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1.
Litchi downy blight caused by Peronophythora litchii is a devastating disease of litchi plants in China. Control of litchi downy blight requires numerous fungicide applications. A new carboxylic acid amide (CAA) fungicide, mandipropamid, was examined for its in vitro effects on multiple asexual stages of four single-sporangium P. litchii isolates and protective activity against downy blight in detached fruit assays. Though mandipropamid did not affect discharge of zoospores from sporangia, it strongly inhibited mycelial growth (mean EC50 = 0.0048 μg ml−1), sporangia production (mean EC50 = 0.0032 μg ml−1), germination of encysted zoospores (mean EC50 = 0.0023 μg ml−1), and germination of sporangia (mean EC50 = 0.0061 μg ml−1). On detached fruit, 0.39, 1.56 and 6.25 μg ml−1 of mandipropamid were superior in reducing downy blight compared to metalaxyl and flumorph, however, the 25 μg ml−1 application rate was necessary for all three CAA fungicides to completely inhibit the disease. In 2007, 100 isolates from Fujian, Guangdong, and Guangxi Provinces of China were characterized for the baseline sensitivity to mandipropamid. The isolates obtained from different provinces showed similar baseline sensitivities to mandipropamid. Baseline sensitivities formed a unimodal curve with mean EC50 values of 0.0055 ± 0.0012 μg ml−1 for inhibition of mycelial growth. The described baseline sensitivities of P. litchii populations will be useful for monitoring possible shifts in sensitivity to mandipropamid.  相似文献   

2.
This work determined the sensitivity of field populations of Sclerotinia sclerotiorum (Lib.) de Bary before exposure to the fungicide fludioxonil (= baseline sensitivity) and assessed the risk of fludioxonil resistance. The mean EC50 (Effective Concentration) and Minimum inhibitory concentration (MIC) values for fludioxonil based on inhibition of mycelial growth of 120 wild-type isolates were 0.015 ± 0.005 μg/ml and <0.05 μg/ml, respectively. Positive cross-resistance was not detected between fludioxonil and benzimidazole fungicides but was detected between fludioxonil and dicarboximide fungicides which are considered as high resistance risk fungicides by FRAC, even though these fungicides have different molecular structures. By growing wild-type isolates on potato dextrose agar (PDA) containing sublethal concentrations of the fungicide, we obtained four fludioxonil-resistant mutants with resistance factors (EC50 resistant/EC50 sensitive phenotypes) >2000. The laboratory fludioxonil mutants were less fitter than their parental isolates in terms of mycelial radial growth, pathogenicity and sclerotial production. Moreover, on PDA amended with NaCl, the laboratory fludioxonil mutants grew more slowly than their fludioxonil-sensitive parents, especially at lower concentrations of NaCl. According to the fitness of mutants and the cross-resistance between fludioxonil and dicarboximide fungicides, phenylpyrroles can be considered to pose a moderate resistance risk. In a field trial, fludioxonil provided greater control (over 90% disease control) of S. sclerotiorum than iprodione.  相似文献   

3.
Since the 1980s wheat sharp eyespot (WSE) caused mainly by Rhizoctonia cerealis has become one of serious diseases of wheat in China. In this study, the sensitivity of 89 R. cerealis isolates to different fungicides was evaluated using mycelial growth inhibition assays. The results showed that all R. cerealis isolates tested were sensitive to iprodione, difenoconazole and fludioxonil with mean EC50 (effective concentration that results in 50% of mycelial growth inhibition) values of 0.419, 0.062 and 0.033 μg/ml, respectively. To evaluate the risk of fungicide resistance in R. cerealis, an attempt was made to induce resistant mutants in the laboratory. Although difenoconazole- and fludioxonil-resistant mutants were not obtained, we obtained seven independently iprodione-resistant (IR) mutants from 89 parental isolates. The EC50 values for these IR mutants were greater than 100 μg/ml, whereas those for the original wild-type counterparts were less than 1 μg/ml. After having been subcultured on PDA for 10 generations, the IR mutants did not show any decrease in resistance to iprodione. Additionally, these IR mutants also showed resistance to fludioxonil but remained sensitive to difenoconazole. Osmotic sensitivity tests showed that the IR mutants were hypersensitive to osmotic stress generated by NaCl. Inoculation tests showed that all the IR mutants lost their ability to infect the host plant. Taken together, these results indicate that the current population of R. cerealis is sensitive to these fungicides and a fitness cost is associated with iprodione-resistant mutants of R. cerealis in both osmotic stress and pathogenicity. The information obtained in this study is useful in monitoring and managing fungicide resistance in R. cerealis populations in China.  相似文献   

