Orchard Factors Associated with Resistance and Cross Resistance to Sterol Demethylation Inhibitor Fungicides in Populations of <i>Venturia inaequalis</i> from Pennsylvania

Pfeufer, Emily E.; Ngugi, Henry K.

doi:10.1094/phyto-04-11-0117

Cited by 42 publications

(43 citation statements)

References 28 publications

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“…In contrast, V. inaequalis populations from the two commercial orchards exhibited frequencies of isolates with RG ≥70 of 39.4% and 63.6%, respectively. Similar results were obtained by Pfeufer and Ngugi (). These results suggest that RG values above 70% at the SAC of 0.05 mg a.i./l may be a suitable threshold for detection of V. inaequalis isolates that cause practical DMI field resistance.…”

Section: Discussionsupporting

confidence: 91%

Sensitivity of Venturia inaequalis to Trifloxystrobin and Difenoconazole in Uruguay

Mondino

Casanova

Bentancur

et al. 2014

Journal of Phytopathology

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The sensitivity of Venturia inaequalis to trifloxystrobin and difenoconazole was studied in Uruguay. Populations of V. inaequalis were collected from apple orchards with different histories of trifloxystrobin use. Sensitivity of populations to trifloxystrobin was analysed using a method for testing spore germination published by FRAC, using a discriminatory concentration of 2.0 mg a.i./l. Resistance to trifloxystrobin was widespread in the region of commercial apple production with resistance detected in all orchards examined, the incidences ranging from 3% to 95%. The highest frequencies were found in orchards with the most intensive use of Quinone outside inhibitors (Q o I) fungicides. Sensitivities of isolates of V. inaequalis to difenoconazole were assessed at five concentrations using a mycelial growth assay on isolates (33 isolates per orchard) from one non-commercial (baseline orchard) and two commercial orchards having differing histories of difenoconazole use. Populations in both commercial orchards exhibited reduced sensitivities to difenoconazole compared to the baseline orchard. Resistance factor (RF) values of 6.6 and 11.74 were measured in the orchards with moderate (up to 4 sprays per season) and intensive use (more than 5 sprays per season) of difenoconazole, respectively. A single-assessment concentration (SAC) was identified for assessing difenoconazole sensitivity of V. inaequalis isolates by fitting linear regressions between log 10 EC 50 and relative growth (RG) of the isolates at each fungicide concentration testing, and comparing the goodness-of-fit of the regression lines. Comparable results were obtained based on EC 50 values and RG values at a SAC of 0.05 mg of active ingredient per litre (a.i. per l). Populations from both commercial orchards differed from the baseline population, in that isolates with RG ≥70 were present at substantial levels in the former but absent from the latter.

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Section: Discussionsupporting

confidence: 91%

Sensitivity of Venturia inaequalis to Trifloxystrobin and Difenoconazole in Uruguay

Mondino

Casanova

Bentancur

et al. 2014

Journal of Phytopathology

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“…). Thus, localized populations of pathogens are repeatedly exposed to DMI fungicides over a period of years (Pfeufer and Ngugi ). In contrast, many growers crop fields to cucurbits every second or third year, which allows time for most crop debris carrying D. bryoniae to decompose (Keinath , ).…”

Section: Discussionmentioning

confidence: 99%

“…An increased risk of DMI insensitivity was observed with V. inaequalis , which is in the same taxonomic order as D. bryoniae , in orchards receiving more than four or five DMI applications per season (May‐De et al. ; Pfeufer and Ngugi ).…”

Section: Discussionmentioning

confidence: 99%

Isolates of Didymella bryoniae from South Carolina Remain Sensitive to DMI Fungicides Despite Multiyear Exposure

