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1.
ABSTRACT Single-conidial isolates of Uncinula necator from (i) a population representing two vineyards with no previous exposure to sterol demethylation inhibitor (DMI) fungicides ("unexposed," n = 77) and (ii) a population representing two vineyards in which powdery mildew was poorly controlled by triadimefon after prolonged DMI use ("selected," n = 82) were assayed to determine distributions of sensitivities to the DMI fungicides triadimenol (the active form of triadimefon), myclobutanil, and fenarimol. Median 50% effective dose (ED(50)) values (micrograms per milliliter) in the selected versus unexposed populations were 0.06 versus 1.9 for triadimenol, 0.03 versus 0.23 for myclobutanil, and 0.03 versus 0.07 for fenarimol, respectively. Isolates were grouped into sensitivity classes according to their ED(50) values, and those from the selected population were categorized as resistant if the frequency of their sensitivity class had increased significantly relative to levels found in the unexposed population (ED(50) values exceeding 0.56, 0.18, and 0.18 mug/ml for triadimenol, myclobutanil, and fenarimol, respectively). Of the 76 isolates defined as resistant to triadimenol, 64% were classified as cross-resistant to myclobutanil, 18% were classified as cross-resistant to fenarimol, and 17% were classified as resistant to all three fungicides; 25% of the isolates classified as resistant to myclobutanil also were classified as resistant to fenarimol. Similar cross-resistance relationships were revealed when all isolates were examined by regressing log ED(50) values for each fungicide against those for the remaining two fungicides to determine the correlation coefficients (e.g., r = 0.85 for triadimenol versus myclobutanil and 0.56 for triadimenol versus fenarimol). The restricted levels of cross-resistance indicated by these data, particularly between fenarimol and the other two fungicides, is in sharp contrast to the high levels of cross-resistance among DMIs reported for some other pathogens and has significant implications with respect to programs for managing grapevine powdery mildew and DMI resistance.  相似文献   

2.
In late 2003, nine populations of Sclerotinia homoeocarpa in Ontario Canada (seven of which had been previously sampled in early 1994, prior to the registration of sterol demethylation-inhibiting (DMI) fungicides for turf disease control in Canada) were sampled and tested for sensitivity to propiconazole. Four of the nine populations had not been treated with DMI fungicides during the intervening years, and isolates from these locations were sensitive to propiconazole (geometric mean EC50 values of 0·005–0·012 µ g mL−1, compared with 0·005–0·008 µ g mL−1 for the original 1994 populations). Among the five populations from 2003 that had been exposed to DMI fungicides, mean EC50 values were significantly greater, ranging from 0·020 to 0·048 µ g mL−1. A significant correlation of determination was found between estimated number of fungicide applications and log EC50 ( R 2 = 0·832, P  = 0·0001), and the equation predicted that 42·3 applications of propiconazole would be needed to bring a sensitive population (EC50 < 0·01  µ g mL−1) to a resistant level (EC50 > 0·10  µ g mL−1). Fungicide sensitivity vs. duration of fungicide efficacy was also tested, and it was found that isolates with decreased sensitivity were able to more quickly overcome the inhibitory effects of fungicide application, reducing the duration of control from 3 weeks to 2 weeks.  相似文献   

3.
Isolates of Sclerotinia homoeocarpa were collected from across southern Ontario from areas where demethylation inhibiting fungicides reportedly had never been used. Forty of these isolates with propiconazole EC50 values ranging from 0.003 to 0.069 µg ml-1 were inoculated onto creeping bentgrass (Agrostis palustris) in summer 1995 and summer 1996 to assess virulence. Each isolate was grown on mixed cereal grains, dried, ground up and applied separately at a rate of 10 g m-2 to 0.25 m2 plots with three replicates per isolate. For both years, no spots were visible on the plots at time of inoculation; however, by the end of each experiment, there were up to 180 spots per plot with significant differences between isolates. Growth rate in culture was not significantly related to fungicide sensitivity (log-EC50 values). Statistically significant negative relationships were found in both years between AUDPC and log-EC50 values. These significant relationships imply that in the absence of propiconazole use, isolates that are more sensitive to propiconazole may out-compete isolates that are less sensitive. However, further study is required to determine the time frame for this to occur, and whether DMI-resistance prevention strategies can feasibly be based on the existence of resistance-related fitness costs.  相似文献   

