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Jørgensen LN, van den Bosch F, Oliver RP, Heick TM, Paveley ND. Targeting Fungicide Inputs According to Need. ANNUAL REVIEW OF PHYTOPATHOLOGY 2017; 55:181-203. [PMID: 28525306 DOI: 10.1146/annurev-phyto-080516-035357] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Fungicides should be used to the extent required to minimize economic costs of disease in a given field in a given season. The maximum number of treatments and maximum dose per treatment are set by fungicide manufacturers and regulators at a level that provides effective control under high disease pressure. Lower doses are economically optimal under low or moderate disease pressure, or where other control measures such as resistant cultivars constrain epidemics. Farmers in many countries often apply reduced doses, although they may still apply higher doses than the optimum to insure against losses in high disease seasons. Evidence supports reducing the number of treatments and reducing the applied dose to slow the evolution of fungicide resistance. The continuing research challenge is to improve prediction of future disease damage and account for the combined effect of integrated control measures to estimate the optimum number of treatments and the optimum dose needed to minimize economic costs. The theory for optimizing dose is well developed but requires translation into decision tools because the current basis for farmers' dose decisions is unclear.
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Affiliation(s)
- Lise N Jørgensen
- Department of Agroecology, Aarhus University, DK-4200, Slagelse, Denmark;
| | | | - R P Oliver
- Centre for Crop and Disease Management (CCDM), Curtin University, Bentley, Western Australia, WA-6102, Australia
| | - T M Heick
- Department of Agroecology, Aarhus University, DK-4200, Slagelse, Denmark;
| | - N D Paveley
- ADAS High Mowthorpe, Malton, North Yorkshire, YO17 8BP, United Kingdom
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52
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Hagerty CH, Graebner RC, Sackett KE, Mundt CC. Variable competitive effects of fungicide resistance in field experiments with a plant pathogenic fungus. ECOLOGICAL APPLICATIONS : A PUBLICATION OF THE ECOLOGICAL SOCIETY OF AMERICA 2017; 27:1305-1316. [PMID: 28266146 DOI: 10.1002/eap.1524] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/19/2016] [Revised: 01/26/2017] [Accepted: 02/06/2017] [Indexed: 06/06/2023]
Abstract
Classic evolutionary theory suggests that mutations associated with antimicrobial and pesticide resistance result in a fitness cost in the absence of the selective antimicrobial agent or pesticide. There is experimental evidence to support fitness costs associated with resistance to anti-microbial compounds and pesticides across many biological disciplines, including human pathology, entomology, plant sciences, and plant pathology. However, researchers have also found examples of neutral and increased fitness associated with resistance, where the effect of a given resistance mutation depends on environmental and biological factors. We used Zymoseptoria tritici, a model evolutionary plant pathogenic fungus, to compare the competitive ability of fungicide-resistant isolates to fungicide-sensitive isolates. We conducted four large-scale inoculated winter wheat experiments at Oregon State University agriculture experiment stations. We found a significant change in the frequency of fungicide resistance over time in all four experiments. The direction and magnitude of these changes, however, differed by experimental location, year of experiment, and inoculum resistance treatment (fungicide-resistant, resistant/sensitive mixture, and fungicide-sensitive). These results suggest that the competitive ability of resistant isolates relative to sensitive isolates varied depending upon environmental conditions, including the initial frequency of resistant individuals in the population.
