ABSTRACTS

 

Innovative approaches to sustainable pest management in UK agriculture

Gideon Henderson

Chief Scientific Adviser, Defra

 

In order to support food security, farmers need to have access to a wide array of tools to manage pests, weeds and diseases. To minimise the harms from pesticides, we are encouraging farmers and growers to work holistically and use a diverse set of integrated pest management strategies, which will mean that chemical control can still be used but in a more targeted manner, enabling the chemistry to remain effective for longer before resistance develops. At Defra, we understand the multiple challenges that farmers face and the importance of cutting-edge scientific research in understanding the risks from pesticide resistance and new pest pressures and in developing the tools to manage these effectively.

 

Putting resistance management into action: An industry perspective

Andy Ward

CropLife RMPT

Resistance management needs to be based in excellent research but ultimately it needs to be implemented by farmers across the globe. Farmers need to buy into resistance management, with a belief in why it is needed and a clear understanding of how it can be implemented.

CropLife International is an association of multinational companies involved in research and development in plant sciences. It represents a global structure and member companies for whom resistance management is a key tool for sustainable crop protection with both pesticides and plant biotechnology. CropLife has been promoting a systems approach to resistance management, in partnership with key organisations.

A key pillar of CropLife’s strategic approach has been the inclusion of Mode of Action (MoA) icons and information on pesticide labels. These simplify the choice of pesticides for rotations or mixes for resistance management. Globally there has been a significant growth in MoA labelling and countries with mandatory MoA labelling requirements. Stewardship has been supporting this label information through considering key influences on farmer behaviour, including the cost and benefits of implementing resistance management and behavioural insights that should make outreach more effective.

 

Organophosphate resistance in Myzus persicae: exploring new discoveries in the genomic era

Troczka BJ¹, Singh KS¹, Zeng B¹, Hunt B¹, Field L², and Bass C¹.

¹ College of Life and Environmental Sciences, Biosciences, University of Exeter, Penryn Campus, Penryn, Cornwall, UK.

² Protecting Crops and the Environment, Rothamsted Research, Harpenden, UK.

b.troczka@exeter.ac.uk and c.bass@exeter.ac.uk

Over 30 years ago the molecular mechanisms of organophosphate tolerance in peach potato aphid Myzus persicae, became one of the best-studied examples of insecticide resistance in a crop pest. A series of publications, many of which came from Rothamsted Research, identified both the target site polymorphism and a metabolic component involving two closely related carboxylesterase genes called E4 and FE4. Subsequent molecular characterization at the time pinpointed the mechanism of resistance to an increase in gene copy number and changes in methylation for either E4 or FE4. However, the specific mechanism(s) by which these genes were amplified was never elucidated. The evolution of whole genome and transcriptome sequencing technologies created an opportunity to revisit this old story and fill the knowledge gaps which could not be addressed at the time. Thanks to access to over 100 live aphid clones with various levels of esterase resistance, we have combined the latest advances in long-read DNA sequencing, whole genome methylation calling and copy number estimation to gain a better understanding of how the esterase resistance emerged and is regulated in Myzus persicae.

 

The K⁺/Cl^- Cotransporter Represents a Putative Target to Reduce Resistance to Dieldrin (rdl)

 

Daniel R. Swale 

Emerging Pathogens Institute, Department of Entomology and Nematology, University of Florida, Gainesville, FL, 32610 

E-mail: dswale@epi.ufl.edu 

The γ-aminobutyric acid (GABA) receptor and GABA-receptor-chloride-channel (GRCC) complex is an established insecticide target, yet target site mutations in rdl, the gene encoding GABA-R, threaten the utility of GABAergic insecticides.  We defined the functional interplay between the GABA_A receptor and K⁺/Cl^- cotransporter (KCC) as a putative mechanism to reduce rdl phenotypes.  KCC concomitantly extrude K⁺ and Cl^- from the neuron to produce low intracellular Cl^- levels and enable inhibitory synaptic signaling through inward flux of Cl^-. Our data show that CNS-specific ablation or pharmacological inhibition of Drosophila KCC increased CNS spike discharge frequency and reduced GABA potency by 3-fold.  Further, KCC inhibitors at an EC₁₀ increased sensitivity of the Drosophila CNS to dieldrin by 4-fold that verified functional coupling of KCC to GRCC. Co-treatment of a KCC inhibitor (EC₁₀) and dieldrin increased the CNS firing rate by 70% in flies carrying rdl mutations but did not alter the firing rate in susceptible flies, which suggests KCC inhibition may rescue rdl phenotypes.  Indeed, toxicity bioassays with rdl-carrying Drosophila showed co-treatment of dieldrin with KCC inhibitors reduced the resistance ratio to 7-fold compared to 90-fold with dieldrin alone.  These data indicate KCC represents a putative target to mitigate resistance phenotypes to GABAergics.

 

The delay in confirming QoI-resistance in Puccinia horiana in Japan: overlooking risks beyond the G143A and F129L mutations

Y Matsuzaki 

Health and Crop Sciences Research Laboratory, Japan 

E-mail: matsuzakiy2@sc.sumitomo-chem.co.jp 

Resistance to QoI fungicides, conferred by target site mutations, is widely recognized among various pathogen populations. The major mechanisms of resistance are the G143A mutation in highly resistant strains and the F129L mutation in moderately resistant strains. Although the G137R mutation plays a minor role, it is frequently mentioned in the literature. In Japan, chrysanthemums account for 40% of ornamental plant production. White rust, caused by Puccinia horiana, has consistently been the most problematic pathogen for growers. Despite their efforts to adopt an IPM approach, the application of fungicides remains necessary, and the number of spraying is quite high. As a result, this species has become a hotspot for fungicide resistance among crop pathogens in the country. By around 2010, several years after the initial use, some farmers had already reported poor efficacy and suspected QoI resistance. Nevertheless, researchers could not confirm these suspicions because they did not detect the G143A, F129L, or G137R mutations and faced difficulties in obtaining reference-sensitive isolates of this obligate parasite. In 2019, resistance mediated by several mutations, initially identified in phytopathogens, was confirmed. This story, along with a cautionary note for fungicide researchers, will be presented.

