scholarly journals Wild Type Sensitivity and Mutation Analysis for Resistance Risk to Fluopicolide in Phytophthora capsici

Plant Disease ◽  
2011 ◽  
Vol 95 (12) ◽  
pp. 1535-1541 ◽  
Author(s):  
Xiao Hong Lu ◽  
Mary K. Hausbeck ◽  
Xi Li Liu ◽  
Jianjun J. Hao
Keyword(s):  
Phytophthora Capsici ◽  
The United States ◽  
Fruit Rot ◽  
Cross Resistance ◽  
Wild Type ◽  
Baseline Sensitivity ◽  
Resistance Risk ◽  
Crown Root ◽  
Zoospore Production ◽  
Resistant Mutants

Crown, root, and fruit rot caused by Phytophthora capsici is an increasing problem for vegetable growers in Michigan and the United States. The newly registered fungicide fluopicolide is effective to limit crop loss but the potential for P. capsici to develop resistance is not well known. A laboratory study assessed the risk of P. capsici developing resistance to fluopicolide. Baseline sensitivity to fluopicolide was determined using 126 P. capsici Michigan isolates. Values of effective concentrations for 50% inhibition of mycelial growth ranged from 0.08 to 0.24 μg/ml and were distributed as a unimodal curve, indicating that all isolates were sensitive to fluopicolide. Mutants resistant to fluopicolide were obtained from five isolates by screening zoospores on fluopicolide-amended (5 μg/ml) media at a mutation frequency above 1.0 × 10–7. The mutant isolates were clustered with either intermediate (resistance factor [RF] = 3.53 to 77.91) or high (RF = 2481.40 to 7034.79) resistance. Resistance was stable through 10 mycelial transfers on fungicide-free medium. All resistant mutants showed similar fitness in zoospore production, cyst germination, and virulence compared with their sensitive parents, with few exceptions. No cross-resistance was detected between fluopicolide and five other fungicides. There could be a moderately high risk of field populations of P. capsici developing resistance to fluopicolide, and populations should be monitored.

scholarly journals Baseline Sensitivity of Natural Population and Resistance of Mutants in Phytophthora capsici to Zoxamide

2011 ◽  
Vol 101 (9) ◽  
pp. 1104-1111 ◽  
Author(s):  
Yang Bi ◽  
Xiaolan Cui ◽  
Xiaohong Lu ◽  
Meng Cai ◽  
Xili Liu ◽  
...  
Keyword(s):  
Ultraviolet Irradiation ◽  
Mycelial Growth ◽  
Laboratory Experiments ◽  
Phytophthora Capsici ◽  
Cross Resistance ◽  
Wild Type ◽  
Baseline Sensitivity ◽  
Mycelial Culture ◽  
Resistance Selection ◽  
Resistant Mutants

Laboratory experiments were conducted to determine the baseline sensitivity of Phytophthora capsici and its risk for developing resistance to zoxamide. In total, 158 P. capsici isolates were collected from China. All 158 isolates were sensitive to zoxamide, with effective concentrations for 50% inhibition of mycelial growth of 0.023 to 0.383 μg/ml and a mean of 0.114 μg/ml, which showed a skewed unimodal distribution. Zoxamide-resistant mutants of P. capsici were obtained by either treating mycelial culture and zoospores with ultraviolet irradiation or adapting a culture on zoxamide-amended plates. The frequency of resistance selection averaged 1.8 × 10–7. Resistant isolates were also derived by selfing or crossing two sexually compatible isolates, resulting in a mean selection frequency of 0.47. The resistance factor (RF) for zoxamide was 25 to 100 in P. capsici mutants. Through 10 culture transfers, the mutants maintained high levels of RF (between 14 and 134) and had almost equal fitness as their wild-type parents in mycelial growth, sporulation, and virulence. There was no cross resistance between zoxamide and either flumorph, metalaxyl, azoxystrobin, or etridiazole. Based on the results above, P. capsici can develop resistance to zoxamide, and the risk is predicted to be moderate in nature.

scholarly journals Baseline Sensitivity and Resistance-Risk Assessment of Phytophthora capsici to Iprovalicarb

