Phenylamide Fungicides Metalaxyl Research Articles

The Efficacy of Ethaboxam as a Soybean Seed Treatment Toward Phytophthora, Phytopythium, and Pythium in Ohio.

Phytophthora, Phytopythium, and Pythium species that cause early-season seed decay and pre-emergence and post-emergence damping off of soybean are most commonly managed with seed treatments. The phenylamide fungicides metalaxyl and mefenoxam, and ethaboxam are effective toward some but not all species. The primary objective of this study was to evaluate the efficacy of ethaboxam in fungicide mixtures and compare those with other fungicides as seed treatments to protect soybean against Pythium, Phytopythium, and Phytophthora species in both high-disease field environments and laboratory seed plate assays. The second objective was to evaluate these seed treatment mixtures on cultivars that have varying levels and combinations of resistance to these soilborne pathogens. Five of eight environments received adequate precipitation in the 14 days after planting for high levels of seedling disease development and treatment evaluations. Three environments had significantly greater stands, and three had significantly greater yield when ethaboxam was used in the seed treatment mixture compared with treatments containing metalaxyl or mefenoxam alone. Three fungicide formulations significantly reduced disease severity compared with nontreated in the seed plate assay for 17 species. However, the combination of ethaboxam plus metalaxyl in a mixture was more effective than either fungicide alone against some Pythium and Phytopythium species. Overall, our results indicate that the addition of ethaboxam to a fungicide seed treatment is effective in reducing seed rot caused by these pathogens commonly isolated from soybean in Ohio but that these effects can be masked when cultivars with resistance are planted.

Metabolism and spatial distribution of metalaxyl in tomato plants grown under hydroponic conditions

Knowledge about translocation of plant protection products (PPP's) in plants is important to understand the uptake via the root system. Here we report the combination of analysis of tissue extracts by LC-HRMSn, autoradiography of 14C-labeled compounds and MALDI-MSI, which combine qualitative and quantitative information of chemical composition and the spatial distribution of PPP's and their metabolites in situ. Therefore, the uptake of the phenylamide fungicide metalaxyl was studied in tomato plants (Solanum lycopersicum) using a hydroponic system. The plants have been cultivated in perlite until the two-leaf stage and were transferred into the hydroponic test system afterwards. The radioactive labeled fungicide was readily taken up by the roots during the normal water consumption and radioactivity was translocated uniformly to the aboveground part of the tomato plants, while only small proportion of the applied radioactivity were observed in the roots. The distribution of metalaxyl after the plant uptake experiment in the primary roots where analyzed by a transversal tissue section in the zone of maturation. Metalaxyl is mainly localized in root xylem and in cortex located at the epidermis. With LC-HRMSn and radiochemical analyses of stem and leaf, no parent compound was detectable. Four polar metabolites were the main identified components of the residue and could be visualized by MALDI-imaging mass spectrometry. With these results we could show, that the fungicide metalaxyl is taken up by the plant via the roots during the regular water consumption and transported to xylem.

Experimental and theoretical spectroscopic analysis, chemical reactivity and fungicidal activity study on benalaxyl along with quantum chemical computation on metalaxyl and furalaxyl

Abstract Structural activity, spectroscopic analysis and fungicidal activity plays an important role in understanding the nature of phenylamide fungicides. The objective of the study was to combine experimental spectroscopic and computational methodology together with bioactivity study in order to investigate the structure activity and fungicidal activity of phenyl amide fungicide benalaxyl. Computational study was done on other phenylamide fungicides metalaxyl and furalaxyl using B3LYP/6-311G(d,p) basis set. The complete vibrational distributions were performed on the basis of the potential energy distribution by vibrational energy distribution analysis program. The UV–visible spectrum of benalaxyl in water solvent was taken and analyzed in comparison with TD-DFT method. The potential energy surface scan analysis was performed. The 1H and 13C NMR spectra were recorded and analyzed. Benalaxyl was screened for its antifungal activity. Molecular docking studies were conducted to predict its fungicidal activity. The MIC value of benalaxyl was performed.