 

Counteract Herbicide Resistance through Herbicide Selectivity: A Case Study on Selective Herbicide Safening in Arabidopsis thaliana

N, Onkokesung^1$, G, Pingarron-Cardenas^1#, A, Goldberg-Cavalleri¹, G, Lange², J, Dittgen³, and R, Edwards<sup>1

1</sup>Agriculture, School of Natural and Environmental Sciences, Newcastle University, Newcastle Upon Tyne, UK

² Bayer AG, Crop Science Division, Computational Life Sciences, Frankfurt, Germany

³ Bayer AG, Crop Science Division, Weed Control Research, Frankfurt, Germany

$Present Address: Bayer AG, Crop Science Division, Weed Control Research, Frankfurt, Germany

^# Present Address:  Department of Plant Sciences, University of Cambridge, Cambridge, UK.

nawaporn.onkokesung@bayer.com

There are more than 300 weed species that confirmed to develop resistance to multiple herbicides. To enable the diversification of herbicides to counteract resistance weeds, the herbicide selectivity in crops is a crucial factor. Safeners have long been used to facilitate herbicide selectivity by enhancing the expression of detoxifying enzymes such as glutathione transferases (GSTs) in monocot crops.  Even though safeners are known to induce the expression of detoxification genes in dicots, safeners do not protect dicot crops from herbicide toxicity. The aim of this study is to understand the cause of safener failure to protect dicot species which could then lead to the development of effective dicot safeners.  Using the model dicot Arabidopsis thaliana and the safener isoxadifen-ethyl (IDF) as a test system, seedlings and root cultures were treated with IDF to test for any enhancement in GST-mediated metabolism of the herbicides flufenacet and S-metolachlor. The combined analysis of transcript expression, herbicide metabolisms, enzymatic reactions and phenotyping of T-DNA insertion Arabidopsis mutant plants confirmed the importance roles of GSTU7 in the detoxification and safening toward flufenacet in Arabidopsis.  Our study demonstrates that safening effect in dicot can be achieved in the more restrict manners than those in monocot species. 

 

"Exploring the Resilience and Adaptability of Agricultural Weeds"

MacGregor, D R

Protecting Crops and the Environment, Rothamsted Research, UK 

Dana.MacGregor@rothamsted.ac.uk
 

Among the various traits exhibited by weeds, resilience and adaptability enable weeds in the agri-environment to withstand or rapidly adapt to both human-imposed control methods and environmental challenges such as abiotic or biotic stresses. Despite their importance, our understanding of the molecular mechanisms underlying either of these traits remains limited. Our research aims to address this knowledge gap through physiological, molecular, and genomic analyses of blackgrass as well as other globally problematic weeds. We quantify and compare the physiological traits and transcriptomic or metabolic pathways that give weeds their competitive edge over the crops they infest. We functionally validate interesting targets including by transiently manipulating gene expression in planta. We undertake comparative genomics using genomes we have sequenced, both the Mendelian-inherited chromosomes and extra-chromosomal circular DNA. Together, these approaches give us a detailed understanding of the mechanism(s) weeds use to withstand the challenges of the agri-environment. Through our molecular studies in agricultural weeds, we aim to both pinpoint vulnerabilities that can be targets for sustainable weed management and uncover the secrets of weed’s resilience and adaptability, thus providing valuable insights for safeguarding sympatric crops against future challenges, including from the weeds themselves.

 

Multi-drug resistance in the fungal wheat pathogen Zymoseptoria tritici: a hint to complex mechanisms

P. Simon-Leclaire¹, E. Neau^1,2, A. Lalève¹, and S. Fillinger<sup>1,*

1</sup> BIOGER, University Paris-Saclay, INRAE, Palaiseau, France

² University Paris-Saclay, Gif-sur-Yvette, France

*sabine.fillinger@inrae.fr

The agricultural sector faces increasing development of fungicide resistance in Zymoseptoria tritici, the agent of septoria leaf blotch in wheat. Since the early 2010s, strains with 'Multi-Drug Resistance' (MDR) phenotype have been detected in natural populations. This phenotype is associated with the overexpression of the membrane efflux pump gene MFS1 due to three distinct promoter inserts, resulting in increased efflux of fungicides. A Z. tritici population survey for MDR strains in 2020/21 led to the isolation of new MDR strains whose resistance profiles differ from previous field isolates and transgenic constructs indicating that additional mechanisms to MFS1 promoter inserts may be at play.

Experimental evolution studies have also led to the selection of MDR strains unlinked to MFS1 overexpression. To elucidate whether increased efflux is involved in these phenotypes, efflux tests were carried out on a selection of MDR isolates. The majority of the studied isolates exhibited an increase in comparison to the ancestor strain suggesting that their MDR phenotype may be attributed to increased fungicide efflux. Other isolates showed different phenotypes, indicating the involvement of alternative MDR mechanisms. Whole-genome sequencing revealed unknown genes potentially involved MDR. The involvement of a previously uncharacterized transcription factor in MDR will be presented.

 

Genetics of insect resistance to Vip3Aa

 

Zhenxing Liu, Chongyu Liao, Luming Zou, Minghui Jin, Yinxue Shan, Yan Peng, Wenhui Wang, Huihui Zhang, Hui Yao, Lei Zhang, Peng Wang, Zhuangzhuang Liu, Na Wang, Yutao Xiao, Yudong Quan, Anjing Li, Kaiyu Liu, Kongming Wu, Bruce Tabashnik,

and David G. Heckel 

AGIS, Chinese Academy of Agricultural Sciences, Shenzhen, China

Central China Normal University, Wuhan, China

IPP, Chinese Academy of Agricultural Sciences, Beijing, China

University of Arizona, Tucson, USA

Max Planck Institute for Chemical Ecology, Jena, Germany

E-mail: heckel@ice.mpt.de

 

The VIP (vegetative insecticidal proteins) toxins from Bacillus thuringiensis kill insects via different pathways compared with the Cry toxins.  Vip3Aa is deployed in transgenic crops as a backup against pest evolution of Cry toxin resistance, and is currently effective against the fall armyworm, Spodoptera frugiperda.  However, Vip3Aa-resistant strains of several pest species are now known.  Two different mutations associated with resistance to Vip3Aa have been reported from lab-selected strains of invasive S. frugiperda from China.  One is a change in the promoter sequence of SfMyb, a transcription factor that apparently controls the expression of protein binding targets of Vip3A in the midgut.  Another is insertion of a transposable element that disrupts the coding sequence of SfCHS2, the chitin synthase responsible for chitin production in the peritrophic matrix in the midgut. Knockouts of the chitin synthase gene conferred resistance to Vip3Aa in S. frugiperda and two other lepidopteran pests. We expect that mutations conferring S. frugiperda resistance to Vip3Aa occur in loci other than SfMyb and SfCHS2. Anticipating and managing Vip3Aa resistance is important for sustainable pest control, especially with field-evolved resistance to Cry toxins conferred by a dominant mutation affecting tetraspanin and associated with increased protease activity. 