2010 ◽  
Vol 100 (11) ◽  
pp. 1162-1168 ◽  
Author(s):  
Xiao Hong Lu ◽  
Shu Sheng Zhu ◽  
Yang Bi ◽  
Xi Li Liu ◽  
Jianjun J. Hao
Keyword(s):  
Mycelial Growth ◽  
Phytophthora Capsici ◽  
Acid Amide ◽  
Resistance Management ◽  
Cross Resistance ◽  
Baseline Sensitivity ◽  
Resistance Risk ◽  
Zoospore Production ◽  
Caa Fungicides ◽  
Growth Characters

Iprovalicarb has been used to control Phytophthora capsici, a devastating pathogen of many economically important crops. To evaluate the risk of fungicide resistance, 158 isolates of P. capsici were examined for sensitivity to iprovalicarb by measuring mycelial growth. Values of effective concentrations for 50% mycelial growth inhibition varied from 0.2042 to 0.5540 μg/ml and averaged 0.3923 (±0.0552) μg/ml, with a unimodal distribution. This is the first report of P. capsici isolates highly resistant to iprovalicarb (resistance factor >100). Resistance of the isolates was stable through 10 transfers on iprovalicarb-free medium, and most resistant isolates had the same level of fitness (mycelial growth, zoospore production, and virulence) as their corresponding parents, indicating that iprovalicarb resistance was independent from other general growth characters. There was cross-resistance among all tested carboxylic acid amide (CAA) fungicides, including iprovalicarb, flumorph, dimethomorph, and mandipropamid, but not with non-CAA fungicides, including azoxystrobin, chlorothalonil, cymoxanil, etridiazole, metalaxyl, and zoxamide. Based on the present results, resistance risk of P. capsici to CAAs could be moderate and resistance management should be considered.

scholarly journals Characterizing Sources of Resistance to Phytophthora Blight of Pepper Caused by Phytophthora capsici in North Carolina

2019 ◽  
Vol 20 (2) ◽  
pp. 112-119
Author(s):  
Camilo H. Parada-Rojas ◽  
Lina M. Quesada-Ocampo
Keyword(s):  
North Carolina ◽  
Phytophthora Capsici ◽  
The United States ◽  
Field Trials ◽  
Fruit Rot ◽  
Phytophthora Blight ◽  
Sources Of Resistance ◽  
Crown Root ◽  
Different Levels ◽  
Important Disease

Phytophthora blight, caused by Phytophthora capsici, is an important disease of peppers in the United States and worldwide. P. capsici causes crown, root, and fruit rot as well as foliar lesions in peppers. Field trials were conducted in 2015 and 2016 to evaluate 32 commercial and experimental pepper cultivars against a mixed-isolate inoculum in North Carolina. Cultivars Martha-R and Meeting were classified as highly resistant to P. capsici, and Paladin was classified as resistant. Intermediate resistance to P. capsici in the field was observed with Fabuloso, Revolution, Vanguard, Archimedes, Aristotle, Ebano-R, and Declaration. Greenhouse experiments were conducted to determine the response of 48 pepper cultivars when inoculated individually with two isolates from North Carolina and an isolate from Michigan. Isolates exhibited different levels of virulence in pepper cultivars screened for resistance. Landraces CM334 and Fidel as well as the cultivars Martha-R, Meeting, and Intruder were categorized as highly resistant or resistant to the three isolates tested. Overall, highly resistant cultivars tended to respond similarly to field mix inoculations and greenhouse single isolate inoculations.

scholarly journals Sensitivity of Isolates of Phytophthora capsici from the Eastern United States to Fluopicolide

Plant Disease ◽  
2011 ◽  
Vol 95 (11) ◽  
pp. 1414-1419 ◽  
Author(s):  
Anthony P. Keinath ◽  
Chandrasekar S. Kousik
Keyword(s):  
United States ◽  
North Carolina ◽  
South Carolina ◽  
Mycelial Growth ◽  
Phytophthora Capsici ◽  
The United States ◽  
Eastern United States ◽  
Baseline Sensitivity ◽  
First Report ◽  
Zoospore Production

