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

Plant Disease ◽  
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.

Difenoconazole Resistance Shift in Botrytis cinerea From Tomato in China Associated With Inducible Expression of CYP51

Plant Disease ◽  
2020 ◽  
pp. PDIS-03-20-0508
Author(s):  
Can Zhang ◽  
Muhammad Imran ◽  
Lu Xiao ◽  
Zhihong Hu ◽  
Guixiang Li ◽  
...  
Keyword(s):  
Botrytis Cinerea ◽  
Fungicide Resistance ◽  
Point Mutations ◽  
Gray Mold ◽  
Resistant Isolate ◽  
Upstream Region ◽  
Cross Resistance ◽  
Baseline Sensitivity ◽  
History Of ◽  
Nonnormal Distribution

Gray mold caused by Botrytis cinerea is one of the most important diseases in tomato. It can be controlled effectively by demethylation inhibitor (DMI) fungicides, but their resistance status after long-term use in the field is unclear. The baseline sensitivity to difenoconazole of 142 B. cinerea isolates from China with no history of DMI usage was characterized, with a mean effective concentration for 50% mycelial growth inhibition (EC50) of 0.97 ± 0.50 μg/ml. EC50 values for difenoconazole sensitivity of another 248 isolates collected in 2011 and 2016 ranged from 0.04 to 11.99 μg/ml, and the frequency of difenoconazole sensitivity formed a nonnormal distribution curve. Detached fruit studies revealed that isolates with EC50 values of approximately 6.00 μg/ml were not controlled effectively. The mean EC50 of the resistant isolates changed from 6.74 to 8.65 μg/ml between 2011 and 2016. Positive cross-resistance was only observed between difenoconazole and two DMIs. One dual resistant isolate and one triple resistant isolate were found among the difenoconazole-resistant isolates collected in 2016, associated with point mutations in corresponding target proteins of the fungicides azoxystrobin and fludioxonil. This indicated that B. cinerea not only showed higher difenoconazole resistance levels but gradually changed from single to multiple fungicide resistance over time. No amino acid variation was found in the CYP51 protein. In the absence of difenoconazole, the relative expression of CYP51 was not significantly different in sensitive and resistant isolates. Induced expression of CYP51 is an important determinant of DMI resistance in B. cinerea from tomato. However, nucleotide variants found in the upstream region had no association with the fungicide resistance phenotype. These results will be helpful for the management of B. cinerea in the field.

scholarly journals First Report of Iprodione Resistance in Botrytis cinerea on Blackberry from South Carolina

Plant Disease ◽  
2011 ◽  
Vol 95 (11) ◽  
pp. 1481-1481
Author(s):  
F. P. Chen ◽  
X. L. Liu ◽  
X. P. Li ◽  
G. Schnabel
Keyword(s):  
South Carolina ◽  
Botrytis Cinerea ◽  
Disease Incidence ◽  
Gray Mold ◽  
Resistant Isolate ◽  
Cross Resistance ◽  
Broad Host Range ◽  
Paper Strip ◽  
Single Spore ◽  
First Report