 

A new player involved in metabolic resistance in Echinochloa crus-galli

Hinata Ishizawa^1*, Masumi Ishizaka², Chiharu Akimoto-Tomiyama³, Masaki Endo³, Rintaro Suzuki², Akira Uchino⁴, and Satoshi Iwakami^5*

¹Graduate School of Agriculture, Kyoto University, Japan, ² Research Center for Advanced Analysis, NARO, Japan, ³Institute of Agrobiological Sciences, NARO, Japan, ⁴Central Region Agricultural Research Center, NARO, Japan, ⁵Graduate School of Agriculture, Tokyo University of Agriculture and Technology, Japan

*iwakamis@go.tuat.ac.jp

Metabolic resistance is the common mechanism of herbicide resistance in grass weeds. However, the molecular mechanism behind this resistance remains poorly understood. This study aimed to elucidate the resistance mechanism of a Echinochloa crus-galli var. formosensis line (Ecf108) that exhibits resistance specifically to an acetyl-CoA carboxylase (ACCase) inhibiting herbicide cyhalofop-butyl. LC-MS/MS analysis revealed an enhanced metabolism of cyhalofop-acid in Ecf108. Two rounds of RNA-seq analyses were conducted using multiple E. crus-galli lines collected from various regions in Japan, identifying 62 highly expressed genes in Ecf108. Among the candidate genes, EcCBR1 conferred resistance to cyhalofop-butyl in rice calli. Since CBR1 exists as two copies in diploid grass genomes, we used CRISPR/Cas9 to individually knock out the homologs of EcCBR1 in rice. The resulting mutants showed increased sensitivity to cyhalofop-butyl, indicating the crucial role of these genes in plant metabolism of cyhalofop-butyl. Further investigations are underway to explore the involvement of EcCBR1 in the evolution of cyhalofop-butyl resistance in E. crus-galli.

 

Searching for new “biofungicides” based on oligonucleotides for the control of fungal diseases

Dolores Fernández-Ortuño^1,2

¹Dpto. de Microbiología, Facultad de Ciencias, Universidad de Málaga, Málaga, Spain;

²Dpto. de Microbiología y Protección de Cultivos, Instituto de Hortofruticultura Subtropical y Mediterránea (IHSM-UMA-CSIC) “La Mayora”, Campus de Teatinos, Málaga, Spain 

Email: dfernandez-ortuno@uma.es

 

Botrytis cinerea and Podosphaera xanthii, the causal agents of the gray mold and the cucurbit powdery mildew diseases, respectively, are limiting factors of horticultural crops production worldwide. Their control is very dependent on the application of commercial fungicides; however, both have developed high levels of resistance to the most chemical classes, a fact that has been widely demonstrated in Spain. In addition to this problem, the recent European Green Deal will be reduced the diversity of fungicides available to growers by 50% in 2030. For this reason, alternative control tools and molecules with fungicide activity are needed. In our research group, the efficacy of the emerging RNA interference (RNAi) strategy, called "spray-induced gene silencing" (SIGS), and the use of aptamers have been checked as sustainable solutions to be used into the integrated management programs of both diseases. For this purpose, several double-stranded RNA (dsRNAs) and two aptamers, involved in the virulence/pathogenicity of both pathogens, have been designed. To improve their applications under field conditions, their nanoencapsulation have also be carried out. The progress made in our research works will be presented.

These works have been funded by the PAIDI 2020 (PY20_00048) and by MICIN (PID2019-107464RB-C21, PDC2021-121373-C21, PID2022-136240OB-C21/AEI/10.13039/501100011033/ FEDER, UE).

 

Sub-lethal insecticide stress alters epimutation rate and transposable element expression, but not mutation rate, in Myzus persicae

 

BJ Hunt^1*, KS Singh¹, BJ Troczka¹, J Mackisack¹, E Randall¹, M Mallott¹, T Baril¹, J Galbraith¹, B Kuijper¹, R Nauen², A Hayward¹ and C Bass¹

1 Centre for Ecology and Conservation, University of Exeter, UK.

2 Crop Science Division, Bayer AG, Germany

*Corresponding author: b.hunt2@exeter.ac.uk

A long-standing hypothesis proposes that exposure to low doses of pesticides may increase the mutation rate in pest genomes and consequently accelerate the evolution of resistant phenotypes. Yet the impact of pesticide-induced stress on the mutation rate of insects has not been empirically tested. We ran a two year long mutation accumulation experiment using the global pest aphid Myzus persicae to interrogate spontaneous genetic and epigenetic mutation rates in insecticide-exposed and unexposed aphid lines. Our data reveal that long-term exposure to sub-lethal concentrations of the neonicotinoid insecticide imidacloprid over 50 generations does not increase genetic mutation rate. Instead we find that imidacloprid exposure results in a significantly lower epimutation rate and enhances the transcriptional activity of transposable elements, as well as inducing the downregulation of numerous genes related to neuronal function and development. Our findings challenge the proposed link between pesticide exposure and the rate of mutation and suggest that a more nuanced view of this hypothesis is required.

 

Tiny tech, big impact: Long read sequencing in the fight against fungicide resistance

Zulak KG¹, Farfan-Caceres L¹, Turo C¹, Mair, WJ¹, Knight NL¹², and Lopez-Ruiz FJ¹

¹Centre for Crop and Disease Management, School of Molecular Life Sciences, Curtin University, Australia

²Centre for Crop Health, University of Southern Queensland, Australia

katherine.zulak@curtin.edu.au

Uncovering the molecular mechanisms of fungicide resistance along with rapid, simple and scalable detection and monitoring programmes are essential to keep up with the rapid pace of resistance evolution. We used the Oxford Nanopore Technologies MinION DNA sequencer to characterise a resistance mechanism involving copy number changes of the demethylase inhibitor target gene Cyp51A in the barley pathogen Pyrenophora teres f. teres (Ptt). Our analysis revealed a long repetitive tandem sequence in which Cyp51A copies were found in alternation with transposable elements. These tandem sequences also contained predicted effector-like genes that are currently being characterised. Furthermore, we developed a simple and effective monitoring pipeline to detect both known and new mutations in Cyp51A in Ptt, P. teres f. maculata and a hybrid of these two forms, with SNP level accuracy. Our approach detects both known and novel mutations in both the promoter and coding sequence of Cyp51A, increasing the simplicity, accuracy and ease of resistance detection. Long read sequencing has enabled new insights into the molecular mechanisms of fungicide resistance in P. teres and effective ways of monitoring its evolution.