Fluopicolide, a pyridinylmethyl-benzamide fungicide, was registered in the United States in 2008 to control diseases caused by Oomycete pathogens, such as Phytophthora capsici, on cucurbit and solanaceous vegetables. The main objective of this study was to determine baseline sensitivity to fluopicolide in isolates of P. capsici from the southeastern and midwestern United States. A total of 69 isolates from Florida (14 isolates), Georgia (14 isolates), Michigan (24 isolates), North Carolina (3 isolates), and South Carolina (17 isolates) that had not been previously exposed to fluopicolide were grown on fungicide-amended medium to determine sensitivity of mycelia, sporangia, and zoospores to the fungicide. All isolates of P. capsici tested (range of 54 to 69 isolates per assay) were sensitive to fluopicolide in all four assays. The median EC50 fluopicolide concentration was 0.22, 2.08, 0.048, and 0.10 mg/liter in the mycelial growth, zoospore germination, sporangia production, and zoospore production assays, respectively. For mycelial growth and zoospore germination, isolates from Michigan had a higher mean EC50 value than isolates from the four southeastern states. This is the first report of variation in baseline sensitivity to a fungicide by P. capsici isolates from different regions of the United States. In the sporangia production and zoospore production assays, isolates from different states did not differ in sensitivity. Single rates of fluopicolide were tested with additional isolates to validate discriminatory rates for monitoring sensitivity. A concentration of 0.3 or 1.0 mg/liter is recommended for mycelial growth, and 0.1 mg/liter is recommended for sporangia and zoospore production.

scholarly journals Evaluation of a Diverse, Worldwide Collection of Wild, Cultivated, and Landrace Pepper (Capsicum annuum) for Resistance to Phytophthora Fruit Rot, Genetic Diversity, and Population Structure

2015 ◽  
Vol 105 (1) ◽  
pp. 110-118 ◽  
Author(s):  
R. P. Naegele ◽  
A. J. Tomlinson ◽  
M. K. Hausbeck
Keyword(s):  
Genetic Diversity ◽  
Population Structure ◽  
Phytophthora Capsici ◽  
The United States ◽  
Fruit Rot ◽  
Sources Of Resistance ◽  
Plant Introductions ◽  
Genetic Clusters ◽  
Commercial Breeding ◽  
Moderately Resistant

Pepper is the third most important solanaceous crop in the United States and fourth most important worldwide. To identify sources of resistance for commercial breeding, 170 pepper genotypes from five continents and 45 countries were evaluated for Phytophthora fruit rot resistance using two isolates of Phytophthora capsici. Genetic diversity and population structure were assessed on a subset of 157 genotypes using 23 polymorphic simple sequence repeats. Partial resistance and isolate-specific interactions were identified in the population at both 3 and 5 days postinoculation (dpi). Plant introductions (PIs) 640833 and 566811 were the most resistant lines evaluated at 5 dpi to isolates 12889 and OP97, with mean lesion areas less than Criollo de Morelos. Genetic diversity was moderate (0.44) in the population. The program STRUCTURE inferred four genetic clusters with moderate to very great differentiation among clusters. Most lines evaluated were susceptible or moderately susceptible at 5 dpi, and no lines evaluated were completely resistant to Phytophthora fruit rot. Significant population structure was detected when pepper varieties were grouped by predefined categories of disease resistance, continent, and country of origin. Moderately resistant or resistant PIs to both isolates of P. capsici at 5 dpi were in genetic clusters one and two.

scholarly journals Fungicide Rotation Programs for Managing Phytophthora Fruit Rot of Watermelon in Southeastern United States

2017 ◽  
Vol 18 (1) ◽  
pp. 28-34 ◽  
Author(s):  
Chandrasekar (Shaker) S. Kousik ◽  
Pingsheng Ji ◽  
Daniel S. Egel ◽  
Lina M. Quesada-Ocampo
Keyword(s):  
United States ◽  
South Carolina ◽  
Phytophthora Capsici ◽  
Southeastern United States ◽  
Heavy Rain ◽  
Integrated Approach ◽  
The United States ◽  
Fruit Rot ◽  
Management Options ◽  
Before And After