Botrytis cinerea Pers.:Fr., is a necrotrophic fungus with a broad host range that causes gray mold on hundreds of plant species (2). Control of gray mold mainly depends on fungicides, including the dicarboxamide iprodione. Thirty-nine diseased blackberry fruit were collected from four orchards in South Carolina and the sensitivity of single-spore isolates to iprodione was examined by Spiral Plater assays (1) on potato dextrose agar (PDA). Briefly, a 5.3 cm long paper strip containing mycelia was placed along the concentration gradient of the PDA and 50% inhibition (EC50 value) was calculated after 2 days of incubation with the Spiral Gradient Endpoint (SGE) software (Spiral Biotech, Norwood, MA). Each isolate was tested in duplicates. Sensitivity ranged from 0.043 to 2.596 μg/ml, with a maximum resistance factor of 60.4. Isolates with EC50 values greater than 2 μg/ml were found in two orchards. Those isolates represented 40 and 7.1% of the total isolates from each orchard. Two isolates with high (EC50 value of 2.596 μg/ml) and low (EC50 value of 0.062 μg/ml) values were chosen to determine the efficacy of iprodione formulated product Rovral 4 Fl (Bayer CropSciences, Research Triangle Park, NC) on detached apple fruit. Fifteen apples were used for each isolate and experiment. Each fruit was wounded on the surface in three locations with a sterile syringe and inoculated with 15 μl of a spore suspension (106 conidia/ml) at the wounded sites. Rovral was applied at the recommended label rate either 24 h before (protective treatment) or 48 h after inoculation (curative treatment). The experiment was conducted three times. Blackberry fruit were not found suitable for this assay because of persistent contamination problems likely from latent infections of a symptomatic fruit. Disease incidence and lesion diameter were recorded 7 days after incubation. Disease incidence following inoculation of the sensitive and resistant isolates on non-fungicide-treated fruit was 100 and 86.7%, respectively. Disease incidence on fungicide-treated apples was 4.4% for the sensitive isolate and 75.6% for the resistant isolate with corresponding mean lesion areas of 0.36 mm and 9.37 mm, respectively. Both isolates were controlled effectively in protective treatments, however, indicating low levels of resistance. To our knowledge, this is the first report of iprodione resistance in B. cinerea from blackberry or any other field-grown crop in South Carolina. This finding adds to a study from 1999 (3) documenting resistance to the dicarboxamide fungicide vinclozolin in B. cinerea collected from ornamentals in South Carolinian greenhouses and suggests that resistance to iprodione needs to be considered in the design of gray mold control strategies in commercial blackberry orchards. No cross resistance between the phenylpyrrole fludioxonil and iprodione was found. References: (1) H. Forster et al. Phytopathology 94:163, 2004. (2) B. Williamson et al. Mol. Plant Pathol. 8:561. 2007. (3) L. F. Yourman and S. N. Jeffers. Plant Dis. 83:569, 1999.

scholarly journals First Report of Fenpyrazamine Resistance in Botrytis cinerea from Strawberry Fields in Spain

2018 ◽  
Vol 19 (1) ◽  
pp. 45-45
Author(s):  
Dolores Fernández-Ortuño ◽  
Alejandra Vielba-Fernández ◽  
Alejandro Pérez-García ◽  
Juan A. Torés ◽  
Antonio de Vicente
Keyword(s):  
Botrytis Cinerea ◽  
Gray Mold ◽  
In Vivo Studies ◽  
Cross Resistance ◽  
In Vitro Tests ◽  
Class Iii ◽  
Single Spore ◽  
First Report

Botrytis cinerea Pers. is an important fungal pathogen responsible for gray mold, one of the most economically important diseases of strawberry (Fragaria × ananassa) worldwide. The primary disease management strategy involves the application of different classes of fungicides, including the sterol biosynthesis inhibitor class III fungicide fenpyrazamine. In 2014 and 2015, strawberries affected with gray mold symptoms were collected from eight locations in Huelva, where fenhexamid had been used extensively. Twenty-five B. cinerea single-spore isolates were examined to determine EC50 values and to determine a discriminatory dose to monitor fenpyrazamine resistance in the field in future studies. The in vitro tests divided the isolates into two groups: 15 sensitive (EC50 from 0.02 to 1.3 μg/ml) and 10 resistant (EC50 from 50.1 to 172.6 μg/ml), which showed cross-resistance with fenhexamid. Performance of fenpyrazamine in in vivo studies was also carried out. Only the fenpyrazamine-resistant isolates developed gray mold on the fungicide-treated fruit. This is the first report of fenpyrazamine resistance in B. cinerea from strawberry fields in Spain and cross-resistance with fenhexamid.

scholarly journals Resistance to Pyraclostrobin and Boscalid in Populations of Botrytis cinerea from Stored Apples in Washington State

