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Paul S. Dyer - One of the best experts on this subject based on the ideXlab platform.
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first report of apothecia of Tapesia yallundae occurring on the wild grass holcus lanatus yorkshire fog in new zealand
Plant Pathology, 2002Co-Authors: Paul S. Dyer, Rosie E BradshawAbstract:Tapesia yallundae is a causal agent of eyespot, a damaging stem base disease of cereal crops. The pathogen has also been detected on many wild and cultivated grasses even if characteristic eyespot symptoms are not visible (Lucas et al ., 2000). The pathogen exhibits a heterothallic mating system and apothecia of the sexual stage have been detected on straw stubble in many European countries, Australasia, southern Africa and North America (Dyer et al ., 2001). During field studies in New Zealand in 1995, apothecia resembling those of T. yallundae were discovered on decaying stem bases of Holcus lanatus (Yorkshire Fog) at the margin of one wheat field near Carterton, Wairarapa, North Island. To verify that apothecia were indeed T. yallundae , ascospore discharge was induced and single ascospore cultures established. Resultant colonies were confirmed as T. yallundae on the basis of conidia and colony morphology, and growth rate (2·3 ± 0·1 mm day − 1 ) on potato dextrose agar (Dyer et al ., 1996). Isolates from H. lanatus also produced a 1·05-kb PCR product characteristic of T. yallundae following amplification with the speciesspecific primers Ty 16F and Ty 16R (Nicholson et al ., 1997). No product was obtained with primers specific to the closely related species T. acuformis . Furthermore, amplification with RAPD primer OPA-10 resulted in the production of 0·68and 1·32-kb bands, again characteristic of T. yallundae (Dyer et al ., 1996). Finally, inoculation of wheat seedlings (cv. Avalon) with conidial suspensions resulted in production of characteristic eyespot lesions. This represents the first report of apothecia of T. yallundae occurring on H. lanatus and the first evidence of infection of H. lanatus by T. yallundae . The sexual stage of T. yallundae has also been detected on the wild grasses Bromus diandrus and Hordeum leporinum (barley grass) (Wallwork, 1987). Should the sexual cycle occur regularly on wild grasses then these species may provide an important reservoir of eyespot disease able to infect nearby cereal crops as a result of the dispersal of airborne ascospores. This problem may be exacerbated by the recent establishment of grassy islands (‘beetle banks’) as wildlife refuges in UK crops.
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first report of apothecia of Tapesia yallundae occurring on the wild grass holcus lanatus yorkshire fog in new zealand
Plant Pathology, 2002Co-Authors: Paul S. Dyer, Rosie E BradshawAbstract:Tapesia yallundae is a causal agent of eyespot, a damaging stem base disease of cereal crops. The pathogen has also been detected on many wild and cultivated grasses even if characteristic eyespot symptoms are not visible (Lucas et al ., 2000). The pathogen exhibits a heterothallic mating system and apothecia of the sexual stage have been detected on straw stubble in many European countries, Australasia, southern Africa and North America (Dyer et al ., 2001). During field studies in New Zealand in 1995, apothecia resembling those of T. yallundae were discovered on decaying stem bases of Holcus lanatus (Yorkshire Fog) at the margin of one wheat field near Carterton, Wairarapa, North Island. To verify that apothecia were indeed T. yallundae , ascospore discharge was induced and single ascospore cultures established. Resultant colonies were confirmed as T. yallundae on the basis of conidia and colony morphology, and growth rate (2·3 ± 0·1 mm day − 1 ) on potato dextrose agar (Dyer et al ., 1996). Isolates from H. lanatus also produced a 1·05-kb PCR product characteristic of T. yallundae following amplification with the speciesspecific primers Ty 16F and Ty 16R (Nicholson et al ., 1997). No product was obtained with primers specific to the closely related species T. acuformis . Furthermore, amplification with RAPD primer OPA-10 resulted in the production of 0·68and 1·32-kb bands, again characteristic of T. yallundae (Dyer et al ., 1996). Finally, inoculation of wheat seedlings (cv. Avalon) with conidial suspensions resulted in production of characteristic eyespot lesions. This represents the first report of apothecia of T. yallundae occurring on H. lanatus and the first evidence of infection of H. lanatus by T. yallundae . The sexual stage of T. yallundae has also been detected on the wild grasses Bromus diandrus and Hordeum leporinum (barley grass) (Wallwork, 1987). Should the sexual cycle occur regularly on wild grasses then these species may provide an important reservoir of eyespot disease able to infect nearby cereal crops as a result of the dispersal of airborne ascospores. This problem may be exacerbated by the recent establishment of grassy islands (‘beetle banks’) as wildlife refuges in UK crops.
