scholarly journals Distributions of Sensitivities to Three Sterol Demethylation Inhibitor Fungicides Among Populations of Uncinula necator Sensitive and Resistant to Triadimefon

1997 ◽  
Vol 87 (8) ◽  
pp. 784-791 ◽  
Author(s):  
Eugene O. Erickson ◽  
Wayne F. Wilcox
Keyword(s):  
Powdery Mildew ◽  
Active Form ◽  
Correlation Coefficients ◽  
The Other ◽  
Cross Resistance ◽  
Uncinula Necator ◽  
Previous Exposure ◽  
Grapevine Powdery Mildew ◽  
Dmi Fungicides ◽  
Demethylation Inhibitor

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 (ED50 values exceeding 0.56, 0.18, and 0.18 μg/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 ED50 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.

scholarly journals Sensitivity of grapevine powdery mildew (Erysiphe necator) to demethylation inhibitor and quinone outside inhibitor fungicides in New Zealand

2016 ◽  
Vol 69 ◽  
pp. 1-10 ◽  
Author(s):  
R.M. Beresford ◽  
P.J. Wright ◽  
P.N. Wood ◽  
R.H. Agnew
Keyword(s):  
Fungicide Resistance ◽  
Strong Relationship ◽  
The Other ◽  
Erysiphe Necator ◽  
Colony Diameter ◽  
Quinone Outside Inhibitor ◽  
Grapevine Powdery Mildew ◽  
Dmi Fungicides ◽  
Grape Leaf ◽  
Demethylation Inhibitor

Isolates of Erysiphe necator from Hawkes Bay and Marlborough vineyards were tested for sensitivity to three demethylation inhibitor (DMI) fungicides (myclobutanil penconazole and cyproconazole) and one quinone outside inhibitor (QoI) fungicide (trifloxystrobin) Mean colony diameter was determined in a detached grape leaf assay for approximately 20 isolates per vineyard at 1 and 10 mg/litre of each fungicide Resistance to trifloxystrobin was prevalent in Hawkes Bay and Marlborough Mycobutanil resistance was found in both regions but particularly in Marlborough There was some loss of sensitivity to penconazole particularly in Marlborough Cyproconazole showed greater efficacy against E necator than the other two DMIs tested There was no explanation for the high trifloxystrobin resistance in sampled vineyards with few reports of trifloxystrobin use For DMIs there was a strong relationship between number of DMI fungicide applications over 10 years and DMI resistance across all three DMI active ingredients in both regions

scholarly journals Sensitivity of Uncinula necator to Benomyl, Triadimefon, Myclobutanil, and Fenarimol in California

Plant Disease ◽  
1997 ◽  
Vol 81 (3) ◽  
pp. 293-297 ◽  
Author(s):  
H. L. Ypema ◽  
M. Ypema ◽  
W. D. Gubler
Keyword(s):  
Leaf Disk ◽  
Cross Resistance ◽  
Uncinula Necator ◽  
Development Of Resistance ◽  
Pairwise Correlations ◽  
Dmi Fungicides ◽  
Leaf Disks

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.

Release, germination, and pathogenicity of ascospores of Uncinula necator under controlled conditions

1998 ◽  
Vol 76 (5) ◽  
pp. 777-781 ◽  
Author(s):  
F Jailloux ◽  
T Thind ◽  
M Clerjeau
Keyword(s):  
Powdery Mildew ◽  
Vitis Vinifera ◽  
Storage Conditions ◽  
Vitis Vinifera L ◽  
Uncinula Necator ◽  
Grapevine Powdery Mildew ◽  
Germination Ability ◽  
Ascospore Release ◽  
Probable Role ◽  
Leaf Disks

A laboratory technique was standardized for studying the release, maturation, germination, and pathogenicity of ascospores of Uncinula necator (Schw.) Burr. Surface disinfestation and wetting of grape (Vitis vinifera L.) leaf disks bearing cleistothecia collected in the vineyard before incubation in a humid chamber for 48 h at 20°C were found essential for obtaining the release of ascospores (8 ascospores/cm2). Storage conditions involving periodic wetting treatments of cleistothecia at 5°C during 110 days were necessary to induce both ascospore release (80 ascospores/cm2) and germination ability (62%). The matured ascospores were pathogenic on healthy leaf disks at 20°C indicating their probable role as a primary inoculum source. This technique can be helpful in studying the inheritance of characteristics such as pathogenicity and fungicidal resistance.Key words: cleistothecia, ascospores, maturation, germination, pathogenicity, Uncinula necator, grapevine, powdery mildew.

