Sensitivity Distribution ofVenturia inaequalisto the Sterol Demethylation Inhibitor Flusilazole: Baseline Sensitivity and Implications for Resistance Monitoring

This study was initiated to quantify the baseline sensitivity of apple scab (Venturia inaequalis) to fenarimol, an ergosterol synthesis-inhibiting fungicide. In 1988, 576 monoconidial isolates of Venturia inaequalis were collected from 26 commercial orchards throughout Quebec. Sensitivity to fenarimol was assessed by radial growth inhibition assay. The ED50 values for the 26 orchards ranged from 0.024 to 5.212 (μ g mL-1 with a mean ED50 of 0.156 μg ml-1. Reduced sensitivity, expressed as ED50, was found in three orchards for an overall frequency of 4.51% of isolates. Sensitive isolates had a mean ED50 of 0.079 μg ml-1, whereas isolates with reduced sensitivity had a mean ED50 of 1.714 μ g mL-1, yielding a resistance factor of about 22. Four populations were identified based on the frequency distribution of ED50 values.

Download Full-text

Baseline Sensitivity and Toxic Action of the Sterol Demethylation Inhibitor Flusilazole Against Botrytis cinerea

Plant Disease ◽

10.1094/pdis-11-19-2478-re ◽

2020 ◽

Vol 104 (11) ◽

pp. 2986-2993

Author(s):

Yong Wang ◽

Miaomaio Wang ◽

Letian Xu ◽

Yang Sun ◽

Juntao Feng

Keyword(s):

Botrytis Cinerea ◽

Plant Pathogens ◽

Resistance Mechanism ◽

Point Mutations ◽

Gray Mold ◽

Shaanxi Province ◽

Cross Resistance ◽

Baseline Sensitivity ◽

Single Spore ◽

Demethylation Inhibitor

In the present study, a total of 95 Botrytis cinerea single-spore strains collected from different hosts in Shaanxi Province of China were characterized for their sensitivity to the sterol demethylation inhibitor fungicide flusilazole. The effective concentration for 50% inhibition of mycelial growth (EC50) of flusilazole ranged from 0.021 to 0.372 µg/ml, with an average value of 0.093 µg/ml. Cross-resistance between flusilazole and commonly used fungicides was not detected, and no flusilazole-resistant mutants were induced. Both on detached strawberry leaves and in greenhouse experiments, flusilazole was more effective than the commonly used fungicide carbendazim at reducing gray mold. After culture on PDA plates or detached strawberry leaves, no difference in sclerotia production or pathogenicity was detected between two strains, WG12 (most sensitive to flusilazole) and MX18 (least sensitive to flusilazole). After treatment with flusilazole, however, the two strains lost the ability to produce sclerotia, and oxalic acid and ergosterol contents in mycelium decreased. Interestingly, the inhibition rate of ergosterol content in MX18 was significantly lower than that in WG12. Expression of Cyp51, BcatrD, and Bcmfs1 genes all increased after treatment with flusilazole, especially the Cyp51 and BcatrD genes. However, the expression of Cyp51 gene or BcatrD gene in WG12 and MX18 were significantly different from each other after treatment with flusilazole. In addition, no point mutations in Cyp51 gene were found in MX18. These data suggest flusilazole is a promising fungicide for resistance management of gray mold and also provided novel insights into understanding the resistance mechanism of flusilazole against plant pathogens.

Download Full-text

Sensitivity to Azoxystrobin Among Isolates of Uncinula necator: Baseline Distribution and Relationship to Myclobutanil Sensitivity

Plant Disease ◽

10.1094/pdis.2002.86.4.394 ◽

2002 ◽

Vol 86 (4) ◽

pp. 394-404 ◽

Cited By ~ 68

Author(s):

Francis P. Wong ◽

Wayne F. Wilcox

Keyword(s):

New York ◽

High Sensitivity ◽

Intrinsic Activity ◽

Uncinula Necator ◽

In Planta ◽

Baseline Sensitivity ◽

Sensitivity Distribution ◽

Resistant Population ◽

History Of ◽

Low Sensitivity

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.