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species and mating type distribution of Tapesia yallundae and t acuformis and occurrence of apothecia in the u s pacific northwest
Phytopathology, 2002Co-Authors: Greg W Douhan, Timothy D. Murray, Paul S. DyerAbstract:ABSTRACT Eyespot of wheat is caused by the discomycete fungi Tapesia yallundae and T. acuformis. T. yallundae is considered the most important causal agent of the disease in this region but no apothecia of either species have been found in the U.S. Pacific Northwest (PNW). Two compatible isolates of T. yallundae from the PNW were used to inoculate a field plot in the fall of 1998 and apothecia developed in the spring and fall of 2000 on standing wheat stubble. In the spring of 2000, wheat stubble from eight naturally infected fields was examined for the presence of apothecia of T. yallundae and T. acuformis. Apothecia of T. acuformis were found in two fields but no apothecia of T. yallundae were found. This is the first report of apothecia of the eyespot pathogens occurring in the PNW. Species and mating-type distribution of T. yallundae and T. acuformis in the PNW were determined from 817 isolates collected from diseased wheat over 3 years at spatial scales ranging from within fields to across states. In...
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species and mating type distribution of Tapesia yallundae and t acuformis and occurrence of apothecia in the u s pacific northwest
Phytopathology, 2002Co-Authors: Greg W Douhan, T D Murray, Paul S. DyerAbstract:ABSTRACT Eyespot of wheat is caused by the discomycete fungi Tapesia yallundae and T. acuformis. T. yallundae is considered the most important causal agent of the disease in this region but no apothecia of either species have been found in the U.S. Pacific Northwest (PNW). Two compatible isolates of T. yallundae from the PNW were used to inoculate a field plot in the fall of 1998 and apothecia developed in the spring and fall of 2000 on standing wheat stubble. In the spring of 2000, wheat stubble from eight naturally infected fields was examined for the presence of apothecia of T. yallundae and T. acuformis. Apothecia of T. acuformis were found in two fields but no apothecia of T. yallundae were found. This is the first report of apothecia of the eyespot pathogens occurring in the PNW. Species and mating-type distribution of T. yallundae and T. acuformis in the PNW were determined from 817 isolates collected from diseased wheat over 3 years at spatial scales ranging from within fields to across states. In all, 460 isolates were identified as T. yallundae and 357 isolates were identified as T. acuformis with MAT1-1/MAT1-2 ratios not significantly different from 1:1 based on chi(2) tests at most scales tested. The apparent increase in frequency of T. acuformis from previous surveys may indicate a shift in the predominant species causing eyespot. The occurrence of apothecia under field conditions, along with the widespread distribution of mating types of both species, suggests that sexual reproduction may be occurring in both species.
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a multiplex pcr test for determination of mating type applied to the plant pathogens Tapesia yallundae and Tapesia acuformis
Fungal Genetics and Biology, 2001Co-Authors: Paul S. Dyer, Greg W Douhan, P A Furneaux, T D MurrayAbstract:Abstract A multiplex PCR test for determining mating type of the pathogens Tapesia yallundae and Tapesia acuformis is described. The test involves three primers: a “common” primer annealing to DNA sequence conserved in the flanking region of both mating-type idiomorphs and two specific primers annealing to sequence in either the MAT-1 or the MAT-2 idiomorphs. Locating the specific primers in different positions relative to the common primer yielded PCR products of 812 or 418 bp from MAT-1 and MAT-2 isolates, respectively. The test was used successfully to determine the mating type of 118 isolates of T. yallundae and T. acuformis from Europe, North America, and New Zealand. Isolates of both mating types were found on all continents for both species despite the rarely observed occurrence of sexual reproduction of T. acuformis. The multiplex test design should be applicable to other ascomycete species, of use in studies of MAT distribution and facilitating sexual crossing by identifying compatible isolates.
J A Lucas - One of the best experts on this subject based on the ideXlab platform.