scholarly journals Analysis of mutations in West Australian populations ofBlumeria graminisf. sp.hordei CYP51conferring resistance to DMI fungicides

2019 ◽  
Author(s):  
M. A. Tucker ◽  
F. Lopez-Ruiz ◽  
H. J. Cools ◽  
J. G. L. Mullins ◽  
K. Jayasena ◽  
...  
Keyword(s):  
Powdery Mildew ◽  
Target Gene ◽  
Docking Studies ◽  
Protein Docking ◽  
Yeast Strains ◽  
Barley Powdery Mildew ◽  
Dmi Fungicides ◽  
Altered Sensitivity ◽  
Resistant Genotypes ◽  
Demethylation Inhibitor

SummaryPowdery mildew caused byBlumeria graminisf. sp.hordei(Bgh) is a constant threat to barley production but is generally well controlled through combinations of host genetics and fungicides. An epidemic of barley powdery mildew was observed from 2007 to 2013 in the West Australian wheatbelt (WA). We collected isolates, examined their sensitivity to demethylation inhibitor (DMI) fungicides and sequenced the Cyp51B target gene. Five amino acid substitutions were found of which four were novel. A clear association was established between combinations of mutations and altered levels of resistance to DMIs. The most resistant genotypes increased in prevalence from 0 in 2009 to 16% in 2010 and 90% in 2011. Yeast strains expressing theBghCyp51 genotypes replicated the altered sensitivity to various DMIs and these results were confirmed byin silicoprotein docking studies.

scholarly journals Orchard Factors Associated with Resistance and Cross Resistance to Sterol Demethylation Inhibitor Fungicides in Populations of Venturia inaequalis from Pennsylvania

2012 ◽  
Vol 102 (3) ◽  
pp. 272-282 ◽  
Author(s):  
Emily E. Pfeufer ◽  
Henry K. Ngugi
Keyword(s):  
Odds Ratio ◽  
Management Practices ◽  
Venturia Inaequalis ◽  
Cross Resistance ◽  
Single Spore ◽  
Quantitative Evidence ◽  
Development Of Resistance ◽  
Orchard Management ◽  
Dmi Fungicides ◽  
Demethylation Inhibitor

Orchard management practices, such as destroying of overwintered inoculum and limiting the number of fungicide applications, are often recommended as tactics for slowing the development of resistance to sterol demethylation-inhibitor (DMI) fungicides in populations of Venturia inaequalis. However, there is little quantitative evidence relating the use of such practices to levels of resistance in orchards. The aim of this study was to evaluate the sensitivity of V. inaequalis isolates from Pennsylvania to DMI fungicides, and to identify orchard management factors related to the incidence of resistant isolates. In total, 644 single-spore V. inaequalis cultures obtained from 20 apple orchards in 2008 or 2009 were tested for sensitivity to myclobutanil, fenbuconazole, or difenoconazole. Growers provided management history of the sampled plots. Widespread shifts toward resistance to the three fungicides were noted, with mean effective concentration for 50% inhibition (EC50) values of 2.136, 0.786, and 0.187 μg/ml for myclobutanil, fenbuconazole, and difenoconazole, respectively. Cross resistance to the three fungicides was documented in high correlation (Spearman's r > 0.6) between mean EC50 values for 14 orchards. Based on a 0.5-μg/ml threshold, 66 and 26% of isolates were resistant to myclobutanil and fenbuconazole, respectively, and 22% were cross resistant to the two fungicides. A significant between-year shift toward increased resistance was noted in two of three orchards surveyed in both years. Failure to use dormant copper sprays, older trees, larger orchards, orchards with ≤10 cultivars, and application of >4 DMI sprays were positively correlated (0.0001 < P < 0.05) with the incidence of resistant isolates. Isolates from orchards with >4 DMI sprays were four times as likely to be resistant to fenbuconazole (odds ratio = 4.57; P = 0.015). Isolates from orchards without dormant copper sprays were twice as likely to be cross-shifted toward resistance to all three fungicides (odds ratio = 1.76; P = 0.048). Results identify management practices that can reduce the risk of V. inaequalis developing resistance to DMI fungicides.

scholarly journals Suppression of Grapevine Powdery Mildew by a Mycophagous Mite

Plant Disease ◽  
2005 ◽  
Vol 89 (12) ◽  
pp. 1331-1338 ◽  
Author(s):  
Heather S. Melidossian ◽  
Robert C. Seem ◽  
Greg English-Loeb ◽  
Wayne F. Wilcox ◽  
David M. Gadoury
Keyword(s):  
Powdery Mildew ◽  
Vitis Vinifera ◽  
Uncinula Necator ◽  
Laboratory Studies ◽  
Rapid Loss ◽  
Infection Efficiency ◽  
Grapevine Powdery Mildew ◽  
Grape Powdery Mildew