4.
ABSTRACT Monoconidial isolates of Venturia inaequalis were collected in 1990 and 1991 from orchards in New York, Michigan, and Nova Scotia that had never or only sporadically been treated with fungicides acting as sterol demethylation inhibitors (DMIs). Sensitivities of isolates to two representative DMIs (fenarimol and myclobutanil) were determined by a sensitivity test based on the relative growth (RG) of mycelial colonies at one discriminatory dose. Mean isolate sensitivities were not significantly different (P > 0.2) for the majority of the populations tested, and all sensitivity data obtained from these sites were combined to provide a baseline distribution of isolate sensitivities for both fenarimol and myclobutanil. The baseline distributions were compared with isolate sensitivities determined for an experimental orchard in Nova Scotia with a documented case of DMI resistance and for a commercial orchard in Michigan with a long history of DMI use and first evidence of practical DMI resistance. For both DMIs tested and in both treated orchards, frequencies of isolates with RG values <80 had decreased or only slightly increased compared to the baseline population. In contrast, frequencies of isolates with RG values >80 had increased more than 20-fold over baseline levels. Thus, isolates with RG values >80 were rated DMI resistant. The validity of a qualitative isolate classification was tested in controlled infection studies. At doses of fenarimol and myclobutanil recommended for commercial control of apple scab, reproduction of a typical sensitive isolate on treated apple leaves was suppressed completely. Lesions caused by a resistant isolate continued to expand and produced abundant conidia. Statistical analysis of orchard sensitivities revealed that the analysis of isolate counts grouped into the categories DMI sensitive or resistant was most indicative in comparisons of orchard sensitivities aimed at detection of practical DMI resistance. A high degree of cross-resistance between fenarimol and myclobutanil indicated that sensitivity tests with one of the DMIs employed as the diagnostic tool in this study can serve as a test for other DMIs.  相似文献   

5.
系统比较了从云南省主要葡萄产区采集的57株葡萄胶胞炭疽菌Colletotrichum gloeosporioides对三唑类脱甲基抑制剂烯唑醇、腈菌唑及咪唑类脱甲基抑制剂咪鲜胺的敏感性、交互敏感性及敏感性与生存适合度的相关性等指标。结果表明:供试菌株对咪鲜胺的EC50值在0.01~1.58 mg/L之间,高于其对烯唑醇(EC50值为0.05~25.45 mg/L)和腈菌唑(EC50值为0.49~192.93 mg/L)的敏感性;部分菌株对烯唑醇和腈菌唑的敏感性显著降低,而对咪鲜胺仍保持较高的敏感性;供试菌株对烯唑醇和腈菌唑的敏感性具有显著的相关性,而对咪鲜胺的敏感性与对烯唑醇和腈菌唑的敏感性之间则无显著相关性。低敏感性菌株的致病力和菌落生长速率与敏感菌株无显著差异,具有较高的生存适合度。  相似文献   

6.
The cytochrome P450 sterol 14α-demethylase gene (MfCYP51) from Monilinia fructicola (G. Wint.) Honey was cloned and sequenced. The gene was 1680 bp in length (including introns) and was predicted to have two introns of 54 and 57 bp. The nucleotide sequence was 82.1, 53.4, 47.1, 45.1, and 33.6% and the amino acid sequence was 89.7, 76.1, 76.1, 71.8, and 66.9% identical to the CYP51 genes from Botrytis cinerea, Tapesia yallundae, T. acuformis, Erysiphe graminis, and Uncinula necator, respectively. Expression of MfCYP51 in PDR5::TN5 deficient Saccharomyces cerevisiae resulted in reduced sensitivity of the yeast transformants to myclobutanil but not to propiconazole, fenbuconazole or tebuconazole. A wildtype population of 33 M. fructicola isolates was significantly less sensitive to myclobutanil than to propiconazole, fenbuconazole, and tebuconazole. The sensitivity of the isolates to myclobutanil and the three other DMI fungicides included in this study was correlated positively, suggesting a similar or identical mode of action. The low sensitivity in M. fructicola wildtype isolates to myclobutanil could result from a less effective binding potential of the fungicide to the 14α-demethylase.  相似文献   