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cloning of the cyp51 gene from the eyespot pathogen Tapesia yallundae indicates that resistance to the dmi fungicide prochloraz is not related to sequence changes in the gene encoding the target site enzyme
Fems Microbiology Letters, 2001Co-Authors: Henry M Wood, J A Lucas, Matthew Dickinson, Paul S. DyerAbstract:Resistance to sterol 14α-demethylase inhibitor (DMI) fungicides has been correlated with mutations in the CYP51 gene encoding the target enzyme eburicol 14α-demethylase. CYP51 was isolated from the eyespot pathogen Tapesia yallundae revealing a predicted 526-amino acid product exhibiting homology to other fungal CYP51s. CYP51 was sequenced from four field isolates sensitive or resistant to the DMI fungicide prochloraz and partially sequenced from two further isolates and eight progeny from a cross between prochloraz-sensitive and -resistant parents. Two alleles of the gene were detected termed CYP51-1 and CYP51-2. No correlation was found between sequence change and fungicide sensitivity. Therefore prochloraz resistance involved a mechanism other than mutation in the target site gene.
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genetic control of resistance to the sterol 14α demethylase inhibitor fungicide prochloraz in the cereal eyespot pathogen Tapesia yallundae
Applied and Environmental Microbiology, 2000Co-Authors: Paul S. Dyer, Jacqueline Hansen, Andrew Delaney, J A LucasAbstract:Sexual crosses were used to determine the genetic basis of resistance to the sterol 14 α-demethylase inhibitor fungicide prochloraz in the cereal eyespot pathogen Tapesia yallundae. Three different crosses between sensitive parental strains (22-432 and 22-433 [the concentration required to inhibit growth by 50% {IG50} for each was ≤0.03 mg/liter]) and field isolates from France and New Zealand with differing levels of resistance (PR11 [IG50 = 0.5 mg/liter], PR1 [IG50 = 1.0 mg/liter], and 11-3-18 [IG50 = 2.4 mg/liter]) yielded progeny showing a bimodal distribution, with an even number of sensitive and resistant progeny. This indicated the segregation of a single major gene for resistance in each cross, which was confirmed by the use of backcrosses, crosses between F1 progeny, and control crosses between sensitive parents. However, there was also evidence of additional quantitative genetic components responsible for the increased IG50s of the more resistant isolates. A further cross was made between isolate PR11 and an F1 progeny arising from isolate 11-3-18, and this also yielded progeny which were entirely prochloraz resistant. This suggested that resistance genes were allelic in these two isolates, with resistance conferred by a gene at the same locus (or closely linked loci), despite the fact that the isolates (PR11 and 11-3-18) originated from different continents.
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use of an isocitrate lyase promoter gfp fusion to monitor carbon metabolism of the plant pathogen Tapesia yallundae during infection of wheat
Molecular Plant Pathology, 2000Co-Authors: Paul Bowyer, Elisabeth Mueller, J A LucasAbstract:Abstract Green fluorescent protein (GFP) has been used as a vital marker in a variety of species. Here, we present the use of a GFP-promoter fusion to visualize carbon metabolism in a pathogenic fungus during growth on defined medium and during infection of plants. Isocitrate lyase (ICL), a key enzyme in carbon metabolism, is tightly regulated at the transcriptional level, with high levels of expression during 2-carbon growth and no expression during growth on glucose. A GFP-ICL promoter fusion was used to visualize carbon metabolism in the plant pathogenic fungus Tapesia yallundae during growth in vitro and in the host plant. The ICL promoter from Neurospora crassa retained its native induction and repression characteristics in T. yallundae. Loss of GFP fluorescence from hyphae after repression of the ICL promoter suggested a rapid turnover rate for GFP in T. yallundae. Regulation of this promoter was observed during infection, with expression occurring only on the plant surface, suggesting that 2-carbon metabolism occurs during this phase. These data suggest that GFP is a useful vital marker for the in planta imaging of fungal metabolism.
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Tapesia acuformis as a causal agent of eyespot disease of cereals and evidence for a heterothallic mating system using molecular markers
Fungal Biology, 1996Co-Authors: Paul S. Dyer, J A Lucas, P Nicholson, John F PeberdyAbstract:Isolates of the eyespot pathogen of cereals may be differentiated into two main groups on the basis of a series of cultural and molecular markers. A heterothallic mating system with mating types MAT1-1 and MAT1-2 has already been demonstrated in one group, Tapesia yallundae. A comparable mating system is now described in the other group based on results from in vitro crosses in which the sexual cycle was induced on straw segments incubated at 7 °C or less under nuv or white light for a minimum of 8 months. Recombination between two parental strains was detected using randomly amplified polymorphic DNA (RAPD) molecular markers, and this led to the appearance of novel phenotypes amongst the ascospore progeny including the generation of a new RAPD band not present in either parent. In vitro crossing tests also revealed that the two main groups were sexually incompatible and thus represent genetically isolated biological species. The names T. yallundae and T. acuformis are accepted for the two species. Criteria to accurately distinguish the species are proposed based on mating ability and molecular markers, rather than less reliable tests comparing morphology in culture, and these are successfully used to differentiate a series of 30 test isolates.