4.
Antifeedant, growth inhibitory and toxic effects of crude seed extracts of Annona squamosa and Annona atemoya from Fazenda Viveiro Bona, Parasisópolis – Minas Gerais, Brazil, were evaluated against the cabbage looper, Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae) using different bioassays. Crude methanolic seed extracts deterred feeding of third instar T. ni larvae in a leaf disc choice bioassay. A. squamosa was ∼10 times more active as a feeding deterrent than A. atemoya (DC50 = 2.3 mg/ml vs. 20.1 mg/ml). A. squamosa was ∼three times more active as a growth inhibitor than A. atemoya (EC50 = 38.0 ppm vs. 117.0 ppm). Methanolic seed extracts of A. squamosa and A. atemoya were toxic to third instar T. ni larvae both through topical and oral application. A. squamosa was more toxic through feeding (LC50 = 167.5 ppm vs. 382.4 ppm) whereas, A. atemoya exerted greater toxicity via topical application (LC50 = 301.3 μg/larva vs. 197.7 μg/larva). Both A. squamosa and A. atemoya extracts reduced leaf area consumption and larval growth in a greenhouse experiment. Our results indicate that both A. squamosa and A. atemoya have potential for development as botanical insecticides, especially for local use in Brazil.  相似文献   

5.
Antioxidant, antibacterial and antiviral effects of aqueous and methanol extracts of Lactuca sativa var longifolia leaves were investigated. The antioxidant activity was evaluated using the DPPH assay. The effect of the extracts against 5 Gram-positive and 6 Gram-negative bacteria was tested. The antiviral activity was determined against human cytomegalovirus (HCMV) strain AD-169 (ATCC Ref. VR 538) and coxsackie B virus type 3 (CoxB-3) using a cytopathic effect (CPE) reduction assay. The methanol extract had the highest total phenolic contents (235.31 mg CE/g extract). It exhibited a significantly (p < 0.05) greater hydroxyl radical-scavenging activity (IC50 = 3.5 μg/ml) than the aqueous extract (4.1 μg/ml). It was also the most effective extract with the lowest MIC (2.5 mg/ml) against all Gram negative and Gram positive bacteria. Methanol and aqueous extracts exhibited antiviral activity against HCMV and Cox-B3 viruses with IC50 of 200 μg/ml.  相似文献   

6.
The baseline sensitivity of Fusarium verticillioides to the novel cyanoacrylate fungicide 2-cyano-3-amino-3-phenylancryic acetate (experimental code JS399-19) was established, and its impact on the germination of rice seeds and efficacy in controlling rice bakanae disease by seed treatment were evaluated. The EC50 values for JS399-19 inhibiting mycelial growth of wild-type F. verticillioides isolates ranged from 0.162 to 0.559 μg/ml (a 3.5-fold difference between the lowest and highest value), and the average (±SE) EC50 value was 0.316 ± 0.072 μg/ml. The sensitivity curve was unimodal over the sensitive range and the sensitivity data can be used as a baseline for monitoring any future changes in sensitivity to JS399-19 by F. verticillioides populations. Germination of healthy seeds was greater than 77% for all the selected cultivars, and was unaffected by treatment with JS399-19. Treatment of infected seeds (harvested from diseased plants) with all concentrations of JS399-19 in this study significantly decreased the abnormal elongation and damping-off of seedlings in plastic bottles in the greenhouse, indicating that JS399-19 has excellent efficacy in controlling rice bakanae disease, and was safe to rice seeds. It could be used as a disinfectant of rice seeds infected by F. verticillioides. The results also suggested that the F. verticillioides isolates exhibited little sensitivity shift to this fungicide after a single application. If properly applied, JS399-19 might be used as a major fungicide or a good companion fungicide for the control of rice bakanae disease in China.  相似文献   