About 50% of the watermelons in the United States are produced in the southeastern states, where optimal conditions for development of Phytophthora fruit rot prevail. Phytophthora fruit rot significantly limits watermelon production by causing serious yield losses before and after fruit harvest. Efficacy of fungicide rotation programs and Melcast-scheduled sprays for managing Phytophthora fruit rot was determined by conducting experiments in Phytophthora capsici-infested fields at three locations in southeastern United States (North Carolina, South Carolina, and Georgia). The mini seedless cultivar Wonder and seeded cultivar Mickey Lee (pollenizer) were used. Five weekly applications of fungicides were made at all locations. Significant fruit rot (53 to 91%, mean 68%) was observed in the nontreated control plots in all three years (2013 to 2015) and across locations. All fungicide rotation programs significantly reduced Phytophthora fruit rot compared with nontreated controls. Overall, the rotation of Zampro alternated with Orondis was highly effective across three locations and two years. Rotations of Actigard followed by Ranman+Ridomil Gold, Presidio, V-10208, and Orondis, or rotation of Revus alternated with Presidio were similarly effective. Use of Melcast, a melon disease-forecasting tool, may occasionally enable savings of one spray application without significantly impacting control. Although many fungicides are available for use in rotations, under very heavy rain and pathogen pressure, the fungicides alone may not offer adequate protection; therefore, an integrated approach should be used with other management options including well-drained fields.

scholarly journals Mutations in ORP1 Conferring Oxathiapiprolin Resistance Confirmed by Genome Editing using CRISPR/Cas9 in Phytophthora capsici and P. sojae

2018 ◽  
Vol 108 (12) ◽  
pp. 1412-1419 ◽  
Author(s):  
Jianqiang Miao ◽  
Yuandong Chi ◽  
Dong Lin ◽  
Brett M. Tyler ◽  
Xili Liu
Keyword(s):  
Binding Protein ◽  
Phytophthora Capsici ◽  
Control Plant ◽  
Point Mutations ◽  
Wild Type ◽  
Oxysterol Binding Protein ◽  
Type Isolate ◽  
Phytophthora Spp ◽  
Zoospore Production ◽  
Wild Type Parent

Oxathiapiprolin is a novel fungicide that was recently registered in a number of countries to control plant-pathogenic oomycetes such as Phytophthora capsici. In our previous study, point mutations G770V and G839W in oxysterol binding protein-related protein 1 (ORP1) were detected in oxathiapiprolin-resistant P. capsici isolates (PcORP1). Here, we used the CRISPR/Cas9 system to verify the effects of these two point mutations on P. capsici phenotypes. Transformants containing heterozygous G770V and G839W mutations in PcORP1 showed high levels of oxathiapiprolin resistance. The G770V transformants showed otherwise similar phenotypes compared with the wild-type isolate BYA5, including sporangia and zoospore production, cyst germination, and pathogenicity. However, two independent transformants with heterozygous G839W mutations in PcORP1 could not produce sporangia. Three transformants with an unexpected point mutation in PcORP1 (ΔN837) showed high oxathiapiprolin resistance, and either similar or significantly reduced fitness compared with BYA5. The same deletion (ΔN837) was confirmed to confer oxathiapiprolin resistance in P. sojae by using CRISPR/Cas9. These homozygous P. sojae mutants also showed either similar or strongly reduced fitness compared with the wild-type parent isolate P6497. These results improve our understanding of oxathiapiprolin resistance in Phytophthora spp., and will be useful for the development of novel oxysterol-binding protein homolog inhibitor fungicides.