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incidence of apothecia of Tapesia yallundae at setaside sites in england and sensitivity of the ascospore offspring to the fungicides benomyl and prochloraz
Plant Pathology, 1995Co-Authors: Paul S. Dyer, J A LucasAbstract:A total of 45 field sites in England were surveyed once for the presence of apothecia of Tapesia yallundae from 1992 to 1994. Apothecia were found at 21 locations and were mainly present on less than 3% of stems. However, apothecia were found on 15-32% of stems at four sites. Analysis of the growth characteristics of ascospore isolates from seven sites showed that most produced colonies characteristic of the W-type of T. yallundae, with only one site yielding the R-type. Most ascospore isolates were resistant to the fungicide benomyl and effectively all remained sensitive to prochloraz. The results of the study are discussed in relation to the fungicidal control and epidemiology of T. yallundae, and the risk of spread of disease from set-aside sites.
Rosie E Bradshaw - One of the best experts on this subject based on the ideXlab platform.
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first report of apothecia of Tapesia yallundae occurring on the wild grass holcus lanatus yorkshire fog in new zealand
Plant Pathology, 2002Co-Authors: Paul S. Dyer, Rosie E BradshawAbstract:Tapesia yallundae is a causal agent of eyespot, a damaging stem base disease of cereal crops. The pathogen has also been detected on many wild and cultivated grasses even if characteristic eyespot symptoms are not visible (Lucas et al ., 2000). The pathogen exhibits a heterothallic mating system and apothecia of the sexual stage have been detected on straw stubble in many European countries, Australasia, southern Africa and North America (Dyer et al ., 2001). During field studies in New Zealand in 1995, apothecia resembling those of T. yallundae were discovered on decaying stem bases of Holcus lanatus (Yorkshire Fog) at the margin of one wheat field near Carterton, Wairarapa, North Island. To verify that apothecia were indeed T. yallundae , ascospore discharge was induced and single ascospore cultures established. Resultant colonies were confirmed as T. yallundae on the basis of conidia and colony morphology, and growth rate (2·3 ± 0·1 mm day − 1 ) on potato dextrose agar (Dyer et al ., 1996). Isolates from H. lanatus also produced a 1·05-kb PCR product characteristic of T. yallundae following amplification with the speciesspecific primers Ty 16F and Ty 16R (Nicholson et al ., 1997). No product was obtained with primers specific to the closely related species T. acuformis . Furthermore, amplification with RAPD primer OPA-10 resulted in the production of 0·68and 1·32-kb bands, again characteristic of T. yallundae (Dyer et al ., 1996). Finally, inoculation of wheat seedlings (cv. Avalon) with conidial suspensions resulted in production of characteristic eyespot lesions. This represents the first report of apothecia of T. yallundae occurring on H. lanatus and the first evidence of infection of H. lanatus by T. yallundae . The sexual stage of T. yallundae has also been detected on the wild grasses Bromus diandrus and Hordeum leporinum (barley grass) (Wallwork, 1987). Should the sexual cycle occur regularly on wild grasses then these species may provide an important reservoir of eyespot disease able to infect nearby cereal crops as a result of the dispersal of airborne ascospores. This problem may be exacerbated by the recent establishment of grassy islands (‘beetle banks’) as wildlife refuges in UK crops.