7.
The ascomycete fungus Sclerotinia sclerotiorum is a devastating plant pathogen notorious for its extremely broad host range. Trifloxystrobin has not been registered for control of S. sclerotiorum in China. In this study, baseline sensitivity of trifloxystrobin was established based on frequency distribution of 166 isolates' EC50 values and efficacy of trifloxystrobin was determined on potted oilseed rape plants. Trifloxystrobin EC50 values of the 166 isolates ranged from 0.01 to 0.80 μg/mL, with a mean value of 0.06 μg/mL. The frequency distribution of trifloxystrobin EC50 values was unimodal in shape, but with a long right-hand tail. After logarithmic transformation, the frequency distribution fitted closer to a normal distribution than did the original EC50 values. The preventive efficacies of trifloxystrobin at 5, 15, and 45 μg/mL were 71.4%, 96.5%, and 100.0%, respectively, while the curative efficacies were 40.6%, 48.7%, and 73.4%, respectively. Both preventive and curative efficacies of trifloxystrobin at 45 μg/mL were significantly higher (P ≤ 0.046) than those of the reference fungicide carbendazim. Assays with six arbitrarily selected isolates demonstrated that salicylhydroxamic acid (SHAM) at 20 μg/mL reduced trifloxystrobin EC50 values by 84.0% on average and greatly potentiated efficacy of trifloxystrobin. The average co-toxicity factor of SHAM and trifloxystrobin for preventive efficacy was 64.3, indicating considerable synergisms in planta. Hence, SHAM should not be included in in vitro assay of S. sclerotiorum sensitivity to trifloxystrobin.  相似文献   

8.
Frogeye leaf spot, caused by Cercospora sojina, causes yield reductions to soybean (Glycine max) grown worldwide. Quinone outside inhibitor (QoI) fungicides have been effective in managing frogeye leaf spot, but the risk of selecting C. sojina strains with resistance to this class of fungicides is considered high. A QoI fungicide resistance monitoring program was initiated, in which sensitivities to azoxystrobin, pyraclostrobin, and trifloxystrobin were determined in C. sojina isolates collected prior to QoI fungicide use on soybean (baseline group) and C. sojina isolates collected from soybean fields in 2007, 2008 and 2009. For the baseline group, the mean effective fungicide concentration at which 50% of the conidial germination was inhibited (EC50) was determined to be 0.01287, 0.00028 and 0.00116 μg ml−1 for azoxystrobin, pyraclostrobin and trifloxystrobin, respectively. When mean EC50 values of 2007, 2008 and 2009 C. sojina isolates were compared to baseline C. sojina EC50 values, a small but statistically significant (P ≤ 0.05) shift towards less sensitivity was observed for trifloxystrobin in 2009. Although small (<1.5-fold), this shift in sensitivity indicates a risk of selecting for C. sojina strains with reduced sensitivity to QoI fungicides, and fungicide sensitivities should continue to be monitored in the future.  相似文献   