7.
2013年湖北省小麦赤霉病菌对多菌灵和戊唑醇的敏感性   总被引：1，自引：1，他引：0  
2013年从湖北省7个小麦主产区分离获得106株禾谷镰刀菌,测定了其对戊唑醇和多菌灵的敏感性。结果表明:戊唑醇和多菌灵对所有供试菌株的EC50值分别为0.064~0.778和0.090~0.858 mg/L。采用SAS软件的W法对EC50分布进行了正态性检验,表明106株菌株对戊唑醇和多菌灵敏感性的频率分布符合正态分布,其EC50平均值分别为(0.383±0.129)和(0.526±0.151)mg/L。不同地区来源的菌株对两种药剂的敏感性存在显著差异,其中襄阳的菌株对两种药剂的敏感性显著低于其他6个地区的。研究结果显示:湖北省小麦赤霉病菌未出现对戊唑醇和多菌灵抗性菌群,两种药剂用于防治小麦赤霉病仍具有使用价值。  相似文献   

8.
Stem rot caused by Lasiodiplodia theobromae is an important postharvest disease of papaya in Brazil, responsible for reducing the quality and quantity of fruits. Fungicide use is one of the main disease management measures. However, there are no estimates available of pathogen sensitivity to commonly employed fungicides. Therefore, the EC50 from 120 isolates of L. theobromae from northeastern Brazil, representative of six populations of the pathogen, was estimated in vitro for fungicides of the methyl benzimidazole carbamates—MBC (benomyl and thiabendazole) and demethylation-inhibiting—DMI (imazalil, prochloraz, tebuconazole) groups. Mycelial growth on fungicide-free media and virulence on papaya fruits of the MBC-sensitive and non-sensitive isolates were compared. For MBCs, 8.4% of isolates were non-sensitive to fungicides. For the remaining 91.6%, the mean EC50 ranged from 0.002 to 0.13 μg ml−1 and 0.36 to 1.27 μg ml−1 for benomyl and thiabendazole, respectively. For DMIs, the mean EC50 range for imazalil was 0.001 to 2.27 μg ml−1, 0.04 to 1.75 μg ml−1 for prochloraz, and 0.14 to 4.05 μg ml−1 for tebuconazole. The EC50 values of non-sensitive isolates were significantly (P≤0.05) higher those for the sensitive isolates for each of the DMI fungicides. Differences (P≤0.05) were found in the levels of sensitivity to DMI fungicides among the isolate populations associated with orchards. The populations from two orchards were less sensitive to DMIs. No solid evidence was found for fitness costs relating to MBC non-sensitive isolates because mycelial growth in fungicide-free media and virulence on papaya fruits were similar to those of sensitive isolates.  相似文献   

9.
Thirty single-spore isolates of Cercospora beticola, collected from several fields in northern Greece, representing a broad spectrum sensitivity to the sterol demethylation-inhibiting (DMIs) fungicide flutriafol, were tested for sensitivity to eleven other sterol biosynthesis-inhibiting (SBI) fungicides and to the guanidine fungicide dodine. Sensitivity was measured as EC50 values for each fungicide and log-transformed EC50 values to each fungicide were pairwise correlated and the correlation coefficient estimated. These pairwise comparisons showed high correlation coefficients between the DMIs suggesting a cross-resistance relationship between these fungicides. However, the degree of cross-resistance between DMIs varied greatly. Conversely, low correlation coefficients were obtained for the pair-wise comparisons with the morpholine fungicide fenpropimorph suggesting a lack of cross-resistance between morpholines and DMIs in C. beticola. Similarly, there was no correlation between the sensitivity (EC50 values) to dodine and all the other fungicides tested, indicating that there was no negative cross-resistance relationship between dodine and SBIs in C. beticola. Based on these results, combinations or alternations of fungicides which show no cross-resistance relationship should be used to control the disease in areas where reduced sensitivity to DMIs has been already observed.  相似文献   