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Affiliation(s)
- Christina H Hagerty
- Columbia Basin Agricultural Research Center, Oregon State University, 48037 Tubbs Ranch Road, Adams, OR, 97801, USA
| | - Ryan C Graebner
- Hermiston Agricultural Research and Extension Center, Oregon State University, 2121 S 1st St, Hermiston, OR, 97838, USA
| | - Kathryn E Sackett
- Department of Botany and Plant Pathology, Oregon State University, Cordley Hall, 2701 SW Campus Way, Corvallis, OR, 97331, USA
| | - Christopher C Mundt
- Department of Botany and Plant Pathology, Oregon State University, Cordley Hall, 2701 SW Campus Way, Corvallis, OR, 97331, USA
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Elisabeth Lof M, de Vallavieille-Pope C, van der Werf W. Achieving Durable Resistance Against Plant Diseases: Scenario Analyses with a National-Scale Spatially Explicit Model for a Wind-Dispersed Plant Pathogen. PHYTOPATHOLOGY 2017; 107:580-589. [PMID: 28095206 DOI: 10.1094/phyto-05-16-0207-r] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Genetic resistance in crops is a cornerstone of disease management in agriculture. Such genetic resistance is often rapidly broken due to selection for virulence in the pathogen population. Here, we ask whether there are strategies that can prolong the useful life of plant resistance genes. In a modeling study, we compared four deployment strategies: gene pyramiding, sequential use, simultaneous use, and a mixed strategy. We developed a spatially explicit model for France and parameterized it for the fungal pathogen Puccinia striiformis f. sp. tritici (causing wheat yellow rust) to test management strategies in a realistic spatial setting. We found that pyramiding two new resistance genes in one variety was the most durable solution only when the virulent genotype had to emerge by mutation. Deploying single-gene-resistant varieties concurrently with the pyramided variety eroded the durability of the gene pyramid. We found that continuation of deployment of varieties with broken-down resistance prolonged the useful life of simultaneous deployment of four single-gene-resistant varieties versus sequential use. However, when virulence was already present in the pathogen population, durability was low and none of the deployment strategies had effect. These results provide guidance on effective strategies for using resistance genes in crop protection practice.
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Affiliation(s)
- Marjolein Elisabeth Lof
- First and third authors: Wageningen University, Centre for Crop Systems Analysis, P.O. Box 430, 6700 AK Wageningen, The Netherlands; and second author: INRA UMR 1290 BIOGER, BP01, 78850 Thiverval-Grignon, France
| | - Claude de Vallavieille-Pope
- First and third authors: Wageningen University, Centre for Crop Systems Analysis, P.O. Box 430, 6700 AK Wageningen, The Netherlands; and second author: INRA UMR 1290 BIOGER, BP01, 78850 Thiverval-Grignon, France
| | - Wopke van der Werf
- First and third authors: Wageningen University, Centre for Crop Systems Analysis, P.O. Box 430, 6700 AK Wageningen, The Netherlands; and second author: INRA UMR 1290 BIOGER, BP01, 78850 Thiverval-Grignon, France
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54
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Mikaberidze A, Paveley N, Bonhoeffer S, van den Bosch F. Emergence of Resistance to Fungicides: The Role of Fungicide Dose. PHYTOPATHOLOGY 2017; 107:545-560. [PMID: 28079455 DOI: 10.1094/phyto-08-16-0297-r] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Resistance to antimicrobial drugs allows pathogens to survive drug treatment. The time taken for a new resistant mutant to reach a population size that is unlikely to die out by chance is called "emergence time." Prolonging emergence time would delay loss of control. We investigate the effect of fungicide dose on the emergence time in fungal plant pathogens. A population dynamical model is combined with dose-response data for Zymoseptoria tritici, an important wheat pathogen. Fungicides suppress sensitive pathogen population. This has two effects. First, the rate of appearance of resistant mutants is reduced, hence the emergence takes longer. Second, more healthy host tissue becomes available for resistant mutants, increasing their chances to invade and accelerates emergence. In theory, the two competing effects may lead to a non-monotonic dependence of the emergence time on fungicide dose that exhibits a minimum. But according to field data, fungicides are unable to reduce the fungicide-sensitive population strongly enough even at high doses. Hence, for full resistance over realistic ranges of pathogen's life history and fungicide dose-response parameters, emergence time decreases monotonically with increasing dose. For partial resistance, there can be cases within a limited parameter range, when emergence decelerates at higher doses.