9.
Alternaria late blight (ALB) caused by Alternaria spp. is an annual production concern for pistachio growers in California. In this study, isolates of Alternaria alternata collected from California pistachio orchards between 1998 and 2003 (population A, n = 46) and in 2010 (population B, n = 38) prior to the registration and use of sterol demethylation-inhibiting (DMI) fungicides for ALB control, were tested for their sensitivity to difenoconazole, propiconazole, and tebuconazole using an in vitro mycelial growth assay. The 50% effective dose (EC50) values for isolates in population A to difenoconazole, propiconazole, and tebuconazole, respectively, ranged from 0.02 to 0.82 μg/mL (mean = 0.17), 0.25–5.73 μg/mL (mean = 1.29), and 0.02–2.76 μg/mL (mean = 0.96), and from 0.02 to 0.93 μg/mL (mean = 0.21), 0.13–5.36 μg/mL (mean = 1.25), and 0.17–5.47 μg/mL (mean = 1.03) for those in population B. Among 65 isolates collected in 2012 from orchards with very limited exposure to difenoconazole, propiconazole or metconazole (population C, n = 65), the EC50 values for tebuconazole ranged from 0.02 to 2.99 μg/mL (mean = 0.51), while EC50 values for difenoconazole of 55 of these isolates varied from 0.01 to 0.44 μg/mL (mean = 0.06). The DMI-exposed population C was found to be on average two to four times less sensitive compared with the populations A and B. Pearson correlation analyses of EC50 values for the three fungicides showed significant positive correlations between the sensitivities of tebuconazole and propiconazole (P < 0.01, r = 0.32), tebuconazole and difenoconazole (P < 0.01, r = 0.26), and difenoconazole and propiconazole (P < 0.01, r = 0.40). Results indicate a clear difference in fungicide intrinsic activity, with difenoconazole being more active than the two other DMIs. Although wide variations in sensitivities for tebuconazole and propiconazole were observed in the non- and DMI-exposed Alternaria populations, efficacy of DMI products has been excellent against ALB. The data collected here will be crucial for the rational use of DMIs in fungicide spray programs for ALB management and serve as a reference to detect any shifts in A. alternata sensitivity to these fungicides in subsequent years as they become more frequently used in California pistachios.  相似文献   

10.
Peach brown rot is a severe disease caused by ascomycete fungus Monilinia fructicola and is primarily controlled by chemical fungicides. However, the utilization of fungicides has caused many problems such as microbial resistance, environmental pollution, and fruit contamination. The growing concern for food safety requires alternative management methods that are safe to humans and benign to the environment. Here we report that the extract from Coptis chinensis (a Chinese herb named “Huang Lian”) demonstrates a strong inhibition to M. fructicola. The 50% effective concentration (EC50) of C. chinensis extract to M. fructicola was only 0.91 mg/mL, while the EC50s to other fungi such as Botrytis cinerea and Alternaria solani were 14.09 mg/mL and 27.35 mg/mL, respectively. These results indicate that the extract of C. chinensis has a specific inhibition to M. fructicola. Subsequent partitioning of the ingredients in C. chinensis extract revealed that berberine, the conventional anti-bacterial alkaloid, was the predominant ingredient that exerted robust inhibition against M. fructicola. The EC50 and minimum inhibitory concentration (MIC) against M. fructicola were as low as 4.5 μg/mL and 46.9 μg/mL, respectively. Compared to berberine’s analogs in C. chinensis such as palmatine, berberine tannate and jatrorrhizine, berberine showed the strongest inhibition against M. fructicola. This finding provided insight into the structure–activity relationship between berberine and its analogs. Notably, not only can berberine prevent spore germination and hyphal growth, it also inhibits the activity of cutinase secreted by M. fructicola, implying the potential function of berberine in reducing the pathogenesis of M. fructicola. In addition, the strong in vivo inhibition of berberine against M. fructicola was observed with no visual cytotoxicity noted to peach fruits, even at berberine concentration of 400 μg/mL. Note that this was much higher than its MIC value (46.90 μg/mL). Overall berberine, as a natural compound, may be a promising candidate in control of brown rot.  相似文献   

11.
The study deals with evaluation of antifungal and antiaflatoxigenic Caesulia axillaris Roxb. essential oil (EO) against herbal raw materials deteriorating fungi and its free radical scavenging activity. During mycoflora analysis these herbal raw materials were found to be severely contaminated by different fungi and aflatoxins. A total of nine different fungal species were isolated from three herbal raw materials. Aspergillus flavus LHPtc was recorded as the highest aflatoxin B1 producing strain. EOs of some plants were tested for their fungitoxicity against the toxigenic strain A. flavus LHPtc, and C. axillaris EO was found as potent fungitoxicant. C. axillaris EO was chemically characterized through GC-MS analysis which depicted the presence of 18 compounds, dl-limonene and Euasarone being the major components. The EO exhibited broad spectrum of fungitoxicity against fungi causing postharvest deterioration of herbal raw materials. At 1.0 μl ml−1 the oil showed complete inhibition of fungal growth and aflatoxin B1 production was inhibited at 0.8 μl ml−1. Free radical scavenging activity of the oil was also recorded by 2,2-diphenyl-1-picrylhydrazyl assay, and its IC50 value was found 18 μl ml−1. The safety limit of the EO was determined in terms of LD50 on mice, which was 9166.6 μl kg−1, suggesting its non mammalian toxicity. The EO of C. axillaris may be recommended as a plant based preservative in enhancement of shelf life of herbal raw materials by preventing their lipid peroxidation as well as biodeterioration due to fungal and aflatoxin contamination.  相似文献   

