Screening Of Fungicides Research Articles

Synthesis, Crystal Structure, and Biological Activity of 4-Methyl-1,2,3-thiadiazole-Containing 1,2,4-Triazolo[3,4-b][1,3,4]thiadiazoles

Heterocyclic compounds play an important role as the main sources of lead molecules of agrochemicals. Synthesis and biological activity of thiadiazole-containing 1,2,4-triazolo[3,4-b][1,3,4]-thiadiazoles were seldom reported. To find novel lead compounds with various biological activities, a series of 6-substituted-3-(4-methyl-1,2,3-thiadiazolyl)[1,2,4]triazolo[3,4-b][1,3,4]thiadizoles were rationally designed and synthesized according to the principle of combinations of bioactive substructures by the condensation of 3-(4-methyl-1,2,3-thiadiazolyl)-4-amino-1,2,4-triazole-5-thione with various carboxylic acids and phosphorus oxychloride. All newly synthesized compounds were identified by proton nuclear magnetic resonance ((1)H NMR), infrared spectroscopy (IR), electroionization mass spectrometry (EI/MS), and elementary analysis. The crystal structure of 3-(4-methyl-1,2,3-thiadiazolyl)-6-(4-methylphenyl)[1,2,4]triazolo[3,4-b][1,3,4]thiadizole was determined by X-ray diffraction crystallography. In this crystal, two intermolecular hydrogen bonds (N2...H-C12 and N3...H-C13), a weak intermolecular interaction (S...S), and the weak ppi-ppi intermolecular interaction were observed. Fungicide screening indicated that all of the target compounds showed certain extent of growth inhibition against fungi tested. 3-(4-Methyl-1,2,3-thiadiazolyl)-6-n-propyl[1,2,4]triazolo[3,4-b][1,3,4]thiadizole and 3-(4-methyl-1,2,3-thiadiazolyl)-6-trichloromethyl[1,2,4]triazolo[3,4-b][1,3,4]thiadizole were found to have potential wide spectrum of fungicide activity. The median effective concentrations (EC(50)) detected for 3-(4-methyl-1,2,3-thiadiazolyl)-6-trichloromethyl[1,2,4]triazolo[3,4-b][1,3,4]thiadizole to six fungi were from 7.28 micromol/L against Pellicularia sasakii (Shirai) to 42.49 micromol/L against Alternaria solani . The results indicated that thiadiazole-containing 1,2,4-triazolo[3,4-b][1,3,4]-thiadiazoles were potential fungicide lead compounds.

Genetic analysis of Mycosphaerella fijiensis in the Ugandan Lake Victoria region

A collection of Mycosphaerella fijiensis, in total 71 isolates from 11 countries, of which 54 isolates were derived from the Ugandan Lake Victoria region, were analysed with regard to molecular markers and benomyl resistance to characterize the population structure. Forty‐seven alleles from seven restriction fragment length polymorphism (PCR‐RFLP) and five microsatellite markers were scored and utilized in the study. Using analysis of molecular variance (amova), no significant genetic differentiation could be found between isolates from different leaves compared to isolates from a single leaf (P = 0·07). Exact tests of the allelic frequencies revealed no differences between isolates from different districts or between single‐leaf‐derived isolates compared to isolates derived from different leaves (P > 0·05 in all cases except two, which, however, were shown to be of type‐I error). Resistance to benomyl, analysed both by PCR and fungicide screening, revealed that all isolates were susceptible. Compiled information from the various datasets implied that the Ugandan M. fijiensis population in the Lake Victoria Basin constitutes a homogenous population, probably as the result of a recent founder event.

In Vitro Screening of Fungicides to Control Artillery Fungi

Abstract We evaluated the influence of 26 fungicides at four different concentrations (0.1, 1.0, 10.0, and 100.0 a.i.) on in vitro growth of an artillery fungus (Sphaerobolus stellatus isolate SS8) in Petri plate culture. The most effective fungicides, as determined by comparison of mean EC50 values, were polyoxin-D and azoxystrobin, followed by pyraclostrobin, triademifon, tebuconazole, propiconazole, thiophante-methyl, triticonazole, thiram, and fludioxonil. These in vitro laboratory findings need to be evaluated in the field before specific fungicides can be recommended to control artillery fungi in landscape mulch.