Sensitivity and Resistance Risk Assessment of Puccinia striiformis f. sp. tritici to Triadimefon in China

Plant Disease ◽  
2021 ◽  
Author(s):  
Gangming Zhan ◽  
Fan Ji ◽  
Jun Zhao ◽  
Yue Liu ◽  
Aihong Zhou ◽  
...  
Keyword(s):  
Point Mutation ◽  
Fungicide Resistance ◽  
Puccinia Striiformis ◽  
Germination Rate ◽  
Detection Methods ◽  
Cross Resistance ◽  
Maximal Effect ◽  
Baseline Sensitivity ◽  
Resistance Risk ◽  
Wide Range

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a destructive disease of wheat that seriously threatens production safety in wheat-producing areas worldwide. In China, the disease has been largely controlled with fungicide triadimefon. Although high levels of fungicide resistance in other fungal pathogens have been reported, failure to control Pst with any fungicides has seldomly been reported and fungicide sensitivity of Pst has not been evaluated in China. The distribution of triadimefon-resistant Pst isolates was investigated in the present study. The baseline sensitivity of 446 Pst isolates across the country to triadimefon was determined, and the concentration for 50% of maximal effect (EC50) showed a unimodal distribution curve, with a mean value of 0.19 μg mL-1. The results indicated a wide range of sensitivity to triadimefon, with more insensitive isolates collected from Pst winter-increasing areas and northwest over-summering areas, whereas more sensitive isolates were collected from southwest over-summering areas and epidemic areas of Xinjiang and Tibet. The majority of the tested Pst isolates were sensitive to triadimefon; only 6.79% had developed varying degrees of resistance. Characterization of parasitic fitness revealed that the triadimefon-resistant isolates exhibited strong adaptive traits in urediniospore germination rate, latent period, sporulation intensity, and lesion expansion rate. Positive cross-resistance was observed between triadimefon and tebuconazole or hexaconazole, but not between pyraclostrobin or flubeneteram. The point mutation Y134F in the 14α-demethylase enzyme (CYP51) was detected in triadimefon-resistant isolates. A molecular method (Kompetitive Allele Specific PCR) was established for the rapid detection of Y134F mutants in the Pst population. Two genotypes with one point mutation Y134F conferred resistance to triadimefon in Pst. The risk of resistance to triadimefon in Pst may be low to moderate. This study provided important data for establishment of high throughput molecular detection methods, fungicide resistance risk management, and the development of new target fungicides.

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 Peptide Deformylase in Staphylococcus aureus: Resistance to Inhibition Is Mediated by Mutations in the Formyltransferase Gene

2000 ◽  
Vol 44 (7) ◽  
pp. 1825-1831 ◽  
Author(s):  
Peter S. Margolis ◽  
Corinne J. Hackbarth ◽  
Dennis C. Young ◽  
Wen Wang ◽  
Dawn Chen ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Genomic Library ◽  
Specific Inhibitor ◽  
Peptide Deformylase ◽  
Cross Resistance ◽  
Loss Of Function ◽  
Wild Type ◽  
Chromosomal Dna ◽  
Resistant Mutants

ABSTRACT Peptide deformylase, a bacterial enzyme, represents a novel target for antibiotic discovery. Two deformylase homologs, defA and defB, were identified inStaphylococcus aureus. The defA homolog, located upstream of the transformylase gene, was identified by genomic analysis and was cloned from chromosomal DNA by PCR. A distinct homolog, defB, was cloned from an S. aureus genomic library by complementation of the arabinose-dependent phenotype of a P BAD -def Escherichia coli strain grown under arabinose-limiting conditions. Overexpression in E. coli of defB, but not defA, correlated to increased deformylase activity and decreased susceptibility to actinonin, a deformylase-specific inhibitor. ThedefB gene could not be disrupted in wild-type S. aureus, suggesting that this gene, which encodes a functional deformylase, is essential. In contrast, thedefA gene could be inactivated; the function of this gene is unknown. Actinonin-resistant mutants grew slowly in vitro and did not show cross-resistance to other classes of antibiotics. When compared to the parent, an actinonin-resistant strain produced an attenuated infection in a murine abscess model, indicating that this strain also has a growth disadvantage in vivo. Sequence analysis of the actinonin-resistant mutants revealed that each harbors a loss-of-function mutation in the fmt gene. Susceptibility to actinonin was restored when the wild-type fmt gene was introduced into these mutant strains. An S. aureusΔfmt strain was also resistant to actinonin, suggesting that a functional deformylase activity is not required in a strain that lacks formyltransferase activity. Accordingly, thedefB gene could be disrupted in an fmt mutant.

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