12.
The white rot disease caused by Botryosphaeria dothidea threatens apple production in Bohai bay area and along the Yellow River of China, where disease control is largely dependent on fungicides such as tebuconazole. A total of 146 isolates of B. dothidea obtained from different apple orchards in six provinces were tested for their sensitivity to tebuconazole, carbendazim and iprodione. The EC50 values of all tested isolates for tebuconazole were from 0.035 to 1.415 μg/mL. The broad range of EC50 values of tebuconazole suggests an obvious variation among the 146 isolates. Isolate HB13 (EC50 = 1.415 μg/mL) showed reduced sensitivity to tebuconazole, with an EC50 value significantly higher than those of the other 145 isolates tested. The low sensitivity of HB13 was stable after 15 generations, and this isolate showed similar pathogenicity as susceptible strains. EC50 correlation analysis indicates no cross resistance between tebuconazole and carbendazim and iprodione. Field efficacy trials showed that tebuconazole remains very effective for apple white rot control in China.  相似文献   

13.
In recent years the strawberry tree (Arbutus unedo L.) is being gradually replaced by other species with higher economic value. With the ultimate goal of selecting superior genotypes, the present work was initiated to study the antioxidant and antimicrobial activities, and total phenolic content in 19 different genotypes of A. unedo leaves from the Trás-os-Montes region of Portugal.The genotype Bragança 1 contains higher total phenolic content (215.0 mg GAE/gextract) whereas the Vila Boa 4 genotype shows lower total phenolic content (148.0 mg GAE/gextract). In both methods tested to evaluate the antioxidant activity, Vila Verde and Donai displayed the highest antioxidant capacity (EC50 values of 0.088 and 0.090 mg/mL, respectively, for DPPH; EC50 values of 0.233 and 0.245 mg/mL, respectively, for reducing power assay) while Vila Boa 2 reported the lowest antioxidant potential (EC50 values of 0.142 and 0.378 mg/mL, respectively, in DPPH and reducing power methods). Linear negative correlations were established between the total phenol contents and the EC50 values for both of the antioxidant activity methods tested. Preliminary assays for antimicrobial potential showed that extracts from A. unedo leaves display antibacterial activity, with MIC values of 1 and 5 mg/mL for some Gram-positive and Gram-negative bacteria, respectively. Taken together, the results suggest that A. unedo leaves are a potential source of natural compounds with valuable bioactive properties that could be explored by the pharmaceutical, chemical and food industries.  相似文献   

14.
Tobacco black shank caused by Phytophthora parasitica is a devastating soil-borne disease of tobacco in China. Control of tobacco black shank relies on numerous fungicide applications. A new carboxylic acid amide (CAA) fungicide, mandipropamid, was examined for its effects on various asexual developmental stages of P. parasitica in vitro and in tobacco seedlings. Although mandipropamid did not affect discharge of zoospores from sporangia, it strongly inhibited mycelial growth (mean EC50 value of 0.0112 μg ml−1), sporangia production (mean EC50 value of 0.009 μg ml−1), germination of encysted zoospores (mean EC50 value of 0.014 μg ml−1), and germination of sporangia (mean EC50 value of 0.017 μg ml−1). For protective activity in tobacco seedlings, various applications of mandipropamid were superior in reducing black shank compared to that of metalaxyl and of azoxystrobin; while for curative activity assay, 100 μg ml−1 of mandipropamid exhibited the same efficacy as that of metalaxyl, and presented superior activity than that of azoxystrobin. In 2010 and 2011, 119 isolates of P. parasitica from Guizhou Province of China were characterized for the baseline sensitivity to mandipropamid by measuring mycelial growth. Values of effective concentrations for 50% mycelia growth inhibition varied from 0.0068 to 0.0285 μg ml−1 and averaged 0.013 (±0.0045) μg ml−1, with a unimodal distribution. This information will serve as a baseline for tracking future changes in sensitivities of P. parasitica populations to mandipropamid in China.  相似文献   

