R-65-44') remained susceptible past the onset of ripening, over 1 month later than reported previously for V. vinifera and V. labruscana. Variation in the resistance phenotype was observed among the rachis, pedicels, and berries within clusters of the majority of genotypes studied. The genetic variation in ontogenic resistance, in particular the discovery of a genotype in which berries remain susceptible as they mature, will facilitate further study of the inheritance and molecular basis of ontogenic resistance.
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effects of diffuse colonization of grape berries by Uncinula Necator on bunch rots berry microflora and juice and wine quality
Phytopathology, 2007Co-Authors: David M. Gadoury, Robert C. Seem, Wayne F Wilcox, Thomas Henickkling, Lorenza Conterno, Andrea Day, Andrea FickeAbstract:ABSTRACT Production of grape (principally cultivars of Vitis vinifera) for high-quality wines requires a high level of suppression of powdery mildew (Uncinula Necator syn. Erysiphe Necator). Severe infection of either fruit or foliage has well-documented and deleterious effects upon crop and wine quality. We found that berries nearly immune to infection by U. Necator due to the development of ontogenic resistance may still support diffuse and inconspicuous mildew colonies when inoculated ≈3 weeks post-bloom. Fruit with diffuse mildew colonies appear to be healthy and free of powdery mildew in late-season vineyard assessments with the naked eye. Nonetheless, presence of these colonies on berries was associated with (i) elevated populations of spoilage microorganisms; (ii) increased evolution of volatile ethyl acetate, acetic acid, and ethanol; (iii) increased infestation by insects known to be attracted to the aforementioned volatiles; (iv) increased rotting by Botrytis cinerea; and (v) increased frequency...
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Host Barriers and Responses to Uncinula Necator in Developing Grape Berries.
Phytopathology, 2004Co-Authors: Andrea Ficke, David M. Gadoury, Robert C. Seem, Dale Godfrey, Ian B. DryAbstract:ABSTRACT Grape berries are highly susceptible to powdery mildew 1 week after bloom but acquire ontogenic resistance 2 to 3 weeks later. We recently demonstrated that germinating conidia of the grape powdery mildew pathogen (Uncinula Necator) cease development before penetration of the cuticle on older resistant berries. The mechanism that halts U. Necator at that particular stage was not known. Several previous studies investigated potential host barriers or cell responses to powdery mildew in berries and leaves, but none included observation of the direct effect of these factors on pathogen development. We found that cuticle thickness increased with berry age, but that ingress by the pathogen halted before formation of a visible penetration pore. Cell wall thickness remained unchanged over the first 4 weeks after bloom, the time during which berries progressed from highly susceptible to nearly immune. Autofluorescent polyphenolic compounds accumulated at a higher frequency beneath appressoria on highly s...
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effects of ontogenic resistance upon establishment and growth of Uncinula Necator on grape berries
Phytopathology, 2003Co-Authors: Andrea Ficke, David M. Gadoury, Robert C. Seem, Ian B. DryAbstract:ABSTRACT Grape berries become resistant to powdery mildew early in development and are nearly immune to infection within 4 weeks after bloom. In this study, ontogenic resistance did not reduce attachment, germination, or appressorium formation of Uncinula Necator on 3- to 4-week-old berries of Vitis vinifera ‘Chardonnay’ or 3-week-old berries of V. labruscana ‘Concord’. Pathogen ingress halted at the cuticle before formation of a penetration pore. As berries aged, hyphal elongation and colony growth slowed until finally no secondary hyphae formed on fully resistant berries. More appressoria formed per unit of hyphal length as berries aged, indicating that failure to penetrate older berries led to increased attempts to penetrate resistant fruit. Additionally, hyphae within the colonies began to die as berries aged. Finally, the number of degree-hours between germination and sporulation of the colony (latent period) increased and sporophore density decreased with berry age at time of inoculation. Thus, onto...
H L Ypema - One of the best experts on this subject based on the ideXlab platform.