Plant Disease ◽  
2010 ◽  
Vol 94 (5) ◽  
pp. 604-612 ◽  
Author(s):  
Y. K. Kim ◽  
C. L. Xiao
Keyword(s):  
Botrytis Cinerea ◽  
Fungicide Resistance ◽  
Mycelial Growth ◽  
Gray Mold ◽  
Apple Fruit ◽  
Conidial Germination ◽  
Postharvest Disease ◽  
Cross Resistance ◽  
Baseline Sensitivity

Gray mold caused by Botrytis cinerea is a major postharvest disease of apple. Pristine, a formulated mixture of pyraclostrobin and boscalid, was recently registered for use on apple. Pristine applied within 2 weeks before harvest is effective in controlling gray mold in stored apple fruit. To determine the baseline sensitivity of B. cinerea populations to these fungicides, 40 isolates from organic and 80 from conventional apple orchards where Pristine had not been used were tested for mycelial growth or conidial germination on fungicide-amended media. To monitor fungicide resistance, gray-mold-decayed apple fruit originating from orchards in which Pristine had been used were sampled from a fruit packinghouse. Isolates of B. cinerea recovered from the fruit were tested for resistance to the two fungicides. In the in vivo study in the orchards, Pristine was applied to fruit 1 day before harvest. Fruit were then harvested, wounded, and inoculated with isolates exhibiting different fungicide-resistance phenotypes. Fruit were stored at 0°C for 8 weeks for decay development. The effective concentration that inhibits mycelial growth by 50% relative to the control (EC50) values for sensitive isolates ranged from 0.008 to 0.132 μg/ml (mean = 0.043, n = 116) for pyraclostrobin and from 0.003 to 0.183 μg/ml (mean = 0.075, n = 117) for Pristine in a mycelial growth assay on potato dextrose agar. The EC50 values of boscalid for sensitive isolates ranged from 0.065 to 1.538 μg/ml (mean = 0.631, n = 29) in a conidial germination assay on water agar. Four isolates were resistant to pyraclostrobin, with resistance factors (RFs) ranging from 12 to 4,193. Of the four pyraclostrobin-resistant isolates, one also was resistant to boscalid (RF = 14) and Pristine (RF = 373), and two exhibited reduced sensitivity to Pristine (RF = 16 and 17). The minimum inhibitory concentration for conidial germination (for boscalid) or mycelial growth (for pyraclostrobin and Pristine) of sensitive isolates was 5 μg/ml, which is thus recommended as a discriminatory concentration for phenotyping isolates for resistance to these fungicides. Of the 56 isolates obtained from decayed apple fruit that had been exposed to Pristine, 11 (approximately 20%) were resistant to both pyraclostrobin and boscalid and 1 was resistant only to pyraclostrobin. Of the additional 43 isolates obtained from decayed apple fruit originating from an organic orchard, 3 were resistant only to pyraclostrobin, 2 were resistant only to boscalid, and 2 were resistant to both fungicides. It appeared that there was no cross resistance between pyraclostrobin and boscalid because of the existence of isolates resistant only to either pyraclostrobin or boscalid. Pristine applied at label rate in the orchard failed to control gray mold on apple fruit inoculated with the Pristine-resistant isolates. This is the first report of multiple resistance to pyraclostrobin, boscalid, and Pristine in field populations of B. cinerea. Our results suggest that the development of dual resistance to pyraclostrobin and boscalid in B. cinerea populations could result in the failure to control gray mold with Pristine.

scholarly journals Resistance to Cyprodinil and Lack of Fludioxonil Resistance in Botrytis cinerea Isolates from Strawberry in North and South Carolina

Plant Disease ◽  
2013 ◽  
Vol 97 (1) ◽  
pp. 81-85 ◽  
Author(s):  
Dolores Fernández-Ortuño ◽  
Fengping Chen ◽  
Guido Schnabel
Keyword(s):  
South Carolina ◽  
Multidrug Resistance ◽  
Botrytis Cinerea ◽  
The United States ◽  
Gray Mold ◽  
Cross Resistance ◽  
Single Spore ◽  
Moderately Resistant ◽  
North And South