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Affiliation(s)
- Alexey Mikaberidze
- First author: Plant Pathology Group, Institute of Integrative Biology, ETH Zurich, LFW, Zurich, CH-8092, Switzerland; second author: ADAS, Duggleby YO17 8BP, United Kingdom; third author: Theoretical Biology, Institute of Integrative Biology, ETH Zurich, CHN, Zurich, CH-8092; and fourth author: Rothamsted Research, Harpenden, AL5 2JQ, United Kingdom
| | - Neil Paveley
- First author: Plant Pathology Group, Institute of Integrative Biology, ETH Zurich, LFW, Zurich, CH-8092, Switzerland; second author: ADAS, Duggleby YO17 8BP, United Kingdom; third author: Theoretical Biology, Institute of Integrative Biology, ETH Zurich, CHN, Zurich, CH-8092; and fourth author: Rothamsted Research, Harpenden, AL5 2JQ, United Kingdom
| | - Sebastian Bonhoeffer
- First author: Plant Pathology Group, Institute of Integrative Biology, ETH Zurich, LFW, Zurich, CH-8092, Switzerland; second author: ADAS, Duggleby YO17 8BP, United Kingdom; third author: Theoretical Biology, Institute of Integrative Biology, ETH Zurich, CHN, Zurich, CH-8092; and fourth author: Rothamsted Research, Harpenden, AL5 2JQ, United Kingdom
| | - Frank van den Bosch
- First author: Plant Pathology Group, Institute of Integrative Biology, ETH Zurich, LFW, Zurich, CH-8092, Switzerland; second author: ADAS, Duggleby YO17 8BP, United Kingdom; third author: Theoretical Biology, Institute of Integrative Biology, ETH Zurich, CHN, Zurich, CH-8092; and fourth author: Rothamsted Research, Harpenden, AL5 2JQ, United Kingdom
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55
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Rey T, Dumas B. Plenty Is No Plague: Streptomyces Symbiosis with Crops. TRENDS IN PLANT SCIENCE 2017; 22:30-37. [PMID: 27916552 DOI: 10.1016/j.tplants.2016.10.008] [Citation(s) in RCA: 66] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/07/2016] [Revised: 09/28/2016] [Accepted: 10/13/2016] [Indexed: 05/19/2023]
Abstract
Streptomyces spp. constitute a major clade of the phylum Actinobacteria. These Gram-positive, filamentous prokaryotes are ubiquitous in soils and marine sediments, and are commonly found in the rhizosphere or inside plant roots. Plant-interacting Streptomyces have received limited attention, in contrast to Streptomyces spp. extensively investigated for decades in medicine given their rich potential for secondary metabolite biosynthesis. Recent genomic, metabolomic, and biotechnological advances have produced key insights into Streptomyces spp., paving the way to the use of their metabolites in agriculture. In this Opinion article we propose how Streptomyces spp. could dominate future aspects of crop nutrition and protection. Risks and benefits of the use of these microorganisms in agriculture are also discussed.
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Affiliation(s)
- Thomas Rey
- De Sangosse, Bonnel, 47480 Pont-Du-Casse, France; Laboratoire de Recherche en Sciences Végétales, Université de Toulouse, CNRS, UPS, 24 Chemin de Borde Rouge, Auzeville, BP42617, 31326 Castanet Tolosan, France.
| | - Bernard Dumas
- Laboratoire de Recherche en Sciences Végétales, Université de Toulouse, CNRS, UPS, 24 Chemin de Borde Rouge, Auzeville, BP42617, 31326 Castanet Tolosan, France
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Dooley H, Shaw MW, Mehenni-Ciz J, Spink J, Kildea S. Detection of Zymoseptoria tritici SDHI-insensitive field isolates carrying the SdhC-H152R and SdhD-R47W substitutions. PEST MANAGEMENT SCIENCE 2016; 72:2203-2207. [PMID: 26941011 DOI: 10.1002/ps.4269] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2015] [Revised: 03/01/2016] [Accepted: 03/01/2016] [Indexed: 06/05/2023]
Abstract
BACKGROUND Succinate dehydrogenase inhibitor (SDHI) fungicides are important in the management of Zymoseptoria tritici in wheat. New active ingredients from this group of fungicides have been introduced recently and are widely used. Because the fungicides act at a single enzyme site, resistance development in Z. tritici is classified as medium-to-high risk. RESULTS Isolates from Irish experimental plots in 2015 were tested against the SDHI penthiopyrad during routine monitoring. The median of the population was approximately 2 times less sensitive than the median of the baseline population. Two of the 93 isolates were much less sensitive to penthiopyrad than the least sensitive of the baseline isolates. These isolates were also insensitive to most commercially available SDHIs. Analysis of the succinate dehydrogenase coding genes confirmed the presence of the substitutions SdhC-H152R and SdhD-R47W in the very insensitive isolates. CONCLUSION This is the first report showing that the SdhC-H152R mutation detected in laboratory mutagenesis studies also exists in the field. The function and relevance of this mutation, combined with SdhD-R47W, still needs to be determined. © 2016 Society of Chemical Industry.