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first report of apothecia of Tapesia yallundae occurring on the wild grass holcus lanatus yorkshire fog in new zealand
Plant Pathology, 2002Co-Authors: Paul S. Dyer, Rosie E BradshawAbstract:Tapesia yallundae is a causal agent of eyespot, a damaging stem base disease of cereal crops. The pathogen has also been detected on many wild and cultivated grasses even if characteristic eyespot symptoms are not visible (Lucas et al ., 2000). The pathogen exhibits a heterothallic mating system and apothecia of the sexual stage have been detected on straw stubble in many European countries, Australasia, southern Africa and North America (Dyer et al ., 2001). During field studies in New Zealand in 1995, apothecia resembling those of T. yallundae were discovered on decaying stem bases of Holcus lanatus (Yorkshire Fog) at the margin of one wheat field near Carterton, Wairarapa, North Island. To verify that apothecia were indeed T. yallundae , ascospore discharge was induced and single ascospore cultures established. Resultant colonies were confirmed as T. yallundae on the basis of conidia and colony morphology, and growth rate (2·3 ± 0·1 mm day − 1 ) on potato dextrose agar (Dyer et al ., 1996). Isolates from H. lanatus also produced a 1·05-kb PCR product characteristic of T. yallundae following amplification with the speciesspecific primers Ty 16F and Ty 16R (Nicholson et al ., 1997). No product was obtained with primers specific to the closely related species T. acuformis . Furthermore, amplification with RAPD primer OPA-10 resulted in the production of 0·68and 1·32-kb bands, again characteristic of T. yallundae (Dyer et al ., 1996). Finally, inoculation of wheat seedlings (cv. Avalon) with conidial suspensions resulted in production of characteristic eyespot lesions. This represents the first report of apothecia of T. yallundae occurring on H. lanatus and the first evidence of infection of H. lanatus by T. yallundae . The sexual stage of T. yallundae has also been detected on the wild grasses Bromus diandrus and Hordeum leporinum (barley grass) (Wallwork, 1987). Should the sexual cycle occur regularly on wild grasses then these species may provide an important reservoir of eyespot disease able to infect nearby cereal crops as a result of the dispersal of airborne ascospores. This problem may be exacerbated by the recent establishment of grassy islands (‘beetle banks’) as wildlife refuges in UK crops.
John F Peberdy - One of the best experts on this subject based on the ideXlab platform.
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Tapesia acuformis as a causal agent of eyespot disease of cereals and evidence for a heterothallic mating system using molecular markers
Fungal Biology, 1996Co-Authors: Paul S. Dyer, J A Lucas, P Nicholson, John F PeberdyAbstract:Isolates of the eyespot pathogen of cereals may be differentiated into two main groups on the basis of a series of cultural and molecular markers. A heterothallic mating system with mating types MAT1-1 and MAT1-2 has already been demonstrated in one group, Tapesia yallundae. A comparable mating system is now described in the other group based on results from in vitro crosses in which the sexual cycle was induced on straw segments incubated at 7 °C or less under nuv or white light for a minimum of 8 months. Recombination between two parental strains was detected using randomly amplified polymorphic DNA (RAPD) molecular markers, and this led to the appearance of novel phenotypes amongst the ascospore progeny including the generation of a new RAPD band not present in either parent. In vitro crossing tests also revealed that the two main groups were sexually incompatible and thus represent genetically isolated biological species. The names T. yallundae and T. acuformis are accepted for the two species. Criteria to accurately distinguish the species are proposed based on mating ability and molecular markers, rather than less reliable tests comparing morphology in culture, and these are successfully used to differentiate a series of 30 test isolates.
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seasonal development of apothecia of the cereal eyespot pathogen Tapesia yallundae on straw stubble in the uk
Annals of Applied Biology, 1994Co-Authors: Paul S. Dyer, J A Lucas, G L Bateman, John F PeberdyAbstract:Five field sites growing winter wheat were inoculated with isolates of the W- and R-types of Tapesia yallundae in 1990 and 1991. After harvest, plots of uncultivated stubble were monitored for the production of apothecia during 1992 and 1993. Apothecia were found on the stem bases of straw stubble over a 9-month period from mid-October to July, but with a peak in numbers present during late January to March, 5 to 7 months after harvest. This was associated with mean monthly temperatures between 3 degrees C and 8 degrees C. Rainfall appeared to be less important than temperature in apothecial development. Single ascospore isolates obtained from apothecia collected from areas inoculated with W-, R-, or mixed W- and R-type isolates all produced colonies with morphologies and growth rates characteristic of the W-type. Thus there was no indication that the W- and R-types are sexually compatible.