Outbreak of a New Phytophthora sp. Associated with Severe Decline of Almond Trees in Eastern Spain

Since 2007, a decline of young almond trees (Prunus dulcis) has been observed in different field-grown nurseries in Valencia (east-central Spain). Early symptoms in affected trees included chlorosis, wilting, cankers, and profuse stem gumming. A Phytophthora sp. was consistently isolated from cankers, roots, and soil of affected trees. It was a heterothallic species with amphigynous and/or paragynous antheridia, and its morphological features did not conform to any of the described Phytophthora species. Pathogenicity was proved by artificial inoculation, completing Koch's postulates. All isolates were sensitive to the phenylamide fungicides metalaxyl and mefenoxam. Amplification and sequencing of the internal transcribed spacer (ITS) region, translation elongation factor 1 alpha gene (EF-1α), the β-tubulin (β-tub) gene, and the region containing the mitochondrial cytochrome c oxidase subunit 1 (cox1) gene fragment identified the species as Phytophthora taxon "niederhauserii", and phylogenetic analyses placed it in Phytophthora Clade 7b.

Tracking the Evolutionary History of the Potato Late Blight Pathogen with Historical Collections

in the mid 19th century in Ireland led to what isknown as the Irish potato famine. Approximately 1.5 millionpeople died from starvation and another 1.5 million weredisplaced and forced to emigrate from Ireland to otherregions of the world. The disease was first observed onpotatoes in the United States in 1843 in areas around theports of Philadelphia and New York (Peterson, Campbell, G Peterson, Campbell, & Griffith, 1992). Thepainstaking work of J. Teschemacher in the United States,M.J. Berkeley in Great Britain, Montagne in France, andlater DeBary in Germany, clearly elucidated that a fungus-like organism was responsible for late blight (Berkeley, 1846,DeBary, 1876; Peterson, Campbell, & Griffith, 1992).Research by early mycologists who studied the late blightpathogen was some of the first to document that fungi werecapable of causing plant disease and laid the groundwork forthe disciplines of microbiology and plant pathology(Berkeley, 1846, DeBary, 1876).Late blight has become an increasingly important diseaseworldwide in recent years, more than 150 years after thegreat famine (Smart and Fry, 2001). Since susceptiblepotatoes are widely planted in many areas of the world, thecrop cannot be grown without frequent fungicideapplication. The disease has reached epidemic proportions inNorth America, Russia, and Europe due to the developmentof resistance to the phenylamide fungicide metalaxyl inpopulations of the pathogen and the widespread occurrenceof new and more virulent genotypes (Drenth et al, 1994;Kadish and Cohen, 1995). Some strains including the Ib orUS-1 clonal lineage are sensitive to the fungicide metalaxyland mefenoxam, while many other strains have developedresistance to these fungicides.More fungicides are used onpotato worldwide, than any other food crop, largely becauseof late blight. The cost of fungicide use by US potato growersexceeds 3 billion dollars annually. The disease can bedevastating in the developing world where fungicides areoften not affordable or available.

Phenotypic and genotypic diversity in Phytophthora infestans on potato in Great Britain, 1995–98

A total of 2691 single‐lesion isolates of Phytophthora infestans was established from samples of late‐blight disease from 354 commercial and garden/allotment sites in Scotland, England and Wales over four growing seasons, 1995–98. The A2 mating type was rare (3·0% of isolates) and was detected at only 34 sites. In vitro tests of sensitivity to the phenylamide fungicide metalaxyl showed that 316 sites yielded isolates with some insensitivity (resistant and/or intermediate); these were more often commercial sites than garden/allotment sites. Over the four seasons, the frequency of isolates with intermediate fungicide sensitivity increased, while the frequency of resistant phenotypes decreased. Resistant isolates were always of A1 mating type. A subset of 1459 isolates from 326 sites was analysed for molecular diversity. Mitochondrial DNA (mtDNA) haplotype Ia predominated (91·0% of isolates); haplotype IIa was present at 54 sites and both haplotypes at 33 sites. The multilocus RFLP probe RG57 detected 30 fingerprints. Four fingerprints were particularly common (RF002, RF006, RF039 and RF040) and 10 were unique to a single site in a single year. The three commonest fingerprints (RF039 > RF002 > RF006) were of A1 mating type and the fourth (RF040) was A2. RF002 isolates were resistant to the phenylamide metalaxyl and were more common in Scotland than in England and Wales. Small sample sizes limited the usefulness of estimates of diversity. Although approximately half of all sites appeared to be colonized by RF039 genotypes, some sites (both commercial and garden/allotment) showed a higher diversity, having both common and unique genotypes. The genotypic diversity within isolates collected from commercial sites and those from garden/allotment sites were similar. The contributions of sexual reproduction and alternatives to sex to the generation of variation are discussed.