10.
Monilia yunnanensis was recently identified as a new species causing brown rot of peach in China. Sterol 14α-demethylase inhibitors (DMIs) continue to be important in the management of brown rot of Monilinia spp. worldwide. Tebuconazole and triadimefon are two kinds of DMI fungicides that may be used for brown rot control in China. To establish the baseline sensitivity of M. yunnanensis to these two DMI fungicides, 203 M. yunnanensis single spore isolates were collected. Measurements of sensitivity to the two fungicides were based on inhibition of mycelial growth. For both fungicides, the sensitivity distribution was a unimodal curve, with an EC50 range (the effective concentration to inhibit mycelial growth by 50 %) of 0.0001–0.0644 μg/ml for tebuconazole and 0.2311–1.7477 μg/ml for triadimefon. The M. yunnanensis isolates were obtained from orchards where DMI fungicides have not been used for peach brown rot control, thus the fungicide sensitivity distribution established in this study can be considered as the baseline for monitoring the resistance development in M. yunnanensis once the DMI fungicides are used to control peach brown rot.  相似文献   

11.
Sensitivity of field isolates (121) ofBotrytis cinerea from France (1992), Germany (1979–1992), Israel (1990) and the Netherlands (1970–1989) to the triazoles tebuconazole and triadimenol, the benzimidazole benomyl and the dicarboximide vinclozolin were tested in radial growth experiments. Resistance to benomyl (in 21 to 100% of isolates tested) and vinclozolin (in 25 to 71% of isolates tested) was common in most countries. EC50s (concentrations of fungicides inhibiting radial mycelial growth ofB. cinerea on B5-agar by 50%) for tebuconazole and triadimenol ranged between 0.01–1.64 and 0.4–32.6g ml–1, respectively, and were log-normally distributed. The variation factor (ratio between EC50s of the least and most sensitive isolate tested) amounts 164 and 82 for tebuconazole and triadimenol, respectively. These values are comparable to those for azole fungicides applied in control of other pathogens. Hence, variation in sensitivity to triazoles can probably not explain limited field performance of triazoles towardsB. cinerea. Isolates from south west Germany (1992) were significantly less sensitive to tebuconazole than isolates collected earlier in Germany, Israel and the Netherlands. Such less sensitive populations may contribute to the limited field performance of DMI fungicides towardsB. cinerea. The sensitivity of isolates from south west Germany to tebuconazole was similar to that of DMI-resistant mutants generated in the laboratory. These mutants displayed stable resistance with Q-values (ratio between EC50 of resistant mutant and wild type isolate) between 5 and 20. Sensitivity of field isolates and laboratory mutants to tebuconazole and triadimenol was correlated.  相似文献   

12.
BACKGROUND: Myclobutanil, a demethylation inhibitor (DMI) fungicide, is an important fungicide for controlling apple scab and powdery mildew. Overuse of this fungicide has led to establishment of scab isolates with reduced sensitivity to this fungicide in several countries. Experiments were conducted to determine the sensitivity of the causal agent of apple scab, Venturia inaequalis (Cooke) Winter, to myclobutanil in the UK, in order to assess whether there is a relationship between fungal insensitivity and the number of DMI applications, and establishing whether fungal sensitivity varied greatly within an orchard. RESULTS: Reduced sensitivity of V. inaequalis to myclobutanil was positively related linearly to the number of DMI applications. ED50 values ranged from 0.028 to 1.017 mg L?1 (average = 0.292) for the baseline population, whereas isolates from two other orchards had much greater ED50 values, ranging from 0.085 to 5.213 mg L?1 (average = 1.852). There was significant variation in fungal sensitivity to myclobutanil among fungal isolates from different locations within a single orchard. CONCLUSIONS: Spatial spread of insensitive isolates of V. inaequalis to myclobutanil is likely to be limited in distance. Conidia may be an important source of primary inoculum. Myclobutanil should still be effective for most field isolates, but its use should be strategically integrated with other groups of fungicides. Copyright © 2009 Society of Chemical Industry  相似文献   