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Affiliation(s)
- Hilda Dooley
- Department of Crop Science, TEAGASC Crops, Environment and Land Use Programme, Carlow, Republic of Ireland
- School of Agriculture, Policy and Development, University of Reading, Reading, UK
| | - Michael W Shaw
- School of Agriculture, Policy and Development, University of Reading, Reading, UK
| | - Jeanne Mehenni-Ciz
- Department of Crop Science, TEAGASC Crops, Environment and Land Use Programme, Carlow, Republic of Ireland
| | - John Spink
- Department of Crop Science, TEAGASC Crops, Environment and Land Use Programme, Carlow, Republic of Ireland
| | - Steven Kildea
- Department of Crop Science, TEAGASC Crops, Environment and Land Use Programme, Carlow, Republic of Ireland.
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57
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van den Berg F, Paveley ND, van den Bosch F. Dose and number of applications that maximize fungicide effective life exemplified by Zymoseptoria tritici on wheat - a model analysis. PLANT PATHOLOGY 2016; 65:1380-1389. [PMID: 27708459 PMCID: PMC5027893 DOI: 10.1111/ppa.12558] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Two key decisions that need to be taken about a fungicide treatment programme are (i) the number of applications that should be used per crop growing season, and (ii) the dosage that should be used in each application. There are two opposing considerations, with control efficacy improved by a higher number of applications and higher dose, and resistance management improved by a lower number of applications and lower dose. Resistance management aims to prolong the effective life of the fungicide, defined as the time between its introduction onto the market for use on the target pathogen, and the moment when effective control is lost due to a build-up of fungicide resistance. Thus, the question is whether there are optimal combinations of dose rate and number of applications that both provide effective control and lead to a longer effective life. In this paper, it is shown how a range of spray programmes can be compared and optimal programmes selected. This is explored with Zymoseptoria tritici on wheat and a quinone outside inhibitor (QoI) fungicide. For this pathogen-fungicide combination, a single treatment provided effective control under the simulated disease pressure, but only if the application timing was optimal and the dose was close to the maximum permitted. Programmes with three applications were generally not optimal as they exerted too much selection for resistance. Two-application fungicide programmes balanced effective control with reasonable flexibility of dose and application timing, and low resistance selection, leading to long effective lives of the fungicide.