The PsCZF1 gene encoding a C 2H 2 zinc finger protein is required for growth, development and pathogenesis in Phytophthora sojae

The C 2H 2 zinc finger proteins form one of the largest families of transcriptional regulators in eukaryotes. We identified a Phytophthora sojae C 2H 2 zinc finger ( PsCZF1), that is highly conserved in sequenced oomycete pathogens. In transformants of P. sojae containing the PsCZF1 promoter fused to the β-glucuronidase (GUS) reporter gene, GUS activity was highly induced in the P. sojae oospore stage and upregulated after infection. To elucidate the function of PsCZF1, its expression was silenced by introducing anti-sense constructs into P sojae. PsCZF1-silenced transformants did not exhibit altered cell size or morphology of sporangia and hyphae; however, hyphal growth rate was reduced by around 50% in the mutants. PsCZF1-deficient mutants were also impaired in production of oospores, swimming zoospores and germinating cysts, indicating that the gene is involved in various stages of the life cycle. Furthermore, we found that PsCZF1-deficient mutants lost virulence on host soybean cultivars. Our results suggest that this oomycete-specific C 2H 2-type zinc finger protein plays an important role in growth, development, and pathogenesis; therefore, PsCZF1 might be an attractive oomycete-specific target for chemical fungicide screening.

In vitro screening of systemic fungicides against Phomopsis azadirachtae, the incitant of die-back of neem

Phomopsis azadirachtae Sateesh, Bhat & Devaki is the causal organism of die-back of neem (Azadirachta indica A.Juss.) which is, presently, a major crippling disease of neem in India. Six systemic fungicides such as Bavistin (carbendazim), Contaf (hexaconazole), Beam (tricyclazole), Fuji-one (isoprothiolane) Roko (thiophanate methyl) and Downymil (metalaxyl) were evaluated against P. azadirachtae under in vitro conditions. Colony diameter, mycelial dry weight, pycnidial formation and the germ tube length of the pathogen were the parameters studied. The results indicated that carbendazim was the most effective in inhibiting the growth followed by thiophanate methyl. Among the different concentrations tested, carbendazim at 0.25 ppm and thiophanate methyl at 0.75 ppm were optimum for controlling the growth of the pathogen. Both these fungicides can be utilized for the control of die-back of neem.

Developing Common Spray Schedules for Pest Control with Combination of Pesticides and Fungicides under Mixed Conditions of Apple and Pear Orchards 1. Screening of Fungicides and Examining Efficacy of Spray Schedules for Control of Pear Ring Rot Caused by Botryosphaeria berengeriana

Developing Common Spray Schedules for Pest Control with Combination of Pesticides and Fungicides under Mixed Conditions of Apple and Pear Orchards 1. Screening of Fungicides and Examining Efficacy of Spray Schedules for Control of Pear Ring Rot Caused by <i>Botryosphaeria berengeriana</i>

Application of Binding Spectrum in DMIs Fungicide Screening

In order to establish a fast and accurate method for novel DMIs fungicide screening, lanosterol 14α-demethylase of Magnaporthe grisea expressed in E. coli was used as target enzyme and the DMI fungicides diniconazole, tebuconazole, triadimenol and triadimefon were used as representative fungicides, the effects of enzyme activity, enzyme purity and concentration on the binding spectra were investigated. The results showed that active enzyme, elimination of interference of other P-450s and proper enzyme concentration were necessary for obtaining accurate binding spectra. The K d values of diniconazole, tebuconazole, triadimenol and triadimefon were 0.143 μmol/L, 0.24 μmol/L, 0.257 μmol/L and 0.307 μmol/L respectively, which significantly correlated to their 120h-EC 50 values on the growth of M.grisea. The results indicated that the binding spectra of fungicide and lanosterol 14α-demethylase can serve as a reliable and fast method for novel fungicide screening.

Screening of fungicides which are used around transplanting stage for the rice blast fungus (Magnaporthe grisea)

Screening of fungicides which are used around transplanting stage for the rice blast fungus (Magnaporthe grisea)

SUCCESSFUL MANAGEMENT OF COLLETOTRICHUM CROWN AND STOLON ROT IN RUNNER PRODUCTION IN SUB-TROPICAL AUSTRALIA

Crown, stolon, and petiole rots caused by Colletotrichum gloeosporioides (C.g.) were first identified in runner beds of the Queensland Approved Runner Scheme (QARS) in February 1989. The outbreaks occurred annually from 1990 to 1994. Minor losses in subsequent fruit crops occurred from 1990 to 1993, with 50% post-establishment losses occurring on fruit farms in southeast Queensland in 1994. The objective of this work was to provide a control strategy for the disease that would give stability to the QARS. Runner-bed trials in 1993-1994 showed that Octave® (462 g/kg prochloraz as the MnCl2 complex) was highly effective in reducing the incidence field symptoms and laboratory recovery of C.g. from symptomless petioles. A simple detached petiole laboratory test for measuring fungicide efficacy in runner bed trials and for laboratory screening of fungicides, is described. Scheme protocols were changed to require that only foundation plants from tissue culture were allowed onto QARS sites. These were to be symptomless and to have tested negative for the presence of C.g. The application of Octave® at fortnightly intervals in all QARS nurseries has reduced the level of visible symptoms and the laboratory recovery of C.g. from symptomless petioles to almost zero.