13.
Brown rot, caused by Moniliniafructicola (G Wint) Honey, is a serious disease of peach in all commercial peach production areas in the USA, including South Carolina where it has been primarily controlled by pre-harvest application of 14-alpha demethylation (DMI) fungicides for more than 15 years. Recently, the Qo fungicide azoxystrobin was registered for brown rot control and is currently being investigated for its potential as a DMI fungicide rotation partner because of its different mode of action. In an effort to investigate molecular mechanisms of DMI and Qo fungicide resistance in M fructicola, the ABC transporter gene MfABC1 and the alternative oxidase gene MfAOX1 were cloned to study their potential role in conferring fungicide resistance. The MfABC1 gene was 4380 bp in length and contained one intron of 71 bp. The gene revealed high amino acid homologies with atrB from Aspergillus nidulans (Eidam) Winter, an ABC transporter conferring resistance to many fungicides, including DMI fungicides. MfABC1 gene expression was induced after myclobutanil and propiconazole treatment in isolates with low sensitivity to the same fungicides, and in an isolate with high sensitivity to propiconazole. The results suggest that the MfABC1 gene may be a DMI fungicide resistance determinant in M fructicola. The alternative oxidase gene MfAOX1 from M fructicola was cloned and gene expression was analyzed. The MfAOX1 gene was 1077 bp in length and contained two introns of 54 and 67 bp. The amino acid sequence was 63.8, 63.8 and 57.7% identical to alternative oxidases from Venturia inaequalis (Cooke) Winter, Aspergillus niger van Teighem and A nidulans, respectively. MfAOX1 expression in some but not all M fructicola isolates was induced in mycelia treated with azoxystrobin. Azoxystrobin at 2 microg ml(-1) significantly induced MfAOX1 expression in isolates with low MfAOX1 constitutive expression levels.  相似文献   

14.
BACKGROUND: Management of strawberry powdery mildew, Podopshaera aphanis (Wallr.), requires numerous fungicide treatments. Limiting epidemics is heavily dependent on sterol demethylation inhibitors (DMIs) such as myclobutanil or penconazole. Recently, a noticeable reduction in the efficacy of these triazole fungicides was reported by strawberry growers in France. The goal of this study was to investigate the state of DMI sensitivity of French P. aphanis and provide tools for improved pest management. RESULTS: Using leaf disc sporulation assays, sensitivity to myclobutanil and penconazole of 23 isolates of P. aphanis was monitored. Myclobutanil EC50 ranged from less than 0.1 to 14.67 mg L?1 and for penconazole from 0.04 to 4.2 mg L?1. A cross‐analysis and a Venn diagram showed that there was reduced sensitivity and a positive correlation between the less sensitive myclobutanil and penconazole isolates; 73.9% of isolates were less sensitive to a DMI and 47.8% exhibited less sensitivity to both fungicides. CONCLUSION: The results show that sensitivity to myclobutanil and, to a lesser extent, penconazole has become less efficient in strawberry powdery mildew in France. Therefore, urgent action is required in order to document its appearance and optimise methods of control. Copyright © 2009 Society of Chemical Industry  相似文献   

15.
BACKGROUND: Cucurbit powdery mildew elicited by Podosphaera fusca (Fr.) U Braun & N Shishkoff limits crop production in Spain. Disease control is largely dependent on fungicides such as sterol demethylation inhibitors (DMIs). Fungicide resistance is an increasing problem in this pathogen. To overcome such risk, it is necessary to design rational control programmes based upon knowledge of field resistance. The aim of this study was to investigate the state of DMI sensitivity of Spanish P. fusca populations and provide tools for improved disease management. RESULTS: Using a leaf‐disc assay, sensitivity to fenarimol, myclobutanil and triadimenol of 50 isolates of P. fusca was analysed to determine discriminatory concentrations between sensitive and resistant isolates. As no clearly different groups of isolates could be identified, discriminatory concentrations were established on the basis of maximum fungicide field application rate, 100 mg L?1 for the three fungicides tested. Subsequently, a survey of DMI resistance was carried out in different provinces located in the south central area of Spain during the cucurbit growing seasons in 2002, 2003 and 2004. Examination of a collection of 250 isolates revealed that 23% were resistant to fenarimol and 7% to triadimenol, the provinces of Almería, Badajoz and Murcia being the locations with the highest frequencies of resistance. By contrast, no resistance to myclobutanil was found. CONCLUSION: Results show that fenarimol and, to a lesser extent, triadimenol have become less efficient for controlling cucurbit powdery mildew in Spain. These are important observations that should lead to reconsideration of the current disease management programmes. Copyright © 2010 Society of Chemical Industry  相似文献   