 

Identification of a single glutathione-S-transferase gene associated with atrazine resistance in Amaranthus palmeri

 

S. S. Kaundun* ¹, S.-J. Hutchings¹, L. Jackson¹, R. Dale¹, M. Simoes¹, S. Widdison², M. Braziers-Hicks¹, J. Downes¹ and E. Mcindoe¹

 

Herbicide Bioscience¹ and General Bioinformatics², Syngenta Jealott’s Hill International Research Centre, Bracknell, RG42 6EY, United-Kingdom

*Email address: deepak.kaundun@syngenta.com

 

Atrazine is an important herbicide for controlling Amaranthus species in corn-soybean production systems in the Americas. Excessive use of the herbicide, however, has resulted in resistance evolution in a number of A. palmeri populations. Analysis of the psbA gene has shown that resistance to atrazine in the A. palmeri populations is not due to a target-site mutation. Here, we have carried out an RNA-seq experiment to determine the gene(s) involved in non-target-site-based resistance (NTSR) to atrazine. Whole transcriptome data from nine sensitive and ten atrazine-resistant US populations identified a single Phi-class glutathione-S-transferase gene (denoted ApGSTF1) that was constitutively over-expressed several hundredfold in the resistant as compared to the sensitive populations. Heterologous expression of ApGSTF1 in E. coli/tobacco further confirmed the involvement of the enzyme in atrazine resistance. ApGSTF1 also conferred resistance to the chlorotriazine herbicides terbutylazine and cyanazine but not to the other photosystemII herbicides tested. This study identified the first fully validated gene that endows non-target-site resistance to triazine herbicides in the increasingly problematic Amaranthus palmeri species. Development and implementation of an Elisa-specific assay will determine the prevalence of ApGSTF1 in a large number of A. palmeri samples from Mid-Western USA.

 

Sublethal exposure to pesticides and transgenerational plasticity in insect pest Leptinotarsa decemlineata

L. Lindström
Department of Biological and Environmental Science, University of Jyväskylä. Finland
leena.m.lindstrom@jyu.fi

While the resistance models often highlight genetic mutations at the target site as the cause of resistance, recent evidence suggests that polygenic resistance involving different behavioral and physiological adaptations, may better explain regional differences in insecticide resistance. For example, despite a similar frequency of resistance-associated alleles in the Ldace2 gene the Colorado potato beetles (Leptinotarsa decemlineata) from Vermont, USA are 8-16 times more resistant against insecticides than the beetles from Belchow, Poland. Vermont population achieve this resistance through additional amino acid replacements in another Ldace1 gene, increased Ldace1 gene expression, and reduced sensitive to acetylcholinesterase (AChE) inhibition by insecticides. In addition to strong directional selection by lethal dosages of insecticides, polygenic resistance can also be selected by mild sublethal insecticide or other pesticide exposure. This is because mild stress is known to affect the whole genome and many genes at the same time, thus selecting for overall performance. Sublethal insecticide exposure can have further transgenerational effects on fitness-related traits (survival and body mass). These findings highlight the complexity of resistance as it is a result of selection, genetic architecture, and stress tolerance. Understanding these processes is, however, crucial for effective pest management and sustainable agriculture.

 

Multiple Resistance of Important Oomycetes - An increasing threat for Resistance Management in times of Limited Chemical Options

Andreas Mehl

Bayer AG, Crop Science Division, R&D, Germany

andreas.mehl@bayer.com 

Plasmopara viticola and Phytophthora infestans represent the most devastating grapevine and potato diseases caused by Oomycetes. Consequently, grapevine downy mildew and potato late blight control mostly relies on compounds being developed to specifically inhibit Oomycota species. Important active ingredients belong to the compound group of phenylamides, benzamides, CAAs, QiIs, QioSIs, carbamates, cyanoacetamide-oximes, and OSBPIs. For sound disease- and resistance management, todays´ spray schedules usually include a broad diversity of the above mentioned chemical control options, in-line with FRAC use guidelines. However, according to recent FRAC reports [1], resistance cases have been meanwhile reported for the majority of effective oomyceticides, and latest sensitivity monitoring often show occurrence of isolates bearing resistance to multiple active ingredients and biochemical mode of action. Increasing knowledge in molecular biology and genome sequences of plant pathogens has enabled development of new detection and quantification methods for resistance, adding valuable insights to data from standard sensitivity test systems. Recent examples from resistance research with P. viticola and P. infestans are presented, outlining a lack of specific control solutions in certain grapevine and potato growing regions and the need for more, innovative chemical options with new mode of action.

[1]       Anonymous, www.frac.info, 2024

 

Target-site resistance diagnosis reimagined: a new high-throughput method and its application to analyze hundreds of weed populations

 

U Lutz^1*, J Herrmann², J Wagner³, and D Weigel¹ 

¹ Max Planck Institute for Biology Tübingen, Germany

² Agris42 GmbH, Germany

³ Plant Pathology and Crop Protection, University of Göttingen, Germany 

^* Corresponding author: ulrich.lutz@tuebingen.mpg.de

Herbicide resistance in weeds is threatening crop yields worldwide. Molecular techniques help to diagnose target-site resistance (TSR), a main mechanism for herbicide resistance. However, current methods are costly, slow, and lack scalability, limiting full assessment of resistance in weed populations. Also, because of high false negative rates, low TSR levels may go undetected. We present a cost-efficient, highly scalable method that combines sample pooling with compact and affordable Nanopore sequencing. We investigated the quantitative and qualitative distribution of TSR in hundreds of Alopecurus myosuroides (blackgrass) populations in Germany and Eleusine indica (goosegrass) populations in Mauritius. To estimate how TSR frequencies change in A. myosuroides after a single herbicide treatment in real-world conditions, we collaborated with German farmers to sample before and after spring application. Furthermore, we present the method's power to assess homeologue-specific TSR allele frequencies in polyploids and a workflow to detect low TSR in seed samples of commercial Lolium spp., which could represent a possible source of dispersal of resistant weedy Lolium spp. As herbicide resistance management becomes more complex, high-resolution diagnosis becomes increasingly important. We are confident that our new method can make significant contributions to addressing herbicide resistance in both research and the crop value chain.

 

Genetic architecture of pesticide resistance in the mite, Halotydeus destructor, from its invasive Australian range

JA Thia^1*, ND Young², S Sumanam², RB Gasser², PA Umina³, and AA Hoffmann¹ 

¹ School of BioSciences, University of Melbourne, Australia

² Department of Veterinary BioSciences, University of Melbourne, Australia

³ Cesar Australia, Australia

^* Corresponding author: joshua.thia@unimelb.edu.au

The redlegged earth mite, Halotydeus destructor (Tucker 1925: Trombidiformes, Penthaleidae), is a major pest of Australia’s grain and pasture crop industries. Native to South Africa, this mite invaded Australia in the 1920s and was managed very successfully with chemical pesticides for many decades. However, since the early 2000s, resistance to organophosphate and pyrethroid pesticides has increased and spread throughout Australia, making it increasingly difficult to control this pest. Genomic approaches and a chromosome-level reference assembly have been paramount in characterising the genetic architecture of pesticide resistance and the dynamics of resistance evolution in H. destructor. We show that populations from across Australia can evolve resistance by combining target-site mutations, copy number variation, and other genetic mechanisms. Moreover, population genomic analyses suggest that resistance often evolves independently in local populations and is unlikely to be spread via dispersal. These findings have contributed to increased awareness that local strategies matter and the importance of farm-level management. Our findings have also been instrumental in developing molecular diagnostic tools that will facilitate resistance monitoring in this invasive mite pest.