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Affiliation(s)
- F van den Berg
- Department of Computational and Systems Biology Rothamsted Research Harpenden AL5 2JQ UK
| | - N D Paveley
- ADAS High Mowthorpe Duggleby Malton YO17 8BP UK
| | - F van den Bosch
- Department of Computational and Systems Biology Rothamsted Research Harpenden AL5 2JQ UK
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58
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Kitchen JL, van den Bosch F, Paveley ND, Helps J, van den Berg F. The Evolution of Fungicide Resistance Resulting from Combinations of Foliar-Acting Systemic Seed Treatments and Foliar-Applied Fungicides: A Modeling Analysis. PLoS One 2016; 11:e0161887. [PMID: 27571208 PMCID: PMC5003396 DOI: 10.1371/journal.pone.0161887] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2016] [Accepted: 08/12/2016] [Indexed: 11/18/2022] Open
Abstract
For the treatment of foliar diseases of cereals, fungicides may be applied as foliar sprays or systemic seed treatments which are translocated to leaves. Little research has been done to assess the resistance risks associated with foliar-acting systemic seed treatments when used alone or in combination with foliar sprays, even though both types of treatment may share the same mode of action. It is therefore unknown to what extent adding a systemic seed treatment to a foliar spray programme poses an additional resistance risk and whether in the presence of a seed treatment additional resistance management strategies (such as limiting the total number of treatments) are necessary to limit the evolution of fungicide-resistance. A mathematical model was developed to simulate an epidemic and the resistance evolution of Zymoseptoria tritici on winter wheat, which was used to compare different combinations of seed and foliar treatments by calculating the fungicide effective life, i.e. the number of years before effective disease control is lost to resistance. A range of parameterizations for the seed treatment fungicide and different fungicide uptake models were compared. Despite the different parameterizations, the model consistently predicted the same trends in that i) similar levels of efficacy delivered either by a foliar-acting seed treatment, or a foliar application, resulted in broadly similar resistance selection, ii) adding a foliar-acting seed treatment to a foliar spray programme increased resistance selection and usually decreased effective life, and iii) splitting a given total dose—by adding a seed treatment to foliar treatments, but decreasing dose per treatment—gave effective lives that were the same as, or shorter than those given by the spray programme alone. For our chosen plant-pathogen-fungicide system, the model results suggest that to effectively manage selection for fungicide-resistance, foliar acting systemic seed treatments should be included as one of the maximum number of permitted fungicide applications.
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Affiliation(s)
- James L. Kitchen
- Computational and Systems Biology, Rothamsted Research, Harpenden, Hertfordshire, United Kingdom
| | - Frank van den Bosch
- Computational and Systems Biology, Rothamsted Research, Harpenden, Hertfordshire, United Kingdom
| | - Neil D. Paveley
- Plant Pathology Department, ADAS, High Mowthorpe, Duggleby, North Yorkshire, United Kingdom
| | - Joseph Helps
- Computational and Systems Biology, Rothamsted Research, Harpenden, Hertfordshire, United Kingdom
| | - Femke van den Berg
- Computational and Systems Biology, Rothamsted Research, Harpenden, Hertfordshire, United Kingdom
- * E-mail:
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59
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Newbery F, Qi A, Fitt BD. Modelling impacts of climate change on arable crop diseases: progress, challenges and applications. CURRENT OPINION IN PLANT BIOLOGY 2016; 32:101-109. [PMID: 27471781 DOI: 10.1016/j.pbi.2016.07.002] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/05/2016] [Revised: 06/27/2016] [Accepted: 07/05/2016] [Indexed: 05/20/2023]
Abstract
Combining climate change, crop growth and crop disease models to predict impacts of climate change on crop diseases can guide planning of climate change adaptation strategies to ensure future food security. This review summarises recent developments in modelling climate change impacts on crop diseases, emphasises some major challenges and highlights recent trends. The use of multi-model ensembles in climate change modelling and crop modelling is contributing towards measures of uncertainty in climate change impact projections but other aspects of uncertainty remain largely unexplored. Impact assessments are still concentrated on few crops and few diseases but are beginning to investigate arable crop disease dynamics at the landscape level.
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Affiliation(s)
- Fay Newbery
- School of Agriculture, Policy and Development, University of Reading, Whiteknights, PO Box 237, Reading RG6 6AR, UK
| | - Aiming Qi
- Rothamsted Research, Harpenden, Herts AL5 2JQ, UK; School of Life & Medical Sciences, University of Hertfordshire, Hatfield AL10 9AB, UK
| | - Bruce Dl Fitt
- School of Life & Medical Sciences, University of Hertfordshire, Hatfield AL10 9AB, UK.