Chemical control of gray mold of strawberry caused by Botrytis cinerea is essential to prevent pre- and postharvest fruit decay. For more than 10 years, the anilinopyrimidine (AP) cyprodinil and the phenylpyrrole fludioxonil (Switch 62.5WG) have been available to commercial strawberry producers in the United States for gray mold control. Both active ingredients are site-specific inhibitors and, thus, prone to resistance development. In this study, 217 single-spore isolates of B. cinerea from 11 commercial strawberry fields in North and South Carolina were examined for sensitivity to both fungicides. Isolates that were sensitive (53%), moderately resistant (30%), or resistant (17%) to cyprodinil were identified based on germ tube inhibition at discriminatory doses of cyprodinil at 1 and 25 mg/liter at 10 of the 11 locations. None of the isolates was fludioxonil resistant. Phenotypes that were moderately resistant or resistant to cyprodinil were not associated with fitness penalties for mycelial growth rate, spore production, or osmotic sensitivity. Detached fruit assays demonstrated cross resistance between the two AP fungicides cyprodinil and pyrimethanil, and that isolates that were characterized in vitro as moderately resistant or resistant were equivalent in pathogenicity on fruit sprayed with pyrimethanil (currently the only AP registered in strawberry as a solo formulation). This suggests that the in vitro distinction of moderately resistant and resistant isolates is of little if any field relevance. The absence of cross-resistance with fludioxonil, iprodione, cycloheximide, and tolnaftate indicated that multidrug resistance in the form of multidrug resistance phenotypes was unlikely to be involved in conferring resistance to APs in our isolates. Implications for resistance management and disease control are discussed.

scholarly journals Activity of the Novel Succinate Dehydrogenase Inhibitor Fungicide Pydiflumetofen Against SDHI-Sensitive and SDHI-Resistant Isolates of Botrytis cinerea and Efficacy Against Gray Mold

Plant Disease ◽  
2020 ◽  
Vol 104 (8) ◽  
pp. 2168-2173 ◽  
Author(s):  
Leiming He ◽  
Kaidi Cui ◽  
Yufei Song ◽  
Tongtong Li ◽  
Ning Liu ◽  
...  
Keyword(s):  
Succinate Dehydrogenase ◽  
Botrytis Cinerea ◽  
Gray Mold ◽  
Effective Control ◽  
The Novel ◽  
Baseline Sensitivity ◽  
Single Spore ◽  
Significant Difference ◽  
Low Levels ◽  
Succinate Dehydrogenase Inhibitor

Succinate dehydrogenase inhibitor (SDHI) fungicides are currently the most frequently used fungicides for controlling gray mold. However, isolates of Botrytis cinerea resistant to SDHI fungicides have emerged in the field. Pydiflumetofen is a new SDHI fungicide that can control a variety of fungal diseases, but its efficacy against gray mold and whether the activity of pydiflumetofen is affected by the current SDHI-resistant isolates is currently unknown. The sensitivity of 291 single-spore B. cinerea isolates collected from 2017 to 2019 to pydiflumetofen was determined by spore germination inhibition assays. The mean EC50 value (fungicide concentration resulting in a 50% inhibition compared with that of the control) of pydiflumetofen was 0.06 ± 0.01, 0.07 ± 0.02, and 0.05 ± 0.02 mg/liter in 2017, 2018, and 2019, respectively. There was no significant difference in the sensitivity of B. cinerea to pydiflumetofen among the 3 years. Furthermore, pydiflumetofen at 300 mg/liter effectively controlled gray mold on cucumber leaves (80.9%), and its efficacy was superior to that of boscalid at 400 mg/liter (42.7%). The isolates carrying P225F, N230I, H272Y, and H272R mutations in the SdhB subunit were associated with the less sensitivity of B. cinerea to SDHI fungicides. After establishing the baseline sensitivity of B. cinerea to pydiflumetofen (EC50 of 0.03 ± 0.003 mg/liter), we found that the P225F and H272Y mutant isolates showed low to moderate levels of resistance to pydiflumetofen, and the H272R and N230I mutant isolates showed low levels of resistance. The reduced sensitivity to pydiflumetofen resulted from the positive correlation of pydiflumetofen with the other four SDHI fungicides (i.e., boscalid, fluopyram, isopyrazam, and benzovindiflupyr). These results suggest that pydiflumetofen provides effective control for the management of gray mold but must be used with caution.