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the distribution of early season grapevine shoots infected by Uncinula Necator from year to year a case study in two california vineyards
American Journal of Enology and Viticulture, 2000Co-Authors: H L Ypema, W D GublerAbstract:Uncinula Necator (Schw.) Burr., the causal agent of powdery mildew on grapevines ( Vitis vinifera L.), survives the winter in the San Joaquin Valley in California predominantly by perennation in buds. Infected shoots arising from these buds (flag shoots) are important inoculum sources early in the growing season. Studies were conducted in two San Joaquin Valley vineyard sites over a three-year period to determine whether infected shoots tended to occur on the same vines from year to year. The studies also had the goal to determine whether the occurrence of infected shoots was influenced by the location of spurs retained from shoots infected the previous year. The number of vines with infected shoots in two consecutive years was greater than expected for a random infection process. The incidence of infected shoots arising from spurs retained from shoots infected the previous year was significantly greater than expected for a random shoot infection process. However, most infected shoots arose on spurs that were not infected the previous year, and they were not clustered around spurs retained from shoots infected the previous year. Removal of spurs retained from shoots infected the previous season during dormancy, or removal of flag shoots early in the season as a control measure by itself will probably not sufficiently reduce flag shoots incidence the following years
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long term effect of temperature and triadimefon on proliferation of Uncinula Necator implications for fungicide resistance and disease risk assessment
Plant Disease, 1997Co-Authors: H L Ypema, W D GublerAbstract:ABSTRACT Triadimefon has been used in California to control Uncinula Necator, causal agent of grape powdery mildew, since 1982. Instances of unsatisfactory control have occurred mainly in the cooler coastal areas of California. The effect of temperature and application of triadimefon was investigated over a 53-day-period on two U. Necator isolates, sensitive and resistant to triadimefon. At 15°C, 25°C, or temperatures fluctuating between 15 and 25°C, in absence of triadimefon, the isolates continued to produce high numbers of conidia for the entire duration of the experiment. Sporulation declined at daily maximum temperatures of 32°C for 6 h, 36°C for 3 h, and 40°C for 1 h, but was detectable when the experiment was terminated. At these temperature regimes, sporulation of the triadimefon-treated sensitive isolate ceased after 23 days. When treated with triadimefon, sporulation of the resistant isolate was comparable to that of the water-treated control. At daily maximum temperatures of 32°C for 11 h, 36°C...
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sensitivity of Uncinula Necator to benomyl triadimefon myclobutanil and fenarimol in california
Plant Disease, 1997Co-Authors: H L Ypema, M Ypema, W D GublerAbstract:ABSTRACT Sensitivity of Uncinula Necator subcultures to benomyl and the demethylation-inhibiting (DMI) fungicides triadimefon, myclobutanil, and fenarimol was assessed in 1993, 1994, and 1995 with leaf disk bioassays. In 1993, 1994, and 1995, 81.8, 96, and 96.7% of the subcultures, respectively, did not grow on leaf disks treated with 30 mg of benomyl per liter, whereas growth of the remaining subcultures was inhibited by more than 90%. Median EC50 values of triadimefon, myclobutanil, and fenarimol decreased from 1993 to 1994, and those of triadimefon decreased again from 1994 to 1995. In the same period, median EC50 values of all three DMI fungicides increased in a vineyard never exposed to DMI fungicides. The highest means and ranges of EC50 values found were those of triadimefon. Means and ranges were lower for myclobutanil and lowest for fenarimol, reflecting differences in inherent activities of the fungicides and po-tential for development of resistance. Pairwise correlations between EC50 values of ...