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60
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Hagerty CH, Mundt CC. Reduced Virulence of Azoxystrobin-Resistant Zymoseptoria tritici Populations in Greenhouse Assays. PHYTOPATHOLOGY 2016; 106:884-889. [PMID: 27249373 DOI: 10.1094/phyto-01-16-0029-r] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The development of resistance to multiple fungicide classes is currently limiting disease management options for many pathogens, while the discovery of new fungicide classes may become less frequent. In light of this, more research is needed to quantify virulence trade-offs of fungicide resistance in order to more fully understand the implications of fungicide resistance on pathogen fitness. The purpose of this study was to measure the virulence of azoxystrobin-resistant and -sensitive Zymoseptoria tritici populations collected from North and South Willamette Valley, Oregon, in 2012 and 2015. Inoculum mixtures of known fungicide-resistant phenotypes were used to simulate natural field conditions, where multiple genotypes exist and interact in close proximity. Six greenhouse inoculations were conducted over 2 years, and virulence of the isolate mixtures was evaluated in planta. We considered virulence to be "the degree of pathology caused by the organism" and visually estimated the percent area of leaf necrosis as a measure of virulence. In greenhouse conditions, a consistent association of reduced virulence with azoxystrobin-resistant Z. tritici isolate mixtures was observed. North Willamette Valley and South Willamette Valley populations did not differ in virulence.
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Affiliation(s)
- Christina H Hagerty
- Department of Botany and Plant Pathology, Oregon State University, 2082 Cordley Hall, 2701 SW Campus Way, Corvallis 97331
| | - Christopher C Mundt
- Department of Botany and Plant Pathology, Oregon State University, 2082 Cordley Hall, 2701 SW Campus Way, Corvallis 97331
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Dooley H, Shaw MW, Spink J, Kildea S. The effect of succinate dehydrogenase inhibitor/azole mixtures on selection of Zymoseptoria tritici isolates with reduced sensitivity. PEST MANAGEMENT SCIENCE 2016; 72:1150-1159. [PMID: 26269125 DOI: 10.1002/ps.4093] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/19/2015] [Revised: 08/07/2015] [Accepted: 08/10/2015] [Indexed: 06/04/2023]
Abstract
BACKGROUND Combining fungicides with different modes of action is regarded as one of the most effective means of slowing the selection of resistance. Field trials were used to study the effects of such mixtures on selection for Zymoseptoria tritici with reduced sensitivity to the succinate dehydrogenase inhibitors (SDHIs) and azole fungicides. The SDHI isopyrazam and the azole epoxiconazole were applied individually as solo products, and together in a preformulated mixture. All fungicide treatments were included at both full and half the recommended doses. RESULTS Compared with using epoxiconazole alone, mixing epoxiconazole with isopyrazam led to an increase in epoxiconazole-sensitive isolates. In contrast, all treatments containing isopyrazam reduced the sensitivity of Z. tritici to isopyrazam compared with those without. Reducing doses to half the recommended rate had no effect on sensitivity of isolates to either active ingredient. In a subgroup of isolates least sensitive to isopyrazam, non-synonymous mutations were found in the SdhC and SdhD subunits, but their presence was unrelated to sensitivity. CONCLUSION Mixing an azole and SDHI was clearly beneficial for the azole, but not for the SDHI component. This dynamic might change if strains conferring reduced sensitivity to the SDHIs were to arise. © 2015 Society of Chemical Industry.
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Affiliation(s)
- Hilda Dooley
- Department of Crop Science, TEAGASC Crops, Environment and Land Use Programme, Carlow, Republic of Ireland
- School of Agriculture, Policy and Development, University of Reading, Reading, Berks, UK
| | - Michael W Shaw
- School of Agriculture, Policy and Development, University of Reading, Reading, Berks, UK
| | - John Spink
- Department of Crop Science, TEAGASC Crops, Environment and Land Use Programme, Carlow, Republic of Ireland
| | - Steven Kildea
- Department of Crop Science, TEAGASC Crops, Environment and Land Use Programme, Carlow, Republic of Ireland
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62
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Hayes LE, Sackett KE, Anderson NP, Flowers MD, Mundt CC. Evidence of Selection for Fungicide Resistance in Zymoseptoria tritici Populations on Wheat in Western Oregon. PLANT DISEASE 2016; 100:483-489. [PMID: 30694133 DOI: 10.1094/pdis-02-15-0214-re] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
Plant pathogens pose a major challenge to maintaining food security in many parts of the world. Where major plant pathogens are fungal, fungicide resistance can often thwart regional control efforts. Zymoseptoria tritici, causal agent of Septoria tritici blotch, is a major fungal pathogen of wheat that has evolved resistance to chemical control products in four fungicide classes in Europe. Compared with Europe, however, fungicide use has been less and studies of fungicide resistance have been infrequent in North American Z. tritici populations. Here, we confirm first reports of Z. tritici fungicide resistance evolution in western Oregon through analysis of the effects of spray applications of propiconazole and an azoxystrobin + propiconazole mixture during a single growing season. Frequencies of strobilurin-resistant isolates, quantified as proportions of G143A mutants, were significantly higher in azoxystrobin-sprayed plots compared with plots with no azoxystrobin treatment at two different locations and were significantly higher in plots of a moderately resistant cultivar than in plots of a susceptible cultivar. Thus, it appears that western Oregon Z. tritici populations have the potential to evolve levels of strobilurin resistance similar to those observed in Europe. Although the concentration of propiconazole required to reduce pathogen growth by 50% values were numerically greater for isolates collected from plots receiving propiconazole than in control plots, this effect was not significant (P > 0.05).