Keinath

Hansen

2012

Journal of Phytopathology

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Triazole fungicides, which are sterol demethylation inhibitors, have become the primary systemic fungicides applied to cucurbits to control gummy stem blight caused by Didymella bryoniae. Isolates of D. bryoniae from South Carolina that were never exposed to tebuconazole or exposed for several years were tested for sensitivity to tebuconazole and difenoconazole. Colony diameters, percentage germination of ascospores and conidia, and germ tube lengths were measured when isolates were grown on agar amended with 0.10–10.0 mg/l tebuconazole and 0.01–1.0 mg/l difenoconazole. All 147 isolates tested were sensitive to tebuconazole and difenoconazole with mean EC50 values of 0.41 and 0.054 mg/l, respectively. Ascospore germination was greater than conidia germination on fungicide‐amended agar. Although the length of germ tubes arising from both spore types was reduced by both fungicides, the reduction was greater for ascospore germ tubes than for conidia germ tubes. Because many watermelon growers rotate crops among fields every two years, local populations of D. bryoniae have not been exposed repeatedly to tebuconazole. In addition, growers often apply a rotation of systemic and contact fungicides. Thus, despite exposure to tebuconazole for up to nine years, isolates of D. bryoniae from South Carolina remain sensitive to triazole fungicides.

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“…As discussed by Klix et al (2007), the decline in the sensitivity to triazoles of F. graminearum owing to selection is not generally considered a key determinant of the relatively low fungicide efficacy against FHB under field conditions. However, it is well known from the literature that failures in disease control have been associated with the decline in sensitivity of other important pathogens such as Monilinia fructicola (Chen et al, 2012), Venturia inaequalis (Pfeufer & Ngugi, 2012) and Mycosphaerella graminicola (Leroux et al, 2007) due to indiscriminate use of triazoles.…”

mentioning

confidence: 99%

“…Cumulative frequency plots of the EC 50 were produced and the median and mean values were calculated for each fungicide (Pfeufer & Ngugi, 2012). The isolates were split into two groups of ten isolates.…”

mentioning

confidence: 99%

Sensitivity of Fusarium graminearum causing head blight of wheat in Brazil to tebuconazole and metconazole fungicides

Spolti

Jorge

Ponte

2012

Trop. plant pathol.

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Fusarium head blight (FHB) of wheat, is caused by fungal populations belonging to the Fusarium graminearum species complex. Although triazole fungicides are widely used in FHB management, information about the sensitivity of F. graminearum populations to such fungicides is scarce, particularly in Brazil. This work aimed at determining the sensitivity of pathogenic populations of F. graminearum to metconazole and tebuconazole. Fungal isolates were obtained from diseased wheat heads collected in commercial fields at the northern region of Rio Grande do Sul state, Brazil, along the 2009 and 2010 growing seasons. Fifty isolates obtained from eleven locations were grown in media amended with increasing fungicide dosages and the effective concentration reducing mycelial growth to 50% (EC 50 ) was determined. The median of the EC 50 values was 0.001 mg/L (<0.001-0.152 mg/L) and 0.037 mg/L (<0.001-0.324), for tebuconazole and metconazole, respectively. Cross-resistance was detected based on significance of correlation analysis (r s = 0.46; P < 0.0001) between the log-transformed EC 50 of the two triazoles. The mean EC 50 for a group of ten isolates classified as "more sensitive" differed statistically from the ten isolates representing the "less sensitive" group. Nevertheless, these groups did not differ in terms of mycelial growth on PDA in the absence of fungicides. It was concluded that pathogenic populations of F. graminearum are sensitive to the triazoles at various levels due to the intrinsic characteristics of the isolates or to selection pressure by the increasing fungicide use.

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

Cited by 42 publications

References 28 publications

Sensitivity of Venturia inaequalis to Trifloxystrobin and Difenoconazole in Uruguay

Sensitivity of Venturia inaequalis to Trifloxystrobin and Difenoconazole in Uruguay

Isolates of Didymella bryoniae from South Carolina Remain Sensitive to DMI Fungicides Despite Multiyear Exposure

Sensitivity of Fusarium graminearum causing head blight of wheat in Brazil to tebuconazole and metconazole fungicides

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