16.
桃褐腐病菌(Monilinia fructicola)对3种杀菌剂的敏感性   总被引：1，自引：0，他引：1  
采用生长速率法测定了采自北京平谷区3个桃园的125株桃褐腐病菌对甲基硫菌灵、戊唑醇和异菌脲3种杀菌剂的敏感性,发现甲基硫菌灵对桃褐腐病菌的EC50主要分布在1.0×10-5～0.2μg/mL,戊唑醇对桃褐腐病菌的EC50主要分布在0.006～0.022μg/mL之间。异菌脲对桃褐腐病菌的EC50主要分布在0.15～0.55μg/mL之间。研究结果表明,北京地区的桃褐腐病菌对这3种杀菌剂都比较敏感,未产生明显的抗药群体。建立了褐腐病菌对异菌脲抗药性的敏感基线。而且,数据分析表明:甲基硫菌灵、戊唑醇和异菌脲之间均不存在交互抗性。  相似文献   

17.
Pfeufer EE  Ngugi HK 《Phytopathology》2012,102(3):272-282
Orchard management practices, such as destroying of overwintered inoculum and limiting the number of fungicide applications, are often recommended as tactics for slowing the development of resistance to sterol demethylation-inhibitor (DMI) fungicides in populations of Venturia inaequalis. However, there is little quantitative evidence relating the use of such practices to levels of resistance in orchards. The aim of this study was to evaluate the sensitivity of V. inaequalis isolates from Pennsylvania to DMI fungicides, and to identify orchard management factors related to the incidence of resistant isolates. In total, 644 single-spore V. inaequalis cultures obtained from 20 apple orchards in 2008 or 2009 were tested for sensitivity to myclobutanil, fenbuconazole, or difenoconazole. Growers provided management history of the sampled plots. Widespread shifts toward resistance to the three fungicides were noted, with mean effective concentration for 50% inhibition (EC(50)) values of 2.136, 0.786, and 0.187 μg/ml for myclobutanil, fenbuconazole, and difenoconazole, respectively. Cross resistance to the three fungicides was documented in high correlation (Spearman's r > 0.6) between mean EC(50) values for 14 orchards. Based on a 0.5-μg/ml threshold, 66 and 26% of isolates were resistant to myclobutanil and fenbuconazole, respectively, and 22% were cross resistant to the two fungicides. A significant between-year shift toward increased resistance was noted in two of three orchards surveyed in both years. Failure to use dormant copper sprays, older trees, larger orchards, orchards with ≤10 cultivars, and application of >4 DMI sprays were positively correlated (0.0001 < P < 0.05) with the incidence of resistant isolates. Isolates from orchards with >4 DMI sprays were four times as likely to be resistant to fenbuconazole (odds ratio = 4.57; P = 0.015). Isolates from orchards without dormant copper sprays were twice as likely to be cross-shifted toward resistance to all three fungicides (odds ratio = 1.76; P = 0.048). Results identify management practices that can reduce the risk of V. inaequalis developing resistance to DMI fungicides.  相似文献   