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Affiliation(s)
| | | | | | | | - Christopher C Mundt
- Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331
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63
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Hughes G, Burnett FJ. Integrating Experience, Evidence and Expertise in the Crop Protection Decision Process. PLANT DISEASE 2015; 99:1197-1203. [PMID: 30695925 DOI: 10.1094/pdis-02-15-0197-fe] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Generically, farm-scale crop protection decision making may be characterized as a process beginning with an initial assessment of disease risk followed by the accumulation of evidence related to current risk factors, leading to a risk prediction. What action is then taken depends on the response of the decision owner, taking into account previous experience, advice from trusted sources, alongside policy or legislative constraints on crop protection practice that are intended to mitigate any impacts that may transcend the farm scale. This process has commonalities with decision-making in the strategy of preventive medicine. This article delves into the clinical literature in order to provide a perspective on some recent discussions of shared decision making presented there, discussions that relate to issues also faced in sustainable crop protection.
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Affiliation(s)
- Gareth Hughes
- Crop and Soil Systems Research Group, SRUC, Edinburgh EH9 3JG, UK
| | - Fiona J Burnett
- Crop and Soil Systems Research Group, SRUC, Edinburgh EH9 3JG, UK
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Frenkel O, Cadle-Davidson L, Wilcox WF, Milgroom MG. Mechanisms of Resistance to an Azole Fungicide in the Grapevine Powdery Mildew Fungus, Erysiphe necator. PHYTOPATHOLOGY 2015; 105:370-7. [PMID: 25271353 DOI: 10.1094/phyto-07-14-0202-r] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
We studied the mechanisms of azole resistance in Erysiphe necator by quantifying the sensitivity to myclobutanil (EC50) in 65 isolates from the eastern United States and 12 from Chile. From each isolate, we sequenced the gene for sterol 14α-demethylase (CYP51), and measured the expression of CYP51 and homologs of four putative efflux transporter genes, which we identified in the E. necator transcriptome. Sequence variation in CYP51 was relatively low, with sequences of 40 U.S. isolates identical to the reference sequence. Nine U.S. isolates and five from Chile carried a previously identified A to T nucleotide substitution in position 495 (A495T), which results in an amino acid substitution in codon 136 (Y136F) and correlates with high levels of azole resistance. We also found a nucleotide substitution in position 1119 (A1119C) in 15 U.S. isolates, whose mean EC50 value was equivalent to that for the Y136F isolates. Isolates carrying mutation A1119C had significantly greater CYP51 expression, even though A1119C does not affect the CYP51 amino acid sequence. Regression analysis showed no significant effects of the expression of efflux transporter genes on EC50. Both the Y136F mutation in CYP51 and increased CYP51 expression appear responsible for azole resistance in eastern U.S. populations of E. necator.