scholarly journals Sensitivity of Mycosphaerella fijiensis from Banana to Trifloxystrobin

Plant Disease ◽  
2001 ◽  
Vol 85 (12) ◽  
pp. 1264-1270 ◽  
Author(s):  
K. M. Chin ◽  
M. Wirz ◽  
D. Laird
Keyword(s):  
Cross Resistance ◽  
In Vitro Tests ◽  
Mycosphaerella Fijiensis ◽  
In Planta ◽  
Baseline Sensitivity ◽  
Single Spore ◽  
Resistance Factors ◽  
Development Site ◽  
Disease Pressure

An ascospore germination method was developed and validated to assess the sensitivity of bulk samples of Mycosphaerella fijiensis to trifloxystrobin. Using this method, the sensitivity of 142 ascospore samples from banana plantations not treated with strobilurins was analyzed to establish a baseline of pathogen sensitivity. A bulk method was utilized for monitoring purposes because it avoids potential complications due to the isolation and propagation of single-spore isolates and enables the testing of larger samples. Following intensive use of strobilurins (6 to 11 applications per year) over 4 years, under conditions of high disease pressure and the absence of sanitary measures at a development site in Costa Rica, bulk samples with 50% effective concentration (EC50) resistance factors (RFs) in excess of 500 compared with the mean baseline sensitivity were detected. Single-ascospore isolates derived from spores germinating at the discriminatory dose of 3 μg/ml were also resistant, suggesting that the frequency of resistant individuals in bulk samples could be estimated from the relative numbers of ascospores growing at this dose. The resistance of selected isolates was confirmed in planta. In vitro tests with four resistant and two sensitive single-ascospore isolates collected from different locations and times indicated possible cross-resistance of trifloxystrobin to azoxystrobin, famoxadone, and fenamidone, but not to propiconazole.

scholarly journals First Report of Leaf Spot Caused by Botrytis cinerea on Cardamine hupingshanensis in China

Plant Disease ◽  
2021 ◽  
Author(s):  
Jun Guo ◽  
Jin Chen ◽  
Zhao Hu ◽  
Jie Zhong ◽  
Jun Zi Zhu
Keyword(s):  
Botrytis Cinerea ◽  
Morphological Characteristics ◽  
Gray Mold ◽  
Hunan Province ◽  
Conidial Suspension ◽  
Heat Shock Protein 60 ◽  
Basal Cells ◽  
Single Spore ◽  
Internal Transcribed Spacer Region ◽  
First Report