Sensitivity to the racemic mixture and isomeric forms of metalaxyl in Indian and European homothallic and heterothallic isolates of Peronospora parasitica in Brassica species

The production of oospores in monoculture (homothallism) and sensitivity to the phenylamide fungicide metalaxyl, in its racemic mixture form of (R)- and (S)-enantiomers (Ridomil-25WP) or the latest isomeric form (R)-enantiomer (Metalaxyl-M), was tested using 11 single-spore and 14 field isolates of Peronospora parasitica. Three isolates were from Brassica napus (UK), 13 from B. juncea (India), four from B. rapa (India), one from Eruca sativa (India) and four from B. oleracea (one from the UK, two from France and one from India). All isolates were found to be homothallic, as they produced oospores in monoculture, except P006 (a UK single-spore isolate derived from B. oleracea and previously known to be insensitive to Ridomil-25WP) which was heterothallic. All isolates were found to be sensitive to the two forms of the phenylamide fungicide metalaxyl (Ridomil-25WP and Metalaxyl-M) except P006 and FP13, a French isolate derived from B. oleracea in Brittany. These isolates were insensitive to both fungicides at the three concentrations used in this study (0.5, 5.0 and 50.0 μg/ml). To our knowledge, this is the first reported case of insensitivity to metalaxyl in P. parasitica from France. This study emphasises the importance of deploying sources of host resistance with fungicides in prolonging the effectiveness of both control procedures.

Aggressiveness and other factors relating to displacement of populations of Phytophthora infestans in England and Wales

Mating type, in vitro sensitivity to the phenylamide fungicide metalaxyl, and mitochondrial (mtDNA) haplotype were determined in some or all of 618 isolates of Phytophthora infestans from the years between 1978 and 1995. A2 mating type occurred infrequently in most but not all years and insensitivity to metalaxyl increased over time. After 1982, the mtDNA Ib haplotype was largely replaced (except for one isolate in 1986 and one in 1995) by two new haplotypes, Ia and IIa. Type Ia was much more common than type IIa. Approximately one quarter of these isolates (165) were compared using two components of fitness associated with aggressiveness (infection frequency × number of sporangia per lesion) on detached leaves of cultivars Maris Piper, Cara and Stirling, which were chosen as exhibiting increasing levels of race non-specific resistance. Isolates were compared with three ‘standard’ isolates of low, intermediate or high aggressiveness, and the data standardised for comparison between experiments. On cvs. Cara and Stirling, but not on Maris Piper, mtDNA Ia and IIa haplotypes were more aggressive than type Ib in several separate experiments. Similarly, metalaxyl sensitive phenotypes were more aggressive than insensitive phenotypes on Cara and Stirling but not on Maris Piper. The displacement of mtDNA type Ib by types Ia and IIa over this period may have been a result of the lower aggressiveness and lack of complete insensitivity to metalaxyl in type Ib isolates.