Download Full-text

Characterization of baseline sensitivity and resistance risk of Colletotrichum gloeosporioides complex isolates from strawberry and grape to two demethylation-inhibitor fungicides, prochloraz and tebuconazole

Australasian Plant Pathology ◽

10.1007/s13313-014-0321-8 ◽

2014 ◽

Vol 43 (6) ◽

pp. 605-613 ◽

Cited By ~ 19

Author(s):

X. F. Xu ◽

T. Lin ◽

S. K. Yuan ◽

D. J. Dai ◽

H. J. Shi ◽

...

Keyword(s):

Colletotrichum Gloeosporioides ◽

Baseline Sensitivity ◽

Resistance Risk ◽

Colletotrichum Gloeosporioides Complex ◽

Demethylation Inhibitor

Download Full-text

Detection and Characterization of Benzimidazole Resistance in California Populations of Colletotrichum cereale

Plant Disease ◽

10.1094/pdis-92-2-0239 ◽

2008 ◽

Vol 92 (2) ◽

pp. 239-246 ◽

Cited By ~ 31

Author(s):

Francis P. Wong ◽

Karla A. de la Cerda ◽

Rufina Hernandez-Martinez ◽

Sharon L. Midland

Keyword(s):

Creeping Bentgrass ◽

Baseline Sensitivity ◽

Putting Greens ◽

Thiophanate Methyl ◽

Annual Bluegrass ◽

Sensitivity Distribution ◽

Exposed Population ◽

Colletotrichum Cereale

Colletotrichum cereale is the causal agent of turfgrass anthracnose, which has become a serious problem on annual bluegrass (Poa annua) and creeping bentgrass (Agrostis palustris) golf course putting greens. Thiophanate-methyl is a benzimidazole (methyl benzimidazole carbamate [MBC]) fungicide used for the management of anthracnose. In this study, we examined 481 isolates from 10 California populations to determine the presence and frequency of MBC resistance. An in vitro methodology was developed to construct a baseline sensitivity distribution using 60 isolates from an unexposed population (TCGC). The 50% effective dose (ED50) values for the baseline sensitivity distribution for thiophanate-methyl ranged from 0.14 to 2.3 μg/ml with a mean of 0.75 μg/ml. For 60 isolates assayed from an exposed population (AHCC), 57 isolates were not responsive to in vitro concentrations of thiophanate-methyl of up to 30 μg/ml. Isolates nonresponsive to thiophanate-methyl were not responsive to benomyl in vitro. Two isolates nonresponsive in vitro to thiophanate-methyl or benomyl were not controlled in vivo on annual bluegrass plants treated preventively with either fungicide at 11 mg/ml, confirming the results of the in vitro testing. The remaining 361 isolates from eight populations were tested using the single discriminatory dose of thiophanate-methyl at 10 μg/ml. A high proportion (>90%) of isolates from six of the populations were resistant to thiophanate-methyl, indicating the presence of practical resistance at these locations. To determine the molecular mechanism of MBC resistance, the two β-tubulin genes, TUB1 and TUB2, of 12 resistant and 6 sensitive isolates were amplified and sequenced, revealing a glutamic acid to lysine substitution at position 198 of TUB2 that was present in all resistant isolates. This work confirms the presence of MBC resistance in C. cereale populations from California and presents methods and information that can be used to manage resistance to the MBC fungicides and improve anthracnose management programs.

Download Full-text

Baseline sensitivity and action mechanism of the sterol demethylation inhibitor flusilazole to Valsa mali

Pesticide Biochemistry and Physiology ◽

10.1016/j.pestbp.2020.104722 ◽

2021 ◽

Vol 171 ◽

pp. 104722

Author(s):

Yong Wang ◽

Lin Jiang ◽

Miao-Miao Wang ◽

Jun-Tao Feng

Keyword(s):

Action Mechanism ◽

Baseline Sensitivity ◽

Valsa Mali ◽

Demethylation Inhibitor

Download Full-text

Resistance of Venturia inaequalis to demethylation inhibitor and dodine fungicides in four New Zealand applegrowing regions

New Zealand Plant Protection ◽

10.30843/nzpp.2013.66.5654 ◽

2013 ◽

Vol 66 ◽

pp. 274-283 ◽

Cited By ~ 2

Author(s):

R.M. Beresford ◽

P.J. Wright ◽

P.N. Wood ◽

N.M. Park ◽

N.J. Larsen ◽

...