Cardamine hupingshanensis is a selenium (Se) and cadmium (Cd) hyperaccumulator plant distributed in wetlands along the Wuling Mountains of China (Zhou et al. 2018). In March of 2020, a disease with symptoms similar to gray mold was observed on leaves of C. hupingshanensis in a nursery located in Changsha, Hunan Province, China. Almost 40% of the C. hupingshanensis (200 plants) were infected. Initially, small spots were scattered across the leaf surface or margin. As disease progressed, small spots enlarged to dark brown lesions, with green-gray, conidia containing mold layer under humid conditions. Small leaf pieces were cut from the lesion margins and were sterilized with 70% ethanol for 10 s, 2% NaOCl for 2 min, rinsed with sterilized distilled water for three times, and then placed on potato dextrose agar (PDA) medium at 22°C in the dark. Seven similar colonies were consistently isolated from seven samples and further purified by single-spore isolation. Strains cultured on PDA were initially white, forming gray-white aerial mycelia, then turned gray and produced sclerotia after incubation for 2 weeks, which were brown to blackish, irregular, 0.8 to 3.0 × 1.2 to 3.5 mm (n=50). Conidia were unicellular, globose or oval, colourless, 7.5 to 12.0 × 5.5 to 8.3 μm (n=50). Conidiophores arose singly or in group, straight or flexuous, septate, brownish to light brown, with enlarged basal cells, 12.5 to 22.1 × 120.7 to 310.3 μm. Based on their morphological characteristics in culture, the isolates were putatively identified as Botrytis cinerea (Ellis 1971). Genomic DNA of four representative isolates, HNSMJ-1 to HNSMJ-4, were extracted by CTAB method. The internal transcribed spacer region (ITS), glyceraldehyde-3-phosphate dehydrogenase gene (G3PDH), heat-shock protein 60 gene (HSP60), ATP-dependent RNA helicaseDBP7 gene (MS547) and DNA-dependent RNA polymerase subunit II gene (RPB2) were amplified and sequenced using the primers described previously (Aktaruzzaman et al. 2018) (MW820311, MW831620, MW831628, MW831623 and MW831629 for HNSMJ-1; MW314722, MW316616, MW316617, MW316618 and MW316619 for HNSMJ-2; MW820519, MW831621, MW831627, MW831624 and MW831631 for HNSMJ-3; MW820601, MW831622, MW831626, MW831625 and MW831630 for HNSMJ-4). BLAST searches showed 99.43 to 99.90% identity to the corresponding sequences of B. cinerea strains, such as HJ-5 (MF426032.1, MN448500.1, MK791187.1, MH727700.1 and KX867998.1). A combined phylogenetic tree using the ITS, G3PDH, HSP60 and RPB2 sequences was constructed by neighbor-joining method in MEGA 6. It revealed that HNSMJ-1 to HNSMJ-4 clustered in the B. cinerea clade. Pathogenicity tests were performed on healthy pot-grown C. hupingshanensis plants. Leaves were surface-sterilized and sprayed with conidial suspension (106 conidia/ mL), with sterile water served as controls. All plants were kept in growth chamber with 85% humidity at 25℃ following a 16 h day-8 h night cycle. The experiment was repeated twice, with each three replications. After 4 to 7 days, symptoms similar to those observed in the field developed on the inoculated leaves, whereas controls remained healthy. The pathogen was reisolated from symptomatic tissues and identified using molecular methods, confirming Koch’s postulates. B. cinerea has already been reported from China on C. lyrate (Zhang 2006), a different species of C. hupingshanensis. To the best of our knowledge, this is the first report of B. cinerea causing gray mold on C. hupingshanensis in China and worldwide. Based on the widespread damage in the nursery, appropriate control strategies should be adopted. This study provides a basis for studying the epidemic and management of the disease.

scholarly journals Point Mutations in the β-Tubulin of Phytophthora sojae Confer Resistance to Ethaboxam

2019 ◽  
Vol 109 (12) ◽  
pp. 2096-2106 ◽  
Author(s):  
Qin Peng ◽  
Zhiwen Wang ◽  
Yuan Fang ◽  
Weizhen Wang ◽  
Xingkai Cheng ◽  
...  
Keyword(s):  
Fungicide Resistance ◽  
Germination Rate ◽  
Management Strategies ◽  
Resistance Management ◽  
Point Mutations ◽  
Phytophthora Sojae ◽  
Cross Resistance ◽  
Baseline Sensitivity ◽  
Resistant Mutants ◽  
Β Tubulin