 

Quantifying selection on and origins of resistance mutations through space and time

Kreiner, Julia

Ecology & Evolution, University of Chicago, United States

kreiner@uchicago.edu

The evolution of resistance in response to herbicides is a striking example of repeated, human-induced evolution. Nonetheless, the evolutionary genetic mechanisms underlying their origins and rate of spread have been largely unquantified over spatial and temporal scales. Towards this goal, we have been studying one of the most problematic weeds in the Midwestern US, common waterhemp. Combining paired natural-agricultural sampling from the present day with sequences from historical specimens, we demonstrate the remarkable rate of resistance evolution over the last two centuries, even in comparison to newly pinpointed agriculturally adaptive alleles. Over the same period, I show concurrent shifts in population size and structure—highlighting a strong link between demographic and selective contemporary change. I will then discuss how this rate of evolution is in part driven by multiple origins of resistance, regardless of the complexity of mutations, from single nucleotide polymorphisms to structural variants. These approaches can help diagnose the spatiotemporal scales at which resistance management should occur across complex landscapes

 

Updating the principles of resistance management: a new theoretical framework

Madgwick, P. G.^1* and Kanitz, R.²

¹ Syngenta, Jealott’s Hill International Research Centre, Bracknell, RG42 6EY, UK.

² Syngenta Crop Protection, Rosentalstrasse 67, Basel, CH-4058, Switzerland.

^* To whom correspondence may be addressed: Philip.Madgwick@syngenta.com

When building a resistance management plan, it is useful to work with clear and distinct evolutionary mechanisms for how resistance can be delayed. Resistance modelling in the 1980s was helpful in defining those mechanisms, which were influentially reviewed in the following decade to build a consensus on the principles of resistance management. Recent resistance modelling has challenged the consensus, bringing new approaches and considerations to resistance management. This work has also led to recent changes in resistance management policy (e.g. IRAC). Here, building on old and new publications, we provide a synthetic review of the evolutionary mechanisms that delay resistance. We propose an updated classification of the principles of resistance management. We discuss how these principles can complement and clash with one another in alternative strategies, including some are based on new approaches to resistance management. Overall, we show how these principles provide a rational framework for explaining how to design a resistance management plan to delay resistance evolution.

 

Adaptation of Ramularia collo-cygni towards SDHIs and DMIs

Kowalski P, Guschwa Z, Glaab A, Strobel D, Stammler G

BASF SE, Germany

Przemyslaw.Kowalski@basf.com

Ramularia leaf spot caused by Ramularia collo-cygni is a significant disease in barley, classified as a high-risk pathogen by the Fungicide Resistance Action Committee (FRAC). QoIs have been highly effective for Ramularia control, however resistance developed soon after market introduction with a rapid spread across Europe. Other groups of fungicides, such as SDHIs and DMIs have been also affected by adaptation to these modes of actions. The molecular mechanisms have been elucidated and the evolution of these and their effects on sensitivity loss have been intensively studied. There are several mutations causing SDH resistance with different levels of resistance. Mutations causing the strongest resistance are less frequent (H153R, G171D) and those causing low (N87S) to moderate adaptation (H146R) are dominating with regional differences. Although the outstanding efficacy of SDHIs may be diminished, they are still valuable tools for disease control and resistance management. Additionally, various CYP51-haplotypes have been identified which cause low or moderate adaptation towards DMIs. However, there is still significant disease control, e.g. by the recently introduced DMI - mefentrifluconazole. Most recent data on the evolution of SDH- and CYP51-haplotypes in Europe and effects of control strategies on disease control and mutation selection will be presented.

 

Characterization of multiple herbicide resistant populations of Amaranthus palmeri from Europe

 

A. Manicardi¹, G. M. Marin¹, J.M. Llenes², J.M. Montull¹, A.L. Simões Araujo⁴, T.A. Gaines⁴, J. Lozano Juste³ and J. Torra Farré¹

¹ Department of Forestry and Agricultural Science and Engineering, Universidad de Lleida, Lleida, España

² Weed Science Unit of the Plant Protection Service, DARP, Generalitat de Catalunya, Lleida, España

³ Instituto de Biología Molecular y Celular de Plantas (IBMCP), Universitat Politècnica de València (UPV), Consejo Superior de Investigaciones Científicas (CSIC), Valencia, España.

⁴ Colorado State University, Department of Agricultural Biology, Fort Collins, Colorado, USA

*E-mail: alfredo.manicardiudl.cat

Amaranthus palmeri ranks among the most problematic weed species in American crop fields and is now spreading across Europe. With resistant populations to ALS- and EPSPS-inhibitors already described in Spain, suspicion increasing regarding the presence of multiple resistance to both modes of action in local populations. Moreover, the evolutionary events leading to these herbicide resistances remain unknown. In dose-response experiments with glyphosate on two roadside Spanish populations, a high survival rate was observed at a dose of 400 g a.e. ha-1. These same populations also exhibit high resistance to ALS-inhibitors thifensulfuron-methyl, and low resistance to imazamox. Target-site resistance appears to be the most prominent mechanism in both treatments. Plants surviving glyphosate showed increased EPSPS copy number variations but no mutations in the target protein. Surprisingly, survivors of ALS inhibitor exhibited 9 different mutant alleles in codons: Pro-197, Asp-376, and Trp-574. Given the history of selection pressure and the high incidence of detected mutations, we suspect that these populations have evolved resistance to both MoA in the country of origin. Further study on the eccDNA sequence in both Spanish populations seems to reinforce this idea. The presence of A. palmeri populations with multiple resistance poses a high risk European crops production.

Keywords: Amaranthus palmeri, herbicide resistance, ALS, EPSPS, eccDNA.

 

Predicting fungicide resistance by experimental evolution

N J Hawkins

Plant Pathology, NIAB, UK

nichola.hawkins@niab.com

 

An important area of progress in resistance research in recent decades has been a gradual shift from reactive studies to a more pro-active approach. This includes monitoring for early shifts in sensitivity before resistance reaches a level where growers experience control failures, and the requirement for resistance risk assessments for new products so management guidelines can be adjusted accordingly.

 

Since fungicide resistance often arises from de novo mutations that would not be found through baseline screening, fungicide risk assessments often use artificial selection and mutagenesis. These studies can give a useful indication of overall resistance risk, but cannot always predict which of a range of mutations generated in vitro will emerge as significant resistant genotypes in the field. Furthermore, the predictability of resistance evolution in different pathogens in the field has varied greatly between different fungicide classes. In some cases, one or two key mutations have recurred across tens of pathogen species, whereas in others, a wide range of mutations has been reported between and within species. I am using experimental evolution to compare the evolutionary repeatability of resistance to different fungicide classes, and the role of different fungicide use scenarios in driving parallel or divergent evolutionary trajectories.