Keyword(s):

Venturia Inaequalis ◽

Agar Plate ◽

Black Spot ◽

Baseline Sensitivity ◽

Highly Sensitive ◽

Dmi Fungicides ◽

Inoculation Assay ◽

Plant Inoculation ◽

Demethylation Inhibitor ◽

Test Control

A survey of 41 apple orchards in Hawkes Bay (25) Nelson (7) Otago (4) and Waikato (5) provided 796 isolates of Venturia inaequalis (black spot or scab) which were tested using an agar plate assay for sensitivity to two demethylation inhibitor (DMI) fungicides (myclobutanil and penconazole) and to dodine Each fungicide was used at two concentrations to distinguish between highly sensitive sensitive and resistant isolates Sensitivity to DMIs in all regions was lower than baseline sensitivity in previous studies particularly for myclobutanil Waikato showed significantly lower DMI sensitivity than other regions Dodine sensitivity was greater than in the 1990s although Otago isolates were significantly less dodinesensitive than those from other regions In a plant inoculation assay to test control by five DMI fungicides of disease caused by resistant isolates flusilazol and difenoconazole gave significantly better disease control of resistant isolates than myclobutanil penconazole or fenbuconazole at standard field rates

Download Full-text

Incidence of Myclobutanil- and Kresoxim-Methyl-Insensitive Isolates of Venturia inaequalis in Quebec Orchards

Plant Disease ◽

10.1094/pdis-91-10-1351 ◽

2007 ◽

Vol 91 (10) ◽

pp. 1351-1358 ◽

Cited By ~ 15

Author(s):

T. Jobin ◽

O. Carisse

Keyword(s):

Lognormal Distribution ◽

Alternative Oxidase ◽

Venturia Inaequalis ◽

In Vitro Tests ◽

Baseline Sensitivity ◽

Scab Control ◽

The Mean ◽

High Level ◽

Demethylation Inhibitor

Sensitivity of baseline and exposed populations of Venturia inaequalis to myclobutanil and to kresoxim-methyl were evaluated in vitro. For myclobutanil, the population was constructed with 238 monoconidial isolates of V. inaequalis collected from 48 orchards. For kresoxim-methyl, the population was constructed with 251 monoconidial isolates collected from 49 orchards. Baseline populations were constructed with 34 and 29 monoconidial isolates collected from apple trees that had never been treated for myclobutanil and kresoxim-methyl, respectively. Sensitivity to fungicides was evaluated based on 50% effective dose (ED50) values. The V. inaequalis population that was not exposed to myclobutanil had a baseline sensitivity (mean ED50) of 0.064 μg/ml and showed a lognormal distribution. The V. inaequalis population constructed with isolates from commercial orchards had a mean ED50 of 2.600 μg/ml, which was significantly higher than the baseline sensitivity. The distribution of ED50 values did not follow a lognormal distribution. In response to declining levels of scab control with myclobutanil and other sterol demethylation inhibitor fungicides (DMIs), three orchards were more deeply investigated. The mean ED50 values were 1.618 (n = 23), 3.079 (n = 29), and 1.500 μg/ml (n = 20) in orchards one, two, and three, respectively. Resistant isolates, according to criteria set by other studies, accounted for 39, 76, and 85% of the isolates tested. The V. inaequalis population that had never been exposed to kresoxim-methyl had a baseline sensitivity (mean ED50) of 0.092 μg/ml and showed a lognormal distribution. The V. inaequalis population constructed with isolates from commercial orchards had a mean ED50 of 6.093 μg/ml, which was significantly higher than the baseline sensitivity. The distribution of ED50 values followed a lognormal distribution. However, when a subsample of isolates was retested for their sensitivity to kresoxim-methyl with the addition of salicylhydroxamic acid (an inhibitor of alternative oxidase) at 100 μg/ml to the growth medium, more than 98% inhibition was observed for all isolates. The results from in vitro tests showed a high level of resistance to myclobutanil and a low level of resistance to kresoxim-methyl, suggesting that the use of myclobutanil and DMIs should be discontinued or significantly reduced before practical resistance is reached.

Download Full-text