Ethaboxam is a β-tubulin inhibitor registered for the control of oomycete pathogens. The current study was established to determine the ethaboxam sensitivity of the plant pathogen Phytophthora sojae and investigate the potential for the emergence of fungicide resistance. The effective concentration for 50% inhibition (EC50) of 112 Phytophthora sojae isolates exhibited a unimodal distribution with a mean EC50 for ethaboxam of 0.033 µg/ml. Establishing this baseline sensitivity provided critical data for monitoring changes in ethaboxam-sensitivity in field populations. The potential for fungicide resistance was investigated using adaptation on ethaboxam-amended V8 agar, which resulted in the isolation of 20 resistant mutants. An assessment of the biological characteristics of the mutants including mycelial growth, sporulation, germination rate and pathogenicity indicated that the resistance risk in Phytophthora sojae was low to medium with no cross-resistance between ethaboxam and cymoxanil, metalaxyl, flumorph, and oxathiapiprolin being detected. However, positive cross-resistance was found between ethaboxam and zoxamide for Q8L and I258V but negative cross-resistance for C165Y. Further investigation revealed that the ethaboxam-resistant mutants had point mutations at amino acids Q8L, C165Y, or I258V of their β-tubulin protein sequences. CRISPR/Cas9-mediated transformation experiments confirmed that the Q8L, C165Y, or I258V mutations could confer ethaboxam resistance in Phytophthora sojae and that the C165Y mutation induces high levels of resistance. Taken together, the results of the study provide essential data for monitoring the emergence of resistance and resistance management strategies for ethaboxam, as well as for improving the design of novel β-tubulin inhibitors for future development.

scholarly journals Resistance to Fluopyram, Fluxapyroxad, and Penthiopyrad in Botrytis cinerea from Strawberry

Plant Disease ◽  
2014 ◽  
Vol 98 (4) ◽  
pp. 532-539 ◽  
Author(s):  
Achour Amiri ◽  
Stacy M. Heath ◽  
Natalia A. Peres
Keyword(s):  
Succinate Dehydrogenase ◽  
Botrytis Cinerea ◽  
High Resistance ◽  
Gray Mold ◽  
Cross Resistance ◽  
The Novel ◽  
Resistance Development ◽  
Dehydrogenase Gene ◽  
Resistance Patterns ◽  
Subunit B

Succinate dehydrogenase inhibitors (SDHIs) constitute a mainstay in management of gray mold caused by Botrytis cinerea in strawberry and several other crops. In this study, we investigated the risks of resistance development to three newer SDHIs (i.e., fluopyram, fluxapyroxad, and penthiopyrad) and their cross-resistance with the previously registered boscalid. We investigated the mutations in the SdhB subunit and evaluated their impact on microbial fitness in field populations of B. cinerea. Amino acid substitutions associated with resistance to SDHIs were detected at three codons of the SdhB subunit (BH272R/Y/L, BP225F, and BN230I) in the succinate dehydrogenase gene of field isolates from Florida. The BH272R, BH272Y, BH272L, BP225F, and BN230I mutations were detected at frequencies of 51.5, 28.0, 0.5, 2.5, and 4%, respectively. Strong cross-resistance patterns were evident between boscalid and fluxapyroxad and penthiopyrad but not with fluopyram, except in BH272L, BP225F, and BN230I mutants. All five mutations conferred moderate to very high resistance to boscalid whereas the BH272Y conferred resistance to fluxapyroxad and penthiopyrad. The BH272L, BN230I, and BP225F mutations conferred high resistance to all four SDHIs tested. Resistance monitoring following the first use of penthiopyrad in strawberry fields in Florida in 2013 suggests potential for quick selection for highly resistant populations and warrants careful use of the newer SDHIs. No evidence of major fitness costs due to the mutations in the SdhB subunit was found, which indicates the potential ability of the mutants to survive and compete with wild-type isolates. Our study suggests high risks for rapid widespread occurrence of B. cinerea populations resistant to the novel SDHIs unless appropriate rotation strategies are implemented immediately upon registration.

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