15.
Elicitors of systemic acquired resistance are well known to reduce severity of several plant pathogenic diseases caused by fungi, bacteria and viruses. Their field applications for management of plant diseases are, however, limited because of yield penalties. Our studies on affect of Benzo (1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH), an elicitor of systemic acquired resistance, on chickpea blight caused by a fungal pathogen Didymella rabiei showed that multiple foliar applications of the chemical were effective in management of the disease under economic threshold levels. Multiple applications, however, affected chickpea grain yield adversely. The BTH induced yield penalties could be prevented by foliar spray schedule comprised of BTH and a contact fungicide mancozeb. One spray of BTH (50 ppm) followed by another of mancozeb (0.2%) was less effective (8.3% severity) than three sprays of BTH (4.2% severity) in blight control, however, this treatment enhanced grain yield significantly (1.241 t ha−1) over three sprays of BTH (0.922 t ha−1).  相似文献   

16.
Organophosphate and carbamate insecticides exert their neurotoxic effects by inhibiting acetylcholinesterase (AChE), thereby, prolonging the action of acetylcholine at cholinergic synapses, resulting in neuronal hyperexcitation. Mutations at the AChE target site confer modified acetylcholinesterase (MACE) phenotypes. Target-site insensitivity of AChE was characterized in field-collected, tobacco-adapted forms of the green peach aphid, Myzus persicae (Sulzer), from nine different states in the eastern United States from 2004 to 2007. The specific activity of the AChE among the 65 aphid colonies screened by Ellman's assay ranged from 0.017–0.259 U/min/mg protein. Eight colonies, with a wide range of specific activities were chosen to study the inhibition of AChE in the presence of two carbamate insecticides, methomyl and pirimicarb. IC50 values for methomyl ranged from 0.35 to 2.4 μM, while six out of eight colonies had lower values that ranged from 0.16 to 0.30 μM for pirimicarb. Two colonies that were inhibited by methomyl had very high IC50 values for pirimicarb, 40.4 and 98.6 μM respectively. The target-site insensitivity in these two colonies that are resistant to pirimicarb could be due to an ace2 gene mutation. This is the first instance where MACE phenotypes in M. persicae from the United States were studied and confirmed. The results indicate that the possible insensitivity due to MACE resistance in some colonies may render selected carbamate insecticides ineffective. Concerns of MACE resistance in managing the tobacco-adapted form of the green peach aphid on tobacco in the United States are discussed.  相似文献   

17.
The efficacy of a new fungicide fluopicolide in suppression of Phytophthora blight caused by Phytophthora capsici was evaluated under laboratory and field conditions. Studies with 51 P. capsici isolates from vegetable crops in Georgia, USA, indicated that 5.9% of the isolates were resistant, 19.6% were intermediately sensitive, and 74.5% were sensitive to 100 μg ml−1 of mefenoxam based on in vitro mycelial growth. EC50 values of fluopicolide in inhibiting mycelial growth of 25 isolates, representing resistant, intermediately sensitive, and sensitive to mefenoxam, ranged from 0.05 to 0.35 μg ml−1 with an average of 0.2 μg ml−1 EC50 values of fluopicolide in suppressing zoospore germination and sporangium production of the 25 isolates ranged from 1.1 to 4.5 μg ml−1 and 0.3–9.0 μg ml−1, respectively. Evaluation of a collection of 150 P. capsici isolates from vegetables and irrigation ponds found none of the isolates were resistant to 10 μg ml−1 of fluopicolide. Field experiments were conducted to determine the efficacy and application methods of fluopicolide for control of P. capsici on squash in spring 2007 and 2009. Fluopicolide applied through drip irrigation or as a foliar spray at 86.6 or 115.4 g ha−1 consistently provided significant disease reduction and increased squash yield. Results with fluopicolide were similar or slightly superior to mefenoxam applied at recommended rate. Fluopicolide applied at 57.7 g ha−1 did not provide consistent satisfactory disease suppression. The results indicated that fluopicolide was effective in suppression of different stages of the life cycle of P. capsici and could be a viable alternative to mefenoxam for managing Phytophthora blight in squash production.  相似文献   