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sensitivity of Uncinula Necator to benomyl triadimefon myclobutanil and fenarimol in california
Plant Disease, 1997Co-Authors: H L Ypema, M Ypema, W D GublerAbstract:Sensitivity of Uncinula Necator subcultures to benomyl and the demethylation-inhibiting (DMI) fungicides triadimefon, myclobutanil, and fenarimol was assessed in 1993, 1994, and 1995 with leaf disk bioassays. In 1993, 1994, and 1995, 81.8, 96, and 96.7% of the subcultures, respectively, did not grow on leaf disks treated with 30 mg of benomyl per liter, whereas growth of the remaining subcultures was inhibited by more than 90%. Median EC50 values of triadimefon, myclobutanil, and fenarimol decreased from 1993 to 1994, and those of triadimefon decreased again from 1994 to 1995. In the same period, median EC50 values of all three DMI fungicides increased in a vineyard never exposed to DMI fungicides. The highest means and ranges of EC50 values found were those of triadimefon. Means and ranges were lower for myclobutanil and lowest for fenarimol, reflecting differences in inherent activities of the fungicides and po-tential for development of resistance. Pairwise correlations between EC50 values of each DMI fungicide were positive and confirmed earlier indications of cross resistance.
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occurrence of resistance in Uncinula Necator to triadimefon myclobutanil and fenarimol in california grapevines
Plant Disease, 1996Co-Authors: W D Gubler, H L Ypema, D G Ouimette, Larry J BettigaAbstract:Uncinula Necator subcultures from 19 vineyards in four regions in California were analyzed for sensitivity to triadimefon, myclobutanil, and fenarimol. The means of EC 50 values to triadimefon, myclobutanil, and fenarimol of U. Necator subcultures from a vineyard without previous exposure to demethylation inhibition (DMI) fungicides were 1.40, 0.15, and 0.13 mg/liter, respectively. The highest means of EC 50 values were found in the Central Coast region, and frequency distributions were skewed most toward higher resistance to all three fungicides. Subcultures with high resistance levels also were present in the other regions examined. A time course study performed in one vineyard, where resistant strains were reported, demonstrated a steady and significant increase in EC 50 values for all three fungicides during the growing season after multiple applications of triadimefon. Increased resistance to triadimefon, but not to myclobutanil and fenarimol, was maintained in early-formed ascospores released after the growing season.
Mariefrance Coriocostet - One of the best experts on this subject based on the ideXlab platform.
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nested allele specific pcr primers distinguish genetic groups of Uncinula Necator
Applied and Environmental Microbiology, 1999Co-Authors: Christophe Delye, Frederic Laigret, Valerie Ronchi, Mariefrance CoriocostetAbstract:Isolates of the obligately biotrophic fungus Uncinula Necator cluster in three distinct genetic groups (groups I, II, and III). We designed PCR primers specific for these groups in order to monitor field populations of U. Necator. We used the nucleotide sequences of the gene that encodes eburicol 14α-demethylase (CYP51) and of the ribosomal DNA internal transcribed spacer 1 (ITS1), ITS2, and 5.8S regions. We identified four point mutations (three in CYP51 and one in ITS1) that distinguished groups I and II from group III based on a sample of 132 single-spore isolates originating from Europe, Tunisia, Israel, India, and Australia. We developed a nested allele-specific PCR assay in which the CYP51 point mutations were used to detect and distinguish groups I and II from group III in crude mildewed samples from vineyards. In a preliminary study performed with samples from French vineyards in which isolates belonging to genetic groups I and III were present, we found that a shift from a population composed primarily of group I isolates to a population composed primarily of group III isolates occurred during the grapevine growing season.
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origin of primary infections of grape by Uncinula Necator rapd analysis discriminates two biotypes
Fungal Biology, 1998Co-Authors: Christophe Delye, Mariefrance CoriocostetAbstract:Thirty-one clonal isolates of U. necalor were taken from diseased grapes from three different vineyards in France and Germany. Samples were collected in April from typical ‘flagshoot’ symptoms, and in July and August from the same plants. The mating-type and the sensitivity to the fungicide triadimenol were determined for all isolates. Techniques for obtaining and characterizing isolates are described. Two isolates in the first sampling and eight in the second were resistant to triadimenol, with resistance factors ranging from 3·4 to 11·8. All isolates in the first sampling and nine out of the 21 isolates in the second were mating-type (+), the remaining isolates were mating-type (−). Genetic ariation between all isolates was assessed using the RAPD technique. Phenetic analysis based on the 364 RAPD fragments obtained revealed two very distinct groups, one group containing nine out of the 10 isolates from the first sampling, the second group containing all the remaining isolates. Isolates clustered in the first group displayed 58 RAPD fragments specific to them. These isolates did not exhibit 60 RAPD fragments present in all other isolates. Molecular and biological data suggested that isolates clustering in the two groups represent two different biotypes of U. Necator , which are likely to be genetically isolated.
