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 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 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.

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.

Inhibitory effects of the natural product esculetin on Phytophthora capsici and its possible mechanism

Plant Disease ◽  
2020 ◽  
Author(s):  
Bi Wang ◽  
Pirui Li ◽  
Shu Xu ◽  
Lanying Liu ◽  
Yannan Xu ◽  
...  
Keyword(s):  
Natural Product ◽  
Phytophthora Capsici ◽  
Membrane Damage ◽  
Inhibitory Effects ◽  
Baseline Sensitivity ◽  
Cell Membrane Damage ◽  
Zoospore Production ◽  
Geographical Regions ◽  
Dna And Protein Synthesis ◽  
Median Effective Concentration

Esculetin is an important plant-derived natural product that has multiple bioactivities and applications. Phytophthora capsici is a notorious plant pathogen capable of infecting a broad range of hosts. In this study, we evaluated the antifungal activity of esculetin against P. capsici. The baseline sensitivity of P. capsici to esculetin was established using 108 isolates collected from various geographical regions in the Jiangsu and Shandong Provinces of China. The median effective concentration (EC50) values for esculetin ranged from 2.08 to 16.46 μg/mL, with a mean of 6.87 ± 2.70 μg/mL, and were normally distributed. Furthermore, both zoospore production and germination were also strongly inhibited by esculetin. Importantly, esculetin exhibited protective as well as curative activities against P. capsici on tomato, and was capable of restricting the early infection of P. capsici on Nicotiana benthamiana. We found that the esculetin treatment led to cell membrane damage of P. capsici, as revealed by morphological observations and measurements of relative conductivity and malondialdehyde (MDA). Finally, our results also suggested esculetin may adversely affect P. capsici by inhibiting its DNA and protein synthesis. These findings will contribute to a broader evaluation of using esculetin to control diseases caused by P. capsici and towards a better understanding of its mode of action as a potential fungicide.

scholarly journals Baseline Sensitivity and Control Efficacy of Tetramycin Against Phytophthora capsici Isolates in China

Plant Disease ◽  
2018 ◽  
Vol 102 (5) ◽  
pp. 863-868 ◽  
Author(s):  
Dicheng Ma ◽  
Jiamei Zhu ◽  
Leiming He ◽  
Kaidi Cui ◽  
Wei Mu ◽  
...  
Keyword(s):  
Mycelial Growth ◽  
Southern China ◽  
Phytophthora Capsici ◽  
Environmental Safety ◽  
Phytophthora Blight ◽  
Baseline Sensitivity ◽  
Control Efficacy ◽  
Mean Values ◽  
Greenhouse Experiments

Tetramycin is a new biopesticide that combines high-level and broad-spectrum fungicidal activity, low toxicity, and environmental safety. In this study, 90 Phytophthora capsici isolates obtained from various regions in southern China were characterized for their baseline sensitivity to tetramycin. The protective and curative activities of tetramycin against P. capsici were determined on leaves of pepper, and the control efficacy of tetramycin in greenhouse experiments was also determined. Compared with mycelial growth, the formation of sporangia and the discharge of zoospores were inhibited by lower concentrations of tetramycin, approximately 5 µg ml−1 on V8 media. The frequency distribution curves for the tetramycin sensitivity were unimodal, with mean values for the fungicide concentration that reduced mycelial growth, sporangia formation, and zoospore discharge by 50% compared with the control of 1.18 ± 0.91, 0.64 ± 0.42, and 0.63 ± 0.30 µg ml−1, respectively. In addition, no correlation was observed between tetramycin and other fungicides tested, including mandipropamid, azoxystrobin, mefenoxam, fluazinam, fluopicolide, and famoxadone. Tetramycin exhibited both protective and curative effects against P. capsici in vitro, and its protective activity was better than its curative activity. In greenhouse experiments, tetramycin concentration of 60 and 90 µg ml−1 provided a protective control efficacy of 47.1 to 56.4% and curative efficacy of 43.3 to 52.7%. These results demonstrated that tetramycin could serve as an excellent alternative fungicide to control Phytophthora blight of pepper.

scholarly journals Baseline Sensitivity and Cross-Resistance to Succinate-Dehydrogenase-Inhibiting and Demethylation-Inhibiting Fungicides in Didymella bryoniae

Plant Disease ◽  
2012 ◽  
Vol 96 (7) ◽  
pp. 979-984 ◽  
Author(s):  
A. Thomas ◽  
D. B. Langston ◽  
K. L. Stevenson
Keyword(s):  
Succinate Dehydrogenase ◽  
Fungicide Resistance ◽  
Mycelial Growth ◽  
Effective Concentration ◽  
Cross Resistance ◽  
Didymella Bryoniae ◽  
Baseline Sensitivity ◽  
History Of ◽  
Dmi Fungicides ◽  
Positive Correlations