Orthotydeus lambi reduced the severity of grape powdery mildew (Uncinula necator) on fruit and foliage of Vitis vinifera ‘Chardonnay’ and ‘Riesling’ in repeated field and laboratory trials. Vines were infested with O. lambi at two densities (5 or 30 mites per leaf) at each of two times (2 to 3 weeks prebloom and 1 week postbloom). Overall, powdery mildew on the berries and foliage was suppressed by early (prebloom) mite releases at both densities, but only by the higher density in late (postbloom) releases. In a separate trial, when foliage was infested at 30 mites per leaf but mites were excluded from certain fruit clusters, severity of powdery mildew was significantly reduced on the mite-free clusters of mite-infested shoots. Thus, O. lambi may suppress powdery mildew on the fruit by reducing inoculum from foliar infections. In laboratory studies, both immature and mature mites reduced infection efficiency, colony expansion, and sporulation of the mildew colonies; but immature mites were more voracious feeders, consuming more pathogen biomass per unit of mite biomass. Mites tore at the mycelium and conidia with their palps during feeding, leading to leakage, rapid loss of hyphal turgor, and collapse of hyphae.

scholarly journals Sensitivity of California Isolates of Uncinula necator to Trifloxystrobin and Spiroxamine, and Update on Triadimefon Sensitivity

Plant Disease ◽  
2004 ◽  
Vol 88 (11) ◽  
pp. 1205-1212 ◽  
Author(s):  
T. C. Miller ◽  
W. D. Gubler
Keyword(s):  
Regional Scale ◽  
Mean Value ◽  
Uncinula Necator ◽  
Single Spore ◽  
Sample Mean ◽  
Frequency Distributions ◽  
Development Of Resistance ◽  
Dmi Fungicides ◽  
Median Effective Concentration ◽  
Demethylation Inhibitor

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 a 5.3 to 14.5 mg/liter 95% CI, and those values were significantly higher than those obtained in the last assay 12 years earlier. Significant differences in sensitivity of U. necator to triadimefon were detected at a regional scale by comparison of mean EC50 values of frequency distributions representative of regions within California, although the relations between those regions were different from the prior survey.

scholarly journals Sensitivity of the U.S. Blumeria graminis f. sp. tritici Population to Demethylation Inhibitor Fungicides

Plant Disease ◽  
2019 ◽  
Vol 103 (12) ◽  
pp. 3108-3116 ◽  
Author(s):  
Emily Meyers ◽  
Consuelo Arellano ◽  
Christina Cowger
Keyword(s):  
United States ◽  
Population Level ◽  
The United States ◽  
Blumeria Graminis ◽  
Cross Resistance ◽  
Eastern United States ◽  
Fungicide Sensitivity ◽  
Dmi Fungicides ◽  
The U.S ◽  
Demethylation Inhibitor

Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici, is managed in the United States with cultivar resistance and foliar fungicides. Despite high levels of fungicide sensitivity in other cereal mildew populations, fungicide sensitivity of U.S. B. graminis f. sp. tritici has never been evaluated. Almost 400 B. graminis f. sp. tritici isolates were collected from 15 U.S. states over 2 years and phenotyped for sensitivity to two widely used demethylation inhibitor (DMI) fungicides, tebuconazole and prothioconazole. A large range of sensitivity to both DMIs was observed, with more insensitive isolates originating from the eastern United States (Great Lakes, Mid-Atlantic, and Southeast regions) and more sensitive isolates from central states (Plains region, Arkansas, and Missouri). Cross-resistance was indicated by a positive although weak association between tebuconazole and prothioconazole sensitivities at all levels of analysis (EC50 values, P < 0.0001). A possible fitness cost was also associated with prothioconazole insensitivity (P = 0.0307) when analyzed at the state population level. This is the first assessment of fungicide sensitivity in the U.S. B. graminis f. sp. tritici population, and it produced evidence of regional selection for reduced DMI efficacy. The observation of reduced sensitivity to DMI fungicides in the eastern United States underlines the importance of rotating between chemistry classes to maintain the effectiveness of DMIs in U.S. wheat production. Although cross-resistance was demonstrated, variability in the relationship of EC50 values for tebuconazole and prothioconazole also suggests that multiple mechanisms influence B. graminis f. sp. tritici isolate responses to these two DMI fungicides.

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