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a mutation in the 14 alpha demethylase gene of Uncinula Necator that correlates with resistance to a sterol biosynthesis inhibitor
Applied and Environmental Microbiology, 1997Co-Authors: Christophe Delye, Frederic Laigret, Mariefrance CoriocostetAbstract:We investigated the molecular basis of resistance of the obligate biotrophic grape powdery mildew fungus Uncinula Necator to sterol demethylation-inhibiting fungicides (DMIs). The sensitivity of 91 single-spore field isolates of U. Necator to triadimenol was assessed by using a leaf disc assay. Resistance factors (RF) ranged from 1.8 to 26.0. The gene encoding the target of DMIs (eburicol 14 alpha-demethylase) from five sensitive and seven resistant isolates was cloned and sequenced. A single mutation, leading to the substitution of a phenylalanine residue for a tyrosine residue at position 136, was found in all isolates exhibiting an RF higher than 5. No mutation was found in sensitive or weakly resistant (RF, < 5) isolates. An allele-specific PCR assay was developed to detect the mutation. Among the 91 isolates tested, only isolates with RF higher than 5 carried the mutation. Three of the 19 resistant isolates and all sensitive and weakly resistant isolates did not possess the mutation. The mutation at codon 136 is thus clearly associated with high levels of resistance to triadimenol.
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rapd analysis provides insight into the biology and epidemiology of Uncinula Necator
Phytopathology, 1997Co-Authors: Christophe Delye, Frederic Laigret, Mariefrance CoriocostetAbstract:ABSTRACT Ninety isolates of grape powdery mildew (Uncinula Necator) from Europe (sixty-two) and India (twenty-eight) were collected. Ten of the sixty-two European isolates originated from mycelium overwintering in dormant buds (“flagshoots”). Mating types were determined, and genetic variation was assessed by random amplified polymorphic DNA (RAPD). Forty-one European isolates, including all “flagshoot” isolates, were mating type +, and twenty-one were mating type -. All Indian isolates were mating type -. Phenetic analysis based on 414 amplicons revealed three main groups. Most European isolates (53) clustered together. Nine flagshoot isolates clustered in a second distinct group. These isolates, which coexisted with other isolates in the field, may represent a genetically isolated biotype of U. Necator. Indian isolates clustered into two groups. The first group (15 isolates) was a subgroup of the group containing European nonflagshoot isolates. The second group (12 isolates) was distinct from the other ...
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a rapd assay for strain typing of the biotrophic grape powdery mildew fungus Uncinula Necator using dna extracted from the mycelium
Experimental Mycology, 1995Co-Authors: Christophe Delye, Mariefrance Coriocostet, Frederic LaigretAbstract:Abstract Delye, C., Corio-Costet, M.-F., and Laigret, F. 1995. A RAPD assay for strain typing of the biotrophic grape powdery mildew fungus Uncinula Necator using DNA extracted from the mycelium. Experimental Mycology 19, 234-237. We describe, for the first time, a RAPD assay using DNA extracted from the mycelium of a powdery mildew fungus, Uncinula Necator , a pathogen of grape. No contamination by plant DNA was observed, and the resulting patterns were fully repetitive. RAPD profiles were unchanged when using two different DNA polymerases or three different thermocyclers. Thirteen strains were tested for amplification, using 95 primers. Only 4% of the amplified fragments were polymorphic. Cluster analysis revealed that the strains from the same geographical origin had the higher genetic similarity, suggesting a short-range dissemination of U. Necator . This RAPD assay was also successfully applied to the grape downy mildew fungus, Plasmopara viticola , indicating that it can be used for other fungi which cannot be grown on artificial media.