Didymella bryoniae, which causes gummy stem blight (GSB) of watermelon, has a history of developing resistance to fungicides, most recently the succinate-dehydrogenase-inhibiting (SDHI) fungicide boscalid. To facilitate fungicide resistance monitoring, baseline sensitivity distributions were established for demethylation-inhibiting (DMI) fungicides tebuconazole and difenoconazole and the SDHI fungicide penthiopyrad, and reestablished for the SDHI fungicide boscalid. In all, 71 isolates with no known prior exposure to SDHIs or DMIs were used to determine the effective concentration at which mycelial growth was inhibited by 50% (EC50). EC50 values for boscalid, penthiopyrad, tebuconazole, and difenoconazole were 0.018 to 0.064, 0.015 to 0.057, 0.062 to 0.385, and 0.018 to 0.048 μg/ml, with median values of 0.032, 0.026, 0.118, and 0.031 μg/ml, respectively. Significant positive correlations between the sensitivity to penthiopyrad and boscalid (P < 0.0001, r = 0.75) and between tebuconazole and difenoconazole (P < 0.0001, r = 0.59) indicate a potential for cross-resistance between chemically related fungicides. In 2009, 103 isolates from fungicidetreated watermelon fields were tested for sensitivity to boscalid and penthiopyrad using a discriminatory concentration of 3.0 μg/ml. Of the isolates tested, 82 were insensitive and 14 were sensitive to both fungicides. Because of the significant potential for cross-resistance between closely related fungicides, growers will be advised not to use both SDHIs or both DMIs successively in the same fungicide spray program.

scholarly journals Baseline Sensitivity of Guignardia citricarpa Isolates from Florida to Azoxystrobin and Pyraclostrobin

Plant Disease ◽  
2014 ◽  
Vol 98 (6) ◽  
pp. 780-789 ◽  
Author(s):  
Martha Hincapie ◽  
Nan-Yi Wang ◽  
Natalia A. Peres ◽  
Megan M. Dewdney
Keyword(s):  
Mycelial Growth ◽  
Control Measure ◽  
Black Spot ◽  
Conidial Germination ◽  
Baseline Sensitivity ◽  
Qoi Fungicides ◽  
Resistance Risk ◽  
Guignardia Citricarpa ◽  
The Mean

Citrus black spot (CBS), caused by Guignardia citricarpa, is an emerging disease in Florida. Fungicide applications are the main control measure worldwide. The in vitro activity and baseline sensitivity of G. citricarpa isolates to quinone outside inhibitor (QoI) fungicides (azoxystrobin and pyraclostrobin) were evaluated. The effective concentration needed to reduce mycelial growth or spore germination by 50% (EC50) was determined for 86 isolates obtained from Florida counties where CBS is found. The effect of salicylhydroxamic acid (SHAM) plus azoxystrobin and pyraclostrobin was also assessed for mycelial growth and conidial germination. The mean EC50 for mycelial growth for azoxystrobin was 0.027 μg/ml and that for pyraclostrobin was significantly lower at 0.007 μg/ml (P < 0.0001). Similarly, the mean EC50 for conidial germination for azoxystrobin was 0.016 μg/ml and that for pyraclostrobin was significantly lower at 0.008 μg/ml (P < 0.0001). There was no effect of SHAM on inhibition of mycelial growth or conidial germination by the QoI fungicides but SHAM slightly affected mycelium inhibition by pyraclostrobin. Cytochrome b was partially sequenced and three group 1 introns were found. One intron was immediately post G143, likely inhibiting resistance-conferring mutations at that site. It is surmised that the QoI resistance risk is low in the Florida G. citricarpa population.

Resistance Risk Evaluated by Metaflumizone Selection and the Effects on Toxicities Over Other Insecticides in Spodoptera exigua (Lepidoptera: Noctuidae)

2019 ◽  
Vol 112 (5) ◽  
pp. 2354-2361
Author(s):  
Xing-Xing Sun ◽  
Hong-Yang Li ◽  
Ying-Jie Jiang ◽  
Jun-Xi Zhang ◽  
Hui-Ling Gu ◽  
...  
Keyword(s):  
Spodoptera Exigua ◽  
Channel Blocker ◽  
Resistance Management ◽  
Cross Resistance ◽  
Realized Heritability ◽  
Sodium Channel Blocker ◽  
Resistance Risk ◽  
Resistance Evolution ◽  
Threshold Trait ◽  
Lepidoptera Noctuidae

Abstract Metaflumizone is a novel semicarbazone insecticide. It functions as a sodium channel blocker insecticide (SCBI) with excellent insecticidal activity on most economically important lepidopterous pests. This study assessed the resistance risk of Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) to metaflumizone in the laboratory and the effects of metaflumizone selection on toxicities to other insecticides. Spodoptera exigua collected from a field population at Huizhou in 2012 were successively challenged by metaflumizone to evaluate the risk of resistance evolution. Twelve generations of selection increased resistance to metaflumizone by 3.4-fold and threshold trait analysis revealed that the realized heritability (h2) of this resistance was 0.086. When h2 was equal to 0.086 and 90% of individuals were killed at each generation, LC50 to metaflumizone increased by 10-fold after 15 generations. The selection by metaflumizone did not increase the resistance to indoxacarb, chlorantraniliprole, spinosad, methomyl, or endosulfan, suggesting a lack of cross-resistance. However, metaflumizone challenge upheld the recession of resistance to emamectin benzoate, chlorfluazuron, and tebufenozide. The block of resistance drops by metaflumizone exposure implied a possible cross-resistance between metaflumizone and these three insecticides. These results contribute to integrated resistance management of S. exigua.

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