Screening of Fungicides for Control of Sweet Cherry Black Spot Caused by Alternaria sp.

Screening of Fungicides for Control of Sweet Cherry Black Spot Caused by <I>Alternaria</I> sp.

Fungicidal meta-Substituted Strobilurin Analogs

Strobilurin analogs in which the side chain is in a meta-relationship to the pharmacophore are active fungicides provided an ortho-group is also present. Syntheses, fungicidal screening results and structure–activity relationships for these compounds are described. A new pharmacophore synthesis from aniline precursors is also detailed.

Laboratory, Greenhouse, and Field Assessment of Fourteen Fungicides for Activity Against Claviceps africana, Causal Agent of Sorghum Ergot.

Commercial formulations of 14 fungicides representing seven chemical classes were assessed in vitro and in vivo for activity against Claviceps africana, causal agent of sorghum ergot. All fungicides markedly reduced spore germination in vitro on water agar, with effective concentration (EC)50 values (based on active ingredient) that ranged from 0.01 μg ml-1 for thiophanatemethyl and trifloxystrobin to 1.18 μg ml-1 for cyprodinil. In vivo assays included applications of fungicide on full bloom panicles of a male-sterile line, ATx623, and then inoculating panicles with a conidial suspension immediately after the fungicide had dried. In greenhouse trials and in the 2000 field evaluation, a single application of propiconazole, tebuconazole, triadimefon, myclobutanil, or azoxystrobin at a rate of 25 μg ml-1 markedly suppressed ergot severity on ATx623. In the 2001 field evaluation, tebuconazole applied at 25 μg ml-1 was most effective in reducing levels of ergot severity. Ergot control was greater when fungicides were applied at 25 μg ml-1 than at 5 μg ml-1. Generally, triazole and strobilurin classes of fungicide were more effective in controlling ergot than benzimidazole, anilinopyrimidine, ethylenebisdithiocar-bamate (EBDC), pyridinamine, and organometallic classes. At the two fungicide rates used in this study, ergot severity increased between 7 and 10 days after inoculation. Results showed that in vitro fungicide screening by measuring spore germination inhibition was not a good predictor of performance in the field. Results from the field trials suggest that control, particularly under ergot-favorable environments, may require higher rates than used in this study.

SEMI-SELECTIVE MEDIUM FOR ISOLATION OF COLLETOTRICHUM GLOEOSPORIOIDES FROM SOIL

Isolation of Colletotrichum gloeosporioides (causal agent of yam anthracnose) from soil is difficult because of the presence of fast growing micro-organisms like Rhizoctonia spp., Rhizopus spp., Penicillium spp. and bacteria. Therefore, a semi-selective medium consisting of antimicrobial agents such as pencycuron 50 mg L−1, tolclofos-methyl 10 mg L−1, streptomycin sulphate 100 mg L−1, chloramphenicol 100 mg L−1 and chlortetracycline 100 mg L−1 was developed using potato dextrose agar as the basal medium. The procedure involved screening of candidate fungicides, developing a suitable combination of antimicrobial agents, assessing the proposed semi-selective medium and adjustment of pH of the medium to 5. The effectiveness of the medium is due to selective inhibition of micro-organisms by the antimicrobial agents and the development of distinct salmon-pink colonies of C. gloeosporioides.