 

The evolutionary journey of herbicide resistant Alopecurus myosuroides from wild to weed

 

C. Neto and P. Neve 

Department of Plant and Environmental Sciences, University of Copenhagen, Denmark

ccn@plen.ku.dk

As a key weediness trait, herbicide resistance presents a unique opportunity to understand weediness evolution and the effects of strong anthropogenic selective pressures in rapid adaptation. In Europe, blackgrass (Alopecurus myosuroides) has become a major threat to crop yields, mainly due to the recent and rapid evolution of herbicide resistance. Here, we aimed at reconstructing its spread in European agricultural landscapes, to gain insight into its evolution from wild to weed. Exploiting a comprehensive collection of 65 wild and weedy populations, we traced blackgrass history in space and time: we conclusively pinpointed its origin to the Black Sea region and followed its spread across Europe, making use of both contemporary individuals and pre-Green Revolution germplasm. We showed that modern weedy European populations are genetically differentiated from native and past populations. Moreover, we shed light into the genetic basis of herbicide resistance in blackgrass, defined by an oligogenic architecture, and characterized by loci under positive selection. This distinctive system helps us to delve into fundamental questions in evolutionary quantitative genetics, providing insights into the genetic basis of adaptation to novel environments and into the evolutionary processes underpinning plant populations responses to strong anthropogenic pressures.

 

Development and Application of a Coupled Population Dynamics and Population Genetics Mathematical Model to Link Insecticide Selection, Fitness Costs and Vector Control.

N.P. Hobbs^1,2 and N.Chitnis^1,2

1.      Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Switzerland

2.      University of Basel, Switzerland

neil.hobbs@swisstph.ch

Insecticides, deployed as insecticide-treated nets and indoor residual sprays, are the primary tool available for the control of mosquito-borne diseases, especially malaria. There is a need to develop and evaluate insecticide resistance management (IRM) strategies to mitigate the impact insecticide resistance (IR) has on disease control. We present a coupled mosquito population dynamics and population genetics model, allowing for the simultaneous evaluation of both the ability of IRM strategies to manage IR but also to control mosquito populations.  The model is structured to include the mosquito life-stage, sex, genetics, behaviours, and the mating status of the female mosquito. Fitness costs are included by impacting life-history traits (egg batch size, developmental times, natural survival and mating success). We present simulations which consider both insecticide selection during vector control and the relaxation of selection pressure as may occur when insecticides are rotated out. The detrimental effects of IR on disease control are accelerated by selection on male mosquitoes, but are offset by maintaining high coverage of interventions. Fitness costs affect the frequency of IR over time when the insecticide selection is relaxed but depend on RS genotype fitness and the initial IR frequency. These are important considerations when planning insecticide rotations.

 

Droplet digital PCR: a new molecular approach for the detection and quantification of SDHI mutations in Stemphylium vesicarium

 

M.Menghini, I.M.Nanni, K.Gazzetti and M.Collina

Department of Agricultural and Food Sciences, University of Bologna, Italy

Corresponding author: marina.collina@unibo.it

Stemphylium vesicarium is the causal agent of several plant diseases as well as brown spot of pear (BSP), which is one of the most economically important fungal diseases in European pear-production areas. Different classes of fungicides to control BSP are available, among them we find Succinate Dehydrogenase Inhibitors (SDHIs) that are considered by the FRAC from medium to high risk of resistance. In this study, we set up a sensitive and accurate droplet digital PCR (ddPCR) protocol able to detect and quantify two mutations involved in the resistance of SDHIs, early discovered in our laboratory. For the first time, the determination of allele percentage and the frequency of a mutation involved in BSP was carried out by employing ddPCR. This molecular approach provides a rapid diagnostic tool able to detect very low substitution percentages, which is very useful for fungicide resistance detection at early stages, to better apply management strategies for the contrast of BSP disease.

 

Monitoring and management of herbicide resistance in Denmark

M. Sønderskov§, S. M. Mathiassen§, C. Fabricius⁑, P. H. Petersen⁑ and P. Kudsk§

§Agroecology, Aarhus University, Denmark

⁑SEGES Innovation P/S, Denmark

mette.sonderskov@agro.au.dk

There are widespread problems with herbicide resistance in Denmark, especially for grass weeds such as Lolium multiflorum and Alopecurus myosuroides, but also for several broadleaved weed species. A semi-randomised baseline study monitoring for resistance among eleven weed species with known resistance or under suspicion for evolving resistance were conducted in 2013-15. The survey was conducted in the light of a restructuring of the pesticide tax that significantly changed the price relations between herbicides with herbicide resistance prone and non-prone modes of action. The general knowledge on herbicide use pattern in Denmark had a clear relationship with herbicide resistance among key weed species. Five weed species where resistance was widespread were included in a follow-up study in 2021. Poa annua was added to the list of weed species in the 2021 study as several cases of resistance had been identified in the intervening years. Herbicide resistance is considered a major treat to crop productivity by the farming community and several projects involving farmers are ongoing to showcase diverse management strategies. The involvement of farmers and demonstration of integrated weed management are instrumental to support changes in cropping systems, thus preventing, and mitigating the development of resistance.

 

Update on Insecticide Resistance in UK Pests: are we all doomed?

Foster, S.P., King, L. and Williamson, M.S.

Rothamsted Research, Harpenden, AL5 2JQ, UK

The evolution and spread of insecticide resistance in agricultural and horticultural pests continues to threaten our ability to protect our crops and imposes increased selection pressures on the active compounds that remain in our armoury. In addition, European Legislation, for example, making widespread restrictions on the use of neonicotinoids as seed treatments on all outdoor crops, is only exacerbating this situation. As a result, continued monitoring of any changes in the sensitivity/resistance profile of insect pest populations is crucial if we are to communicate relevant, up-to-date information to agronomists, growers and government regulators on which insecticides will work and, importantly, which will not. This presentation will give a ‘whistle stop tour’ summarising the insecticide resistance profiles currently seen in a range of important UK pests (primarily aphids and beetles); information gained through work collaboratively funded by Agrochemical Companies, Commodity Boards, Agronomy Companies and Defra.

 

 

Management drives regional level spatial distribution of demethylase inhibitor fungicide resistance in Pyrenophora teres f. teres: insight from neighbour network analysis

 

Hodgson, L. M., Lopez-Ruiz, F. J., Gibberd, M. R., Thomas, G. J., Rakshit, S., and Zerihun, A.