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isolation of r type progeny of Tapesia yallundae from apothecia on wheat stubble in england
Plant Pathology, 1994Co-Authors: Paul S. Dyer, J A Lucas, M Papaikonomou, John F PeberdyAbstract:Apothecia of Tapesia yallundae were collected from a set-aside straw stubble site in Lincolnshire in March 1993. Single ascospore isolates were obtained which produced colonies with morphologies and growth rates characteristic of the R-pathotype of Pseudocercosporella herpotrichoides. Isolates were confirmed to be R-type by the use of randomly amplified polymorphic DNA (RAPD) markers. These observations confirm that T. yallundae is the teleomorph of the R-type of P. herpotrichoides and represent the first detection of the sexual stage of the R-type in the UK.
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Two-allele heterothallism in Tapesia yallundae, the teleomorph of the cereal eyespot pathogen Pseudocercosporella herpotrichoides
Physiological and Molecular Plant Pathology, 1993Co-Authors: Paul S. Dyer, H N Rezanoor, P Nicholson, John A. Lucas, John F PeberdyAbstract:Abstract A technique is described which permits in vitro sexual reproduction between compatible isolates of Tapesia yallundae . It involves the inoculation of isolates onto either barley straw nodal segments or a compost malt medium, followed by incubation for 12 weeks under white light at 10°C. Mating studies were made in which tester strains were crossed against a range of isolates of the W-pathotype of Pseudocercosporella herpotrichoides and pairwise crosses were made between a series of ascospore offspring from the same apothecium. These revealed that T. yallundae exhibits two-allele heterothallism, with the two mating types designated MAT1 -1 and MAT1 -2. Increased phenotypic variation was observed as a result of recombination during the sexual cycle with the appearance of novel phenotypes, differing from those of the parental strains, amongst the progeny of a defined cross. Recombination was detected between mating type, resistance to the fungicide benomyl and randomly amplified polymorphic DNA (RAPD) markers.
Pierre Leroux - One of the best experts on this subject based on the ideXlab platform.
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Polymorphism of 14α-demethylase Gene (CYP51) in the Cereal Eyespot Fungi Tapesia acuformis and Tapesia yallundae
European Journal of Plant Pathology, 2003Co-Authors: Catherine Albertini, Michel Gredt, Pierre LerouxAbstract:Cereal eyespot fungi Tapesia acuformis and Tapesia yallundae are closely related species which show different behaviours upon treatment with sterol 14α-demethylase inhibitors (DMIs). T. acuformis is naturally resistant to DMIs belonging to the triazole family and susceptible to the imidazole ones, whilst T. yallundae is sensitive to both inhibitors. Cloning of the target enzyme gene, CYP51 , from the two species revealed an important polymorphism between them. Further sequencing of CYP51 from sixteen T. acuformis and eleven T. yallundae strains with different phenotypes with regards to resistance to DMIs confirmed that at least eleven variations are species related. Among them, a conserved phenylalanine residue at position 180, found both in T. yallundae and in all known CYP51 proteins from filamentous fungi and yeast, was replaced in T. acuformis by a leucine. Therefore, a leucine at 180 could be possibly involved in natural resistance of T. acuformis to triazoles. Other mutations were observed in some resistant strains, sometimes simultaneously, but in contrast to what was reported for other filamentous fungi, where a mutation at the 136 position of the CYP51 gene product seemed to correlate with resistance to DMIs, we did not find a clear relationship between a given mutation and a particular phenotype. This result suggests that resistance to DMIs could have a polygenic nature in Tapesia . We took advantage of species-related variations to develop a PCR-based assay allowing rapid and easy discrimination between field strains of the two species.
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le pietin verse des cereales caracteristiques et distribution des souches de Tapesia acuformis et Tapesia yallundae resistantes aux fongicides en france
Phytoma. La Défense des Végétaux (France), 2003Co-Authors: Pierre Leroux, Catherine Albertini, Annick Arnold, Michel GredtAbstract:Les isolats fongiques responsables du pietin-verse des cereales peuvent etre separes en deux groupes, consideres aujourd'hui comme deux especes : Tapetia acuformis et Tapesia yallundae. Vis-a-vis des benzimidazoles qui ont ete les premiers fongicides utilises en pratique contre cette maladie, la resistance acquise est liee chez les deux especes aux memes mutations alleliques du gene codant pour la β-tubuline; cette resistance qualitative apparait persistante. Les inhibiteurs de la 14α-demethylation des sterols ou IDM constituent le second groupe de fongicides anti pietin-verse qui renferme des triazoles (ex. bromuconazole, epoxiconazole, flusilazole) et un imidazole, le prochloraze. T. acuformis est naturellement resistant aux triazoles et l'utilisation intensive du prochloraze a entraine la selection de souches resistantes a cet imidazole; cette resistance semble qualitative et persistante. Chez T. yallundae, une resistance quantitative vis-a-vis des triazoles s'est generalisee en France au cours de la derniere decennie. Plus recemment, des souches resistant simultanement aux triazoles et au prochloraze se sont developpees dans de nombreuses regions cerealieres francaises et cette resistance semble etre de type qualitatif. Enfin depuis trois ans, des souches resistantes au cyprodinil ont ete decelees chez les deux especes de Tapesia spp en France, sans toutefois avoir entraine des baisses d'efficacite de cette anilinopyrimidine, qui represente la derniere famille d'anti pietin-verse.