In vitro screening and evaluation of fungicides for the control of Claviceps africana on sorghum seed

Eleven fungicides, benomyl, bitertanol, captan, carbendazim, mancozeb, procymidone, propiconazole, tebuconazole, thiram, triadimenol and tridemorph, were tested in vitro at 50 and 10 mg a.i./L for their effects on the macroconidial germination of Claviceps africana, the sorghum ergot pathogen. Thiram and captan completely inhibited conidial germination of the two isolates (UQE1 and UQE2) tested. Nine of the best fungicides from this test were selected for assessment as seed treatments using sorghum seed which had been artificially coated with ergot honeydew containing macroconidia of the isolates UQEl or UQE9. Captan and thiram at 0.5, 1 and 2 g a.i./kg seed completely inhibited macroconidium germination of one isolate and reduced germination of the other to <0.2%. Thiram applied to honeydew-coated sorghum seed completely inhibited macroconidium germination at a rate lower than that currently registered (2.4 g a.i./kg) for use on sorghum seed in Australia. These results have important implications for the movement of sorghum seed from areas where C. africana is endemic to areas which are free from the pathogen.

Septoria Leaf Spot of Stevia rebaudiana in Canada and Methods for Screening for Resistance

The herb Stevia rebaudiana is a potential source of low‐calorie sweeteners. In 1995, a severe leaf spot and blight was observed in stevia production fields and research plots in the provinces of Ontario and British Columbia, Canada. The disease was characterized by angular, shiny, olive‐grey lesions that rapidly coalesced and were often surrounded by a chlorotic halo. Leaves quickly became necrotic and often dropped off the plant. The disease progressed upwards in the foliage during the growing season. A Septoria sp. was isolated from diseased leaves. Ten isolates (five from each of the two provinces) of the Septoria sp. were compared with respect to conidial size. Across isolates, conidia lengths and widths overlapped (grand means for length and width were 71.4 μm and 1.4 μm, respectively). Conidiogenesis was holoblastic. Morphological characteristics and disease symptoms were similar to those of Septoria steviae, previously reported only from Japan. It was concluded that the Canadian isolates belonged to S. steviae. Isolates from Canada did not differ significantly from one another with respect to effects of temperature on colony growth or germination of conidia. Optimum temperatures for these parameters were between 20 and 25°C. In field trials, the pathogen was shown to successfully over‐winter in diseased leaf tissue. In order to develop procedures for identification of resistant germplasm and greenhouse screening of candidate fungicides, effects of leaf wetness period, inoculum concentration, and plant age on disease development were determined. Thirty‐six hours of leaf wetness were required for consistent development of leaf spots. Inoculum concentrations of 5 × 105 conidia/ml or more were required to produce high disease severities; 6‐week‐old plants were more susceptible than older plants. In the growth chamber, greenhouse, and field trials, germplasm selections with high levels of resistance to S. steviae were identified. This is the first report of resistance to this disease in S. rebaudiana.

Evaluation of Fungicides and Surfactants for Control of Fairy Rings Caused by Marasmius oreades (Bolt ex. Fr.) Fr.

Marasmius oreades, a causal agent of fairy rings, is one of the most important pathogens of turfgrass in the Great Plains region of North America. Following in vitro and greenhouse screening of surfactants and fungicides, two organosilicone surfactants, Silwet L-77 and Sylgard, together with the fungicide chlorothalonil, were evaluated in the field. Treatments were applied to healthy and infested turfgrass (Poa pratensis L., Festuca rubra L.) in either 1992, 1993, or in both years. Plots were sampled for grass production, canopy cover, mushroom production, grass chlorophyll content, soil water content, and phytotoxicity. Typically, there were no significant fungicide effects, fungicide by surfactant interactions or differences between Silwet L-77 and Sylgard. Relative to the water control, surfactants caused an approximate 3-fold increase in grass productivity on infested plots in the year of application. However, the difference in canopy cover between organosilicone-treated and control plots tended to be much less. Applying the surfactants to diseased plots in two successive years decreased the canopy cover but had no significant effect on grass production. Chlorophyll content tended to decrease in response to surfactants regardless of whether the turf was infested or healthy. Surfactants almost completely eliminated mushroom production and greatly reduced the occurrence of mycelium. Both organosilicones increased soil water content in infested areas; differences were detectable 2 years after application. Acute phytotoxicity from the surfactants was detected in infested but not in healthy plots. There was no direct evidence of chronic phytotoxicity. Organosilicone surfactants appear to have considerable potential for the management of fairy rings. Chemical names used: oxyalkylenemethylsiloxane (Silwet L-77); 2-(3-hydroxypropyl)-heptamethyltrisiloxane (Sylgard); tetrachloroisopthalonitrile (chlorothalonil).