Widespread Distribution and Probable Origin of Resistance to Metalaxyl in Clonal Genotypes ofPhytophthora infestansin the United States and Western Canada

The sensitivity of 251 isolates of Phytophthora infestans to the phenylamide fungicide metalaxyl was assessed by an in vitro radial growth assay on fungicide-amended agar media. Isolates were collected from many regions of North America from 1987 through 1993, including 15 states in the United States and British Columbia, Canada. A small sample of isolates from Europe and Israel was included for comparison. Isolates that grew less than 40% of the control on media containing 5 μg of metalaxyl per ml were considered sensitive; all other isolates were scored as resistant. Field trials and floating leaf-disk assays were used to confirm the accuracy of the amended-agar technique. All isolates collected from 1987 through 1989 were sensitive. Metalaxyl-resistant isolates were detected in 13 of 15 states and in British Columbia during 1992 and 1993. With one exception, sensitivity to metalaxyl was absolutely correlated with clonal lineage as determined by mating type, allozyme genotype, and DNA fingerprint analysis. The US-I clonal lineage, present in the United States and Canada for many years, was uniformly sensitive. In contrast, all isolates with the recently immigrated US-7 and US-8 clonal genotypes were resistant, even those obtained from fields with no history of metalaxyl application. All US-6 isolates collected since 1990 were resistant, but one sensitive US-6 isolate was collected in California in 1989. The cause of this polymorphism within US-6 could not be determined. Metalaxyl resistance was unimodally distributed within clonal lineages and limited to those that were recently immigrated. This strongly supports the hypothesis that resistance in the United States and Canada originated by migration, rather than by mutation and selection after migration. In contrast, evidence for selection of metalaxyl-resistant mutants within clonal lineages was detected among the limited sample of isolates from Europe and Israel.

Antifungal modes of action of metalaxyl, cyprofuram, benalaxyl and oxadixyl in phenylamide-sensitive and phenylamide-resistant strains of Phytophthora megasperma f. sp. medicaginis and Phytophthora infestans

The activity of the phenylamide fungicides metalaxyl, cyprofuram, benalaxyl and oxadixyl against phenylamide-sensitive and phenylamide-resistant strains of Phytophthora megasperma f. sp. medicaginis and Phytophthora infestans has been compared in several tests. Metalaxyl showed the highest activity amongst the four fungicides against mycelial growth of sensitive strains on agar media. Benalaxyl and cyprofuram showed the highest activity against resistant strains. RNA synthesis of sensitive strains, measured as [ 3H]uridine incorporation, was inhibited by about 80% ( P. megasperma) and by about 40% ( P. infestans) by all phenylamides at concentrations of 1 μg/ml. At higher concentrations inhibition remained at this level, indicating that only part of the RNA synthesis was inhibited. RNA synthesis of resistant strains was completely insensitive to metalaxyl and oxadixyl at concentrations as high as 200 μg/ml. Cyprofuram, however, at concentrations above 1 μg/ml ( P. megasperma) and 10 μg/ml ( P. infestans) was inhibitory and at 200 μg/ml this compound almost completely inhibited the phenylamide-sensitive part of the RNA synthesis of both strains. In contrast to the other phenylamides, benalaxyl affected [ 3H]uridine uptake into mycelium at concentrations higher than 10 μg/ml, and at 100 μg/ml inhibition of uptake was almost total with both sensitive and resistant strains of both Phytophthora species. Inhibition of [ 3H]uridine uptake obviously is a feature of a second mechanism of action of benalaxyl. Endogenous RNA polymerase activity of isolated nuclei from sensitive strains of P. megasperma was inhibited at phenylamide concentrations as low as 0·1 μg/ml whereas that from resistant strains was not affected at concentrations as high as 100 μg/ml. Similarly, endogenous nuclear RNA polymerase activity of sensitive P. infestans strains appeared to be more sensitive to the phenylamides than that of resistant P. infestans strains. This suggests that resistance that developed in field strains of P. infestans has a basis similar to that of mutagen-induced resistance in laboratory strains of P. megasperma. Tests of the fungicidal activity of the phenylamides determined in a lucerne seedling assay ( P. megasperma) and a detached potato leaf assay ( P. infestans) clearly differentiated between sensitive and resistant strains. Resistance levels to cyprofuram and benalaxyl were as high as those to metalaxyl and oxadixyl, indicating that the additional effect of a second mechanism of action of benalaxyl and the property of cyprofuram to inhibit RNA synthesis of resistant strains at higher concentrations are of limited practical importance for counteracting phenylamide resistance.