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mutations of the β tubulin gene associated with different phenotypes of benzimidazole resistance in the cereal eyespot fungi Tapesia yallundae and Tapesia acuformis
Pesticide Biochemistry and Physiology, 1999Co-Authors: Catherine Albertini, Michel Gredt, Pierre LerouxAbstract:Abstract Seven phenotypes were identified among field isolates of Tapesia yallundae and Tapesia acuformis when tested for susceptibility to the benzimidazole fungicides carbendazim and thiabendazole and the N-phenylcarbamates diethofencarb, MDPC, and swep. PCR was used to amplify and sequence 627-bp fragments of the β-tubulin gene from 32 Tapesia spp. strains representing the seven field phenotypes and from six T. yallundae laboratory mutants. All benzimidazole-resistant field isolates analyzed had a punctual allelic mutation at codon 198, 200, or 240 of the β-tubulin gene fragment. Codon 198, which encodes glutamic acid in benzimidazole-sensitive strains (resistant to N-phenylcarbamates), was converted to a codon for alanine, glycine, lysine, or glutamine in benzimidazole-resistant strains exhibiting increased sensitivity toward the N-chlorophenylcarbamates MDPC and swep; the first two allelic mutations (alanine and glycine) also conferred susceptibility to diethofencarb. In T. yallundae, benzimidazole-resistant phenotypes, which remained resistant to all the tested N-phenylcarbamates, had a tyrosine instead of a phenylalanine at codon 200 or a phenylalanine instead of a leucine at codon 240. In T. acuformis, however, the change of a phenylalanine at codon 200 for a tyrosine conferred a weaker susceptibility to MDPC and swep as well as a reduced resistance to benzimidazoles compared to their T. yallundae counterparts. The same molecular analysis was performed with T. yallundae laboratory mutants obtained after UV mutagenesis and selection on carbendazim or diethofencarb of a former benzimidazole-sensitive or benzimidazole-resistant field strain. We found in two mutants a punctual change at codon 198, replacing the glutamic acid by a glycine or an aspartic acid, but multiple mutations were observed in the four other mutant strains: a double mutation in codon 198 resulting in the substitution of the glutamic acid by a threonine; a mutation at codon 198 (an alanine instead of a glutamic acid) and a mutation at codon 200 (a serine instead of a phenylalanine); a mutation at codon 198 (an alanine instead of a glutamic acid) and a mutation at codon 250 (a phenylalanine instead of a leucine); and one mutant had four codon changes: at codon 179 (a glycine substituting a valine), at codon 185 (a serine replacing an alanine), at codon 190 (an asparagine replacing a histidine), and at codon 198 (an alanine instead of a glutamic acid). We show here that each different phenotype could be correlated with particular mutations at the β-tubulin gene level.
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evolution of fungicide resistance in the cereal eyespot fungi Tapesia yallundae and Tapesia acuformis in france
Pesticide Science, 1997Co-Authors: Pierre Leroux, Michel GredtAbstract:Field isolates of the cereal eyespot pathogen can be divided into two groups which are now considered as two species: Tapesia yallundae and Tapesia acuformis. In both species the first case of acquired resistance was observed with benzimidazole fungicides in the early 1980s. At the same time, a number of sterol C-14 demethylation inhibitors (DMIs), such as the imidazole prochloraz and several triazoles, including flusilazole, were introduced. Surprisingly T. acuformis appeared intrinsically resistant to the triazole derivatives in comparison to T. yallundae, but both species were sensitive to prochloraz. The intensive use of these DMIs led to the development of acquired resistance towards triazoles in T. yallundae and towards prochloraz in T. acuformis. Today all the strains in both species appear equally sensitive to the anilinopyrimidine cyprodinil.