Centre for Crop and Disease Management, School of Molecular Sciences, Curtin University, Australia

leon.hodgson@curtin.edu.au

Fungicide resistance in foliar fungal pathogens of annual crops is a growing global issue for crop protection. Broadscale empirical studies of the distribution of resistance can inform resistance management approach. Pyrenophora teres f. teres, the causal agent of net form net blotch disease on barley, which has developed a mutation of the Cyp51A allele (in the F489L position) that confers resistance to demethylase inhibitor fungicides, was used as a model system. The spatial distribution of resistance and covariate analysis were explored in a survey spanning 300 km² over a two-year period and captured 367 random, mixed population samples from 31 barley fields. Processed samples were analysed using digital PCR to determine the ratio of mutant to wild-type Cyp51A alleles, as frequency. We show the spatial distribution of a quantified frequency of fungicide resistance and present the first analyses of spatial dependency for fungicide resistance in a foliar fungal pathogen. Spatial network analyses of survey data identify host cultivar as a major factor affecting fungicide resistance distribution pattern. The identification of cultivar as a key driver of landscape fungicide resistance distribution provides the opportunity for tactical management choices to minimise spread.

 

Living Lab to promote innovation in weed management in Italian agricultural crops

 

Silvia Panozzo, Laura Scarabel, Maurizio Sattin and Donato Loddo 

Institute for Sustainable Plant Protection (IPSP) - National Research Council of Italy (CNR), Italy 

silvia.panozzo@cnr.it

The use of a collaborative approach among all interested stakeholders to encourage technological innovation within farms is the basis of the so-called Living Labs (LLs). In the frame of the National Center Agritech, Spoke 4, task 4.2.1 aims to create networks of researchers, farmers and stakeholders working together to develop and disseminate innovative practices for enhancing farms’ resilience in the climate change scenario. CNR research unit focuses on weed control with the aim to combine sustainability and effectiveness, decreasing the use of chemicals, preserving water, and keeping the carbon cycle balanced. The CNR-LL includes several farms distributed in North-eastern Italy, a national working group (GIRE, Italian Herbicide Resistance Working Group) and an agricultural consultancy company (Agrin). Two main approaches will be proposed to the farmers: 1) innovative management strategies addressing two topics, “water topic” will compare broadcast herbicide application and the band herbicide application and “carbon topic” will compare different managements for cover crop termination and cash crop sowing; 2) innovative agricultural machinery for weed control (e.g. weed wiper bars, weed trimmers, tools for the removal of weed inflorescences and/or seeds destruction). This should favor the implementation of alternative management strategies through a collaborative approach to increase sustainability and environmental protection.

 

Fungicide resistance stewardship: opportunities to identify and drive best practice

Fiona Burnett and Henry Creissen

Plant and Soil Science Department, Scotland’s Rural College (SRUC), UK

fiona.burnett@sruc.ac.uk

The holistic practices encompassed in integrated pest management (IPM) align well with the principals of fungicide resistance stewardship. Using crop management techniques which delay, prevent or avoid disease from occurring reduce reliance on fungicides. Within crop protection programmes, reduced usage of individual actives either through reduced dose or application number, or through the insertion of alternatives such as elicitors or biological control agents can further reduce selection pressure. However, despite convincing evidence that reduced reliance on fungicides can reduce the risk of resistance, the science is complex and there are still mixed messages on best practice, such that less than suboptimal practices persist. Recent research shows that IPM uptake amongst farmers increases with familiarity, and also increases where they have access to independent advice and research data. Large arable farms tend to score higher for uptake of IPM practices than smaller enterprises, which perhaps reflects a greater ability to attend to open days and knowledge exchange events.  The gap between higher and lower scoring farms represents an opportunity to drive the uptake of stewardship practices. Groups such as FRAG UK which gather and interpret resistance information and reach consensus views on best practice have an important role in this.

 

How we best manage resistance?  A case study with glyphosate and paraquat resistant Lolium rigidum

 

Roberto Busi and Ken Flower

Australian Herbicide Resistance Initiative, UWA School of Agriculture and Environment, University of Western Australia

roberto.busi@uwa.edu.au

In Australia, Lolium rigidum has evolved herbicide resistance to 12 different modes of action and the management of multiple resistant ryegrass is a costly challenge for grain growers.  Herbicides are sustainably used to remove exceptionally adaptable L. rigidum populations to protect grain crop yields in mechanized no-till systems but weed resistance evolution is an unceasing side effect. From 2022 six ryegrass populations with multiple resistance to glyphosate and paraquat (and clethodim) were detected in Western Australia.  Following the initial resistance characterization, two years of intense field research occurred at different locations (three field sites) and in parallel studies under controlled conditions were conducted across those three populations with dual resistance to glyphosate and paraquat with the clear aim to find cost-effective herbicide solutions.  The study documents a novel type of multiple resistance occurring in broadacre settings, initially selected on marginal areas (fencelines) and then spreading into the adjacent cropped paddock. This study demonstrates that a science-based choice and subsequent deployment of herbicide mixtures is an essential strategy to defeat weed resistance.  Our thought-provoking study suggests there is no resistance that can’t be managed by herbicide mixtures and useful insights are drawn towards herbicide efficacy stewardship and cost-effective weed resistance management.

 

Characterization of a multi-resistant field population of Plutella xylostella from Taiwan

J.L. Mugenzi, C. Zimmer, P. Heinimann, F. Granberg  and D. Souza

Bioscience, Syngenta, Switzerland

jean_leon.mugenzi@syngenta.com

The diamondback moth, Plutella xylostella, poses a significant global threat to crucifer crops and has become notoriously challenging to control due to widespread insecticide resistance. This study characterizes a field-derived strain of P. xylostella from Taiwan, assessing its resistance to various insecticides and genotyping known target site resistance mutations. The results reveal alarming levels of resistance, with the moth showing high levels of resistance to a broad range of commercial insecticides. However, the strain remained susceptible to isocycloseram (Plinazolin®). Genotyping results indicated high frequencies (over 70%) of pyrethroid and cyclodiene organochloride resistance-related mutations, moderate frequencies (40-50%) for acetylcholinesterase inhibitors and benzoylureas resistance mutations, and low frequencies (20%) for diamide and abamectin resistance mutations. These findings highlight the prevalence of multiple resistance, necessitating careful consideration in the selection of insecticides for managing P. xylostella in Taiwan and potentially offering insights for global pest management strategies. Going forward, integrated pest management approaches and the development of novel insecticides are crucial for addressing this pressing issue.