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van den Bosch F, Paveley N, van den Berg F, Hobbelen P, Oliver R. Mixtures as a fungicide resistance management tactic. PHYTOPATHOLOGY 2014; 104:1264-1273. [PMID: 25140387 DOI: 10.1094/phyto-04-14-0121-rvw] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We have reviewed the experimental and modeling evidence on the use of mixtures of fungicides of differing modes of action as a resistance management tactic. The evidence supports the following conclusions. 1. Adding a mixing partner to a fungicide that is at-risk of resistance (without lowering the dose of the at-risk fungicide) reduces the rate of selection for fungicide resistance. This holds for the use of mixing partner fungicides that have either multi-site or single-site modes of action. The resulting predicted increase in the effective life of the at-risk fungicide can be large enough to be of practical relevance. The more effective the mixing partner (due to inherent activity and/or dose), the larger the reduction in selection and the larger the increase in effective life of the at-risk fungicide. 2. Adding a mixing partner while lowering the dose of the at-risk fungicide reduces the selection for fungicide resistance, without compromising effective disease control. The very few studies existing suggest that the reduction in selection is more sensitive to lowering the dose of the at-risk fungicide than to increasing the dose of the mixing partner. 3. Although there are very few studies, the existing evidence suggests that mixing two at-risk fungicides is also a useful resistance management tactic. The aspects that have received too little attention to draw generic conclusions about the effectiveness of fungicide mixtures as resistance management strategies are as follows: (i) the relative effect of the dose of the two mixing partners on selection for fungicide resistance, (ii) the effect of mixing on the effective life of a fungicide (the time from introduction of the fungicide mode of action to the time point where the fungicide can no longer maintain effective disease control), (iii) polygenically determined resistance, (iv) mixtures of two at-risk fungicides, (v) the emergence phase of resistance evolution and the effects of mixtures during this phase, and (vi) monocyclic diseases and nonfoliar diseases. The lack of studies on these aspects of mixture use of fungicides should be a warning against overinterpreting the findings in this review.
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Lucas JA, Hawkins NJ, Fraaije BA. The evolution of fungicide resistance. ADVANCES IN APPLIED MICROBIOLOGY 2014; 90:29-92. [PMID: 25596029 DOI: 10.1016/bs.aambs.2014.09.001] [Citation(s) in RCA: 228] [Impact Index Per Article: 22.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Fungicides are widely used in developed agricultural systems to control disease and safeguard crop yield and quality. Over time, however, resistance to many of the most effective fungicides has emerged and spread in pathogen populations, compromising disease control. This review describes the development of resistance using case histories based on four important diseases of temperate cereal crops: eyespot (Oculimacula yallundae and Oculimacula acuformis), Septoria tritici blotch (Zymoseptoria tritici), powdery mildew (Blumeria graminis), and Fusarium ear blight (a complex of Fusarium and Microdochium spp). The sequential emergence of variant genotypes of these pathogens with reduced sensitivity to the most active single-site fungicides, methyl benzimidazole carbamates, demethylation inhibitors, quinone outside inhibitors, and succinate dehydrogenase inhibitors illustrates an ongoing evolutionary process in response to the introduction and use of different chemical classes. Analysis of the molecular mechanisms and genetic basis of resistance has provided more rapid and precise methods for detecting and monitoring the incidence of resistance in field populations, but when or where resistance will occur remains difficult to predict. The extent to which the predictability of resistance evolution can be improved by laboratory mutagenesis studies and fitness measurements, comparison between pathogens, and reconstruction of evolutionary pathways is discussed. Risk models based on fungal life cycles, fungicide properties, and exposure to the fungicide are now being refined to take account of additional traits associated with the rate of pathogen evolution. Experimental data on the selection of specific mutations or resistant genotypes in pathogen populations in response to fungicide treatments can be used in models evaluating the most effective strategies for reducing or preventing resistance. Resistance management based on robust scientific evidence is vital to prolong the effective life of fungicides and safeguard their future use in crop protection.
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Affiliation(s)
- John A Lucas
- Department of Biological Chemistry and Crop Protection, Rothamsted Research, Harpenden, UK
| | - Nichola J Hawkins
- Department of Biological Chemistry and Crop Protection, Rothamsted Research, Harpenden, UK
| | - Bart A Fraaije
- Department of Biological Chemistry and Crop Protection, Rothamsted Research, Harpenden, UK
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