18.
In the UK, two demethylation inhibitor (DMI) fungicides, myclobutanil and fenbuconazole, are recommended for controlling apple scab. Experiments were conducted to determine whether the sensitivity of V. inaequalis to myclobutanil was correlated with that to fenbuconazole. There was a marked reduction in the sensitivity of V. inaequalis to myclobutanil; averaged ED50 values increased from 0.338 mg L−1 in the baseline population to 2.945 mg L−1 for isolates from a commercial orchard. Overall, the average ED50 value for fenbuconazole was only about 20% of that for myclobutanil for the baseline population. There was an overall significant positive correlation in the fungal sensitivities to myclobutanil and fenbuconazole, but such correlation only accounted for 40% of the total observed variability. In addition, the magnitude of this cross-resistance varied among orchards. The finding is discussed in the context of fungicide deposition in relation to disease control.  相似文献   

19.
The economics of fungicide use in winter wheat in southern Sweden   总被引：1，自引：0，他引：1  
In southern Sweden, fungicide treatment of winter wheat is prevalent and recommended almost routinely against leaf blotch diseases. However, yield increases and hence the resulting net returns from fungicide use are highly variable within and between years. These variations raise questions about whether, when and how fungicides should be used. To help answer these questions, a thorough economic evaluation of fungicide use was carried out, based on results from untreated plots and fungicide-treated plots in trials in farmers' fields, 1983–2007. Scenarios with varying grain prices and costs of fungicide treatment were evaluated and examined. Doubling and tripling the grain price led to the largest impact on the net return from fungicide treatment, followed by increasing cost of the fungicide. Other costs were of minor importance. The mean net return from fungicide use was no more than 12 € ha−1 over the 25 years (2008 grain prices and costs used in calculations). Furthermore, the mean net return was negative in 10 years and less than 50% of the entries were profitable to treat in 11 years. Changes over time and changes in controllable factors (e.g. fungicide and cultivar choice, crop rotation, techniques) and uncontrollable factors (e.g. emerging and new diseases, price relations) influenced the profitability of fungicide use. Fungicide use was in fact more profitable (mean net return 21 compared with 3 € ha−1) during the latter part of the period (1995–2007) than in the earlier part (1983–1994). Improved decision support systems in a holistic framework based on sound economics are urgently needed.  相似文献   

20.
Some secondary metabolites of plants function as antimicrobial products against phytopathogens and constitute an increasingly important class of pesticides. In the present study, the essential oil of Asarum heterotropoides var. mandshuricum was analyzed by GC/MS and its antimicrobial activity was evaluated against five phytopathogenic fungi. Major components of the oil were methyleugenol (59.42%), eucarvone (24.10%), 5-allyl-1,2,3-trimethoxybenzene (5.72%), and 3,7,7-trimethylbicyclo(4.1.0)hept-3-ene (4.93%). The essential oil and the most abundant component, methyleugenol, were separately assayed for inhibition of 5 pathogens: Alternaria humicola, Colletotrichum gloeosporioides, Rhizoctonia solani, Phytophthora cactorum and Fusarium solani. Both the oil and methyleugenol strongly inhibited the growth of the test pathogens (IC50 values <0.42 μg ml−1) except F. solani, with the best activity against P. cactorum (IC50 values = 0.073 and 0.052 μg ml−1, respectively). It is concluded that the essential oil of A. heterotropoides var. mandshuricum has a broad antiphytopathogenic spectrum, and that methyleugenol is largely responsible for the bioactivity of the oil. The mode of action of methyleugenol against P. cactorum is discussed based on changes in the mycelial ultrastructure.  相似文献   

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