 

Integrated Approach for Potato Late Blight Resistance Management and Stewardship

Audrey Derumier, Lawrence Veryser and Gwenael Champroux

Certis Belchim, Belgium 

Audrey.derumier@certisbelchim.com, Lawrence.veryser@certisbelchim.com, Gwenael.champroux@certisbelchim.com 

In recent years, Europe has witnessed emergence of new strains of Phytophthora infestans exhibiting resistance to key fungicides, including fluazinam, CAA, and oxathiapiprolin. These resistances, combined with a lack of robust innovative solutions, represent a significant challenge to potato cultivation across the continent, threatening yield stability and necessitating urgent action in resistance management and stewardship strategies. An integrated approach combining field monitoring, laboratory studies, and predictive modelling to enhance late blight resistance stewardship is possible with collaboration between stakeholders. Field monitoring is employed to track the prevalence and distribution of different pathogen strains, providing crucial data for resistance management. Laboratory studies provide some valuable information to experiment the spread of resistance strains among other strains within the population of Phytophthora infestans. Furthermore, predictive modelling techniques are utilized to simulate the evolution of pathogen strains, allowing for proactive adjustments in management strategies. Recommendations for agronomic practices and crop protection products can be tailored based on the findings, emphasizing the importance of integrated pest management approaches. Overall, this comprehensive approach can offer insights into sustainable late blight resistance management, ensuring the longevity and efficacy of control measures while promoting environmental stewardship in potato cultivation.

 

The WHO’s “Global Plan for

Insecticide Resistance Management in Malaria Vectors”

 

Jo Lines

Department of Disease Control, London School of Hygiene & Tropical Medicine, UK
jo.lines@lshtm.ac.uk

This talk will describe some interesting aspects of the WHO’s “Global Plan for Insecticide Resistance Management in Malaria Vectors” (the GPIRM).  First, the circumstances and events justifying the policy will be outlined, including the scaling-up of effective malaria vector control in Africa, and the resulting impact on the malaria burden. Then the processes of consensus-building and policy development will be explained.     In terms of implementation, the policy has had some success in influencing the policies and practices of national malaria control programmes, and the roles of institutions such as the Global Fund and the President’s Malaria Initiative will be considered.    The talk will end with a discussion of the future of insecticidal malaria vector control, and its role in malaria elimination in Africa. 

 

Which resistance management strategies work against concurrent evolution of resistance to fungicides?

 

I Corkley^1,2,3, N D Paveley², F van den Bosch², A Mikaberidze³ and A E Milne¹

¹Net Zero and Resilient Farming, Rothamsted Research, United Kingdom; ²Sustainable Agricultural Systems, ADAS, United Kingdom; ³School of Agriculture, Policy and Development, University of Reading, United Kingdom

isabel.corkley@rothamsted.ac.uk

Resistance management tactics to slow selection for target-site resistance to a single fungicidal mode of action (MoA) are well-supported by modelling and experimental evidence. These tactics include minimising the dose and number of applications, and applying in mixture with a different MoA. The best strategies for managing resistance evolving ‘concurrently’ to two or more MoA at the same time are less clear: this situation introduces complex trade-offs. For crop pathogens such as Zymoseptoria tritici, multiple fungicide applications per year are often required to keep infection below damaging levels of severity. Use of mixtures may therefore require splitting the total dose of a fungicide across two or more applications, reducing the dose of each MoA per application but increasing the exposure time of the pathogen to the fungicide. We modelled the effect of dose-splitting on selection for fungicide resistance to a single MoA and found that it varies between metabolic and target-site resistance, and with fungicide efficacy and decay rates. We then explored concurrent evolution of resistance, and identified when it is better to mix two MoA (with dose-splitting) and when it is better to alternate.

 

Testing insecticide resistance management strategies

 

S. D White¹, D. J. Coston¹, S. P. Foster², B. Maddison³ and N. D. Paveley¹ 

¹ Sustainable Agricultural Systems, ADAS, UK

² Rothamsted Research, UK

³ Biotechnology, ADAS, UK 

sachadwhite@gmail.com 

Insecticide resistance management (IRM) guidance advocates that 1) alternation of modes of action (MoA) is the most effective IRM strategy, 2) insecticides should be used at the full label dose, and 3) mixtures of insecticides should include both mixture components at the doses used when applied solo. Mechanistic modelling of target-site resistance shows that, for most scenarios relevant to a wide range of crop pest species, 1) mixtures are likely to result in longer effective lives for insecticide MoAs than alternation, 2) resistance selection is minimised by using the lowest dose at which robust control can be obtained, and 3) adjusting the dose of mixture components to achieve the same combined efficacy as a solo product is a better IRM strategy.  Changes to longstanding guidance require empirical proof. This paper describes cage experiments carried out to test the model findings. Myzus persicae populations comprising four clones, with different combinations of two target-site resistance mechanisms, were tested with several IRM strategies. Changes in resistance frequency and population control over time were quantified. The presence of the clone resistant to both MoA negated IRM strategies.  In the absence of that clone, there was some evidence for faster selection with the ‘double-dose’ mixture.

 

Herbicide resistance stewardship. Contribution of mechanistic and random forest models to support diagnostic.

 

R., Beffa¹, J., Lepke² and O., Richter² 

¹Königsteiner Weg 4, 65835 Liederbach, Germany; ²Institute of Geoecology, University of Technology Braunschweig, Langer Kamp 19c, 38106 Braunschweig, Germany.

Email: roland.beffa@t-online.de

Weeds are one main threat impacting worldwide the production and the quality of food, feed, and fibers. Agronomy practices are essential for weed control, but chemical control remains necessary. Repetitive treatments of herbicides, especially when a similar mode of action is used, lead to the evolution of resistance. This is a particular concern due to the fact that very few new chemical families are brought to the market. In addition weeds can evolve several resistance mechanisms based either on herbicide target modifications (Target Site Resistance), or non-target modifications (Non-Target Site Resistance). Herbicides resistance diagnostics either in greenhouse or in the laboratory is time consuming, and costly. Prediction tools to evaluate the risk of resistance evolution will greatly help to choose the best IWM strategy adapted to the local field situation. These comprise classical simulation models combining population dynamics and genetics and, recently, artificial intelligence (AI) methods such as random forest. In that report both approaches are combined with the introduction of a non-target site resistance evolution in the mechanistic model. To this end, artificial data were generated by a mechanistic model and used as training data set for a random forest classifier. Field history information was obtained by interviewing farm managers. The data includes the field histories and resistance status of A. myosuroides and Lolium ssp. of 98 fields from Germany and 131 fields from France. With accuracies of about 80% the results obtained by the random forest method applied to model generated data and real field data respectively are well comparable. In addition the simulation model revealed the existence of a tipping point beyond which sensitivity cannot be restored. This is of particular interest in defining strategies to mitigate resistance evolution. Artificial intelligence predictions can be established without knowing the resistance mechanisms but needs significant number of field data to be accurate enough. Advantages and disadvantages of both approaches will be discussed also in term of friendly use for the customers, in particular farmers.

Key words: herbicide resistance, modelling, simulation models, artificial intelligence, grasses