The repression and stimulation of growth of Erysiphe sp. on Rhododendron by fungicidal compounds

Erysiphe sp. is a causal agent of powdery mildew on Rhododendron. A novel in vivo method permitting the screening of fungicides on woody plants is described. Eight fungicides were evaluated for activity against Erysiphe sp. using Rhododendron ponticum microplantlets grown in vitro. Pathogen development changed with both the type of fungicidal compound and the concentrations applied. The most active materials were fenpropidin and penconazole, which showed high activity at the lowest concentrations. Six of the compounds performed more effectively than a mixture of bupirimate + triforine (Nimrod T), the standard recommendation for control of this pathogen on Rhododendron. All fungicides affected the sporulation of Erysiphe sp., with propiconazole, pyrazophos and triadimenol causing a significant increase in sporulation at the lowest concentrations. At higher concentrations, sporulation was significantly reduced by all treatments. No phytotoxic effects were detected with any fungicide at any concentration. The growth of plantlets in most treatments showed no significant difference from the untreated controls. The results of the study are discussed in relation to strategies for control and the epidemiology of Erysiphe sp. infecting Rhododendron.

A Simple and Reliable Method for Evaluating the Effectiveness of Fungicides for Control of Powdery Mildew(Sphaerotheca macularis) on Strawberry.

A simple and reliable method was established for evaluating fungicide efficacy in the control of strawberry powdery mildew. The lower surface of newly developed leaflets of strawberry runner-tip plantlets was the best for assay inoculation, and disease severity could be visually evaluated with ease 7 days after inoculation. The youngest leaflets were more susceptible than the intermediate leaflets, and the oldest leaflets were hardly infected by the fungus. The colonies on the inoculated lower surface of runner-tip plantlets were observed clearly 7 days after inoculation and remained alive for 28 days. Disease severity was consistently high when sprayed with conidial suspension containing more than 5.0×104 conidia/ml. Maximum infection of inoculated leaflets was observed when incubated at near 20°C. Infection frequency at 15°C was greater than at 25°C. No disease development was observed at or above 30°C. When leaflets were sprayed with effective fungicides before inoculation, disease development was remarkably suppressed. The effects of fungicide were more clearly evaluated with leaflets in test tubes than those on whole plants in the vinyl-covered house. These results indicate the validity of this method for the accurate evaluating of fungicide effectiveness. This method will be adapted to the screening of fungicides for powdery mildew control.

In vitroevaluation of fungicides against clove isolate ofCylindrocladium quinqueseptatumin Sri Lanka

Cylindrocladium quinqueseptatum is identified as a serious pathogen of Eugenia caryophyllata and a potential pathogen of Hevea brasiliensis in Sri Lanka. A total of 16 fungicides were screened against C. quinqueseptatum employing three screening techniques; conidial germination test (CGT), poisoned food technique (PFT), and soil fungicide screening test (SFST) to evaluate respectively, the efficacy of inhibiting conidial germination and mycelial growth and rendering microsclerotia non‐viable. Eight fungicides (benomyl, captan, chlorothalonil, mancozeb, metalaxyl 8% + mancozeb 64%, propineb, propineb 56% + oxadixyl 10% and thiram) were found to be effective in inhibiting conidial germination 100% (EC 100) at a very low concentration of 25 μg/ml. Three more fungicides, viz. oxadixyl 10% + mancozeb 56%, tebuconazole, and copper oxychloride achieved EC 100 in the same test at 100μg/ml, 200 μg/ml and 800 μg/ml respectively. However, only six fungicides, namely benomyl (EC 100 = 50 μg/ml), copperoxychloride (EC...

Management measures to control foot rot of sweet potato caused byPlenodomus destruens

Abstract The effect of planting stem cuttings infected with Plenodomus destruens on the stand, the varietal disease resistance, the effect of the position of the cutting on the vine as related to disease incidence, and a fungicide screening for stem‐cutting treatment were studied at EMBRAPA/CNPH, Brasilia, Brazil, in order to obtain information to establish management measures to control foot rot of sweet potatoes. When symptomless infected cuttings were utilized the stand had a seven‐fold reduction as compared to disease‐free cuttings. Among the five sweet potato cultivars released by EMBRAPA, ‘Brazlandia Branca’ was very susceptible to foot rot, whereas ‘Princesa’ showed the same level of resistance as ‘Morada INTA’, an Argentinian cultivar used as a resistant control. Stem cuttings from the younger extremity of the vine yielded significantly less diseased plants than cuttings taken from lower sections of the vine. Among seven fungicides tested for stem‐cutting disinfection, thiabendazole was the most effective, followed by PCNB, benomyl, iprodione, and captan. Chlorothalonil and mancozeb did not differ from the non‐treated control. These results are discussed in view of other management measures to control foot rot.