18.
采用菌丝生长速率法和孢子萌发法,分别测定了烟草灰霉病菌对多菌灵、嘧霉胺、异菌脲和丙环唑的敏感性,同时通过离体叶片法评估了这4种杀菌剂对烟草灰霉病的保护和治疗作用。结果表明:4种杀菌剂对烟草灰霉病菌的菌丝生长和孢子萌发均表现出了不同程度的抑制活性,并对灰霉病同时具有保护和治疗作用。其中多菌灵对菌丝生长的抑制活性最强,EC50平均值为0.06 mg/L,其次为丙环唑、嘧霉胺和异菌脲,EC50平均值分别为0.36、0.53和0.60 mg/L;异菌脲和丙环唑对烟草灰霉病菌孢子萌发的抑制活性较强,EC50平均值分别为2.05和2.21 mg/L,其次为嘧霉胺和多菌灵,EC50平均值分别为10.56和131.23 mg/L。异菌脲和多菌灵对灰霉病的保护作用和治疗作用均最强,当药剂质量浓度为200 mg/L时,其对离体叶片的保护和治疗作用防效分别为100%、100%和98.3%、91.8%。研究结果可为烟草灰霉病的科学防治提供依据。  相似文献   

19.
False smut, caused by Ustilaginoidea virens, is an important emerging disease of rice (Oryza sativa L.) in China. Up to now, as most varieties with high yielding and good quality are susceptible or even highly susceptible to false smut in most rice-growing ecological regions, especially in Anhui Province, chemical control with fungicides would be an important measure for the control of this disease. The ergosterol biosynthesis inhibitor (EBI) fungicides, such as prochloraz, difenoconazole, propiconazole and tebuconazole, are extensively used in China for the control of rice diseases, such as rice sheath blight and rice blast. In this study, a total of 102 U. virens isolates (from Anhui Province of China) were tested for their sensitivity to these four EBI fungicides during the stage of mycelial growth. The EC50 ranges of values for prochloraz, difenoconazole, propiconazole and tebuconazole inhibiting mycelial growth of the 102 U. virens isolates were 0.04–0.75, 0.04–1.08, 0.04–0.38 and 0.03–0.57 μg?ml?1, with the average EC50 values of 0.32?±?0.08, 0.45?±?0.08, 0.19?±?0.03 and 0.21?±?0.06 μg?ml?1, respectively. These values suggested that the tested U. virens isolates were very sensitive to these four EBI fungicides. Results of field trials showed that two sprays of three of the fungicides exhibited greater control efficacy than a single spray for the control of rice false smut. Two sprays of each was better than a single spray for the control of rice sheath blight. Two sprays of 50% propiconazole EC at 300 g a.i. ha?1 gave the best control of rice false smut at both two sites during the two consecutive years, 2010 and 2011, with the control efficacy ranging from 71.5 to 74.3%. Sensitivity of the field U. virens isolates to EBI fungicides should be monitored. Mixtures, as well as alternation with other fungicides with different modes of action, should be tested.  相似文献   

20.
Single-lesion isolates ofCercospora beticola (n=150) were collected in 1998 from sugar beet fields in the area of Serres, N. Greece. In this area, sterol demethylation-inhibiting (DMI) fungicides have been used for almost 20 years to control sugar beet leaf spot. The sensitivity of these isolates to the DMI fungicides flutriafol and difenoconazole (EC50 values) was determined on the basis of inhibition of mycelial growth at several fungicide concentrations. The relative growth (RG) of isolates was correlated at all tested concentrations with the respective EC50 values, indicating that RG provides a reliable estimate for the sensitivity of the isolates. The highest correlation coefficients were obtained for concentrations of 1 μg ml−1 flutriafol and of 0.05 μg ml−1 difenoconazole, respectively. Consequently, they are proposed for monitoring of DMI sensitivity inC. beticola populations, as single discriminatory concentrations in a simplified test method. Based on the RG values at the discriminatory concentration of 1 μg ml−1 flutriafol,C. beticola isolates were classified as either resistant or sensitive. The efficacy of flutriafol, applied at the commercially recommended dose, in controlling Cercospora leaf spot was examined in field experiments conducted during 1999 and 2000. Disease incidence in plots artificially inoculated with resistant isolates and treated with flutriafol was significantly higher than in similar plots inoculated with sensitive strains. These results suggest that poor disease control after application of flutriafol may be based on the presence of resistant strains within the pathogen population in northern Greece. This emphasizes the risk of the development of practical resistance if there is increased frequency of such strains within the population. http://www.phytoparasitica.org posting July 13, 2003.  相似文献   

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