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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
Faced with climate changes, pest pressure on plants is increasing and new pest complexes are appearing, for which plant protection solutions are not yet available. The reduction of anthropic pressure on agroecosystems requires a reduction in the use of chemical inputs and the promotion of biocontrol approaches. In this book, we present new advances on plant disease management that are emerging from research outputs. The ability of biocontrol products to directly (e.g. production of antimicrobial peptides or quorum quenching activities by microorganisms, use of plant or agro-industrial by-products as biopesticides, etc.) or indirectly (e.g. via the increase of plant defense or plant growth pathways) protect plants against pathogens and pests is also considered. We also address new strategies like the development of phage-based biocontrol products and those that consider the plant as a holobiont and plant microbiota as targets of biocontrol treatments. The important question of the current regulatory process needed to launch plant production products on the market is also addressed, such as methods to evaluate their environmental impact.
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Veröffentlichungsjahr: 2022
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Table of Contents
Cover
Title Page
Copyright Page
Introduction
1 Regulatory Aspects of Biocontrol
1.1. Regulatory definition of biocontrol
1.2. Current issues and limitations
1.3. A mixed evolution
1.4. Necessary evolutions
1.5. Conclusion
1.6. References
2 Biological Controls in Horticulture
2.1. Introduction
2.2. Biological controls in horticulture
2.3. Physiological trade-offs for growth and immunity
2.4. Eco-innovations and economic trade-offs
2.5. Challenges and perspectives
2.6. Concluding remarks
2.7. References
3 Development of Omics Tools for the Assessments of the Environmental Fate and Impact of Biocontrol Agents
3.1. Introduction: emergence of biocontrol agents and their risks
3.2. Evaluation methodologies: an overview
3.3. Limitations of classic methodologies
3.4. Omics: potential tools for risks assessment?
3.5. Perspectives
3.6. List of abbreviations
3.7. Acknowledgments
3.8. References
4 Plant Secondary Metabolites Mode of Action in the Control of Root-Knot Nematodes
4.1. Introduction
4.2. Recent research on the use of plant secondary metabolites to control
Meloidogyne
spp.
4.3. Conclusion
4.4. References
5 Agro-industrial By-products and Waste as Sources of Biopesticides
5.1. Introduction
5.2. Biopesticidal properties of pyrolysis products from agro-industrial waste
5.3. Biopesticidal properties of hydrolates: by-products of essential oil distillation
5.4. Biopesticidal properties of olive oil mill waste
5.5. Conclusion and future directives
5.6. Acknowledgments
5.7. References
6 Antimicrobial and Defense Elicitor Peptides as Biopesticides for Plant Disease Control
6.1. Introduction
6.2. Peptides of microbial origin
6.3. Peptides from plants
6.4. Peptides from animals
6.5. Synthetic peptides
6.6. Biotechnological production of peptides Heterologous expression in living systems as biofactories appears more
6.7. References
7 Biocontrol of Plant Pathogens via Quorum Quenching
7.1. Quorum quenching to counteract quorum sensing
7.2. Quorum sensing inhibitors
7.3. Quorum quenching enzymes
7.4. Quorum quenching biocontrol agents QQ activity may be considered as a trait to be searched for in identifying
7.5. Monitoring of quorum quenching biocontrol agents and activities
7.6. Biostimulation of quorum quenching
7.7. Management of quorum quenching treatments
7.8. Quorum quenching in biocontrol: perspectives
7.9. Acknowledgments
7.10. References
8 Phage-mediated Biocontrol Against Plant Pathogenic Bacteria
8.1. Introduction
8.2. Bacteriophages for plant health
8.3. Phage-based biocontrol regulations
8.4. Conclusions and perspectives
8.5. Acknowledgments
8.6. References
9 Microbiome-assisted Agriculture
9.1. Introduction
9.2. Microbiome-mediated benefits for plants
9.3. Chemical cues derived from plants and microbes guide microbiome assembly
9.4. Plant and soil microbiome engineering
9.5. Concluding remarks and future perspectives
9.6. References
List of Authors
Index
End User License Agreement
List of Tables
Chapter 2
Table 2.1
Some examples of biocontrol in horticulture
Chapter 3
Table 3.1
Summary of the reported genomics-based research works conducted in
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Chapter 5
Table 5.1
Nematicidal pyrolysis products from different agro-industrial wast
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Table 5.2
Relevant insecticidal pyrolysis bio-oils from different agro-indus
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Table 5.3
Nematicidal activity of hydrolate/hydrosol by-products from essent
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Table 5.4
Insecticidal activity of hydrolate/hydrosol by-products from essen
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Table 5.5
Nematicidal activity of olive oil mill wastewater
Table 5.6
Insecticidal activity of olive oil mill wastewater
Chapter 6
Table 6.1
Antimicrobial peptides produced by strains of bacteria and fungi t
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Table 6.2
Antimicrobial peptides (AMPs) that are active against plant pathog
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Table 6.3
Peptides of animal origin with activity against plant pathogenic f
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Table 6.4
Synthetic peptides and analogs active against plant pathogenic bac
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Chapter 8
Table 8.1
Proof of concept of phage biocontrol for crop protection during th
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Table 8.2
Phage biocontrol against plant pathogens: pros and cons
List of Illustrations
Introduction
Figure I.1
Necessary steps in the development of biocontrol agents (BCAs)
Chapter 2
Figure 2.1
Biocontrol and biostimulants can help plants cope with biotic and
...
Figure 2.2
Distribution of business names and active substances by leading g
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Figure 2.3
Trends of patent families over the period 1991–2018
Figure 2.4
Main patent assignees over the period 1991–2018
Chapter 3
Figure 3.1
Evolution of the number of articles holding the term “metabolomic
...
Figure 3.2
The environmental metabolic footprinting concept. Figure readapte
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Figure 3.3
The “resilience time” indicator. This example shows that the resi
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Chapter 6
Figure 6.1
Structures of antimicrobial and plant defense elicitor peptides.
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Figure 6.2
Workflow of the discovery and development of functional peptides
...
Chapter 9
Figure 9.1
The plant microbiome. This figure was created using Biorender.com
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Figure 9.2
Conceptual figure illustrating strategies for plant and soil micr
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Guide
Cover Page
Title Page
Copyright Page
Introduction
Table of Contents
Begin Reading
List of Authors
Index
Wiley End User License Agreement
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SCIENCES
Ecosystems and Environment, Field Director –Françoise Gaill and Dominique Joly
Environment, Natural or Anthropogenic Pressures,Subject Head – Denis Faure
Biocontrol of Plant Disease
Recent Advances and Prospects in Plant Protection
Coordinated by
Claire Prigent-CombaretBernard Dumas
First published 2022 in Great Britain and the United States by ISTE Ltd and John Wiley & Sons, Inc.
Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms and licenses issued by the CLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address:
ISTE Ltd27-37 St George’s RoadLondon SW19 4EUUK
John Wiley & Sons, Inc.111 River StreetHoboken, NJ 07030USA
www.iste.co.uk
www.wiley.com
© ISTE Ltd 2022The rights of Claire Prigent-Combaret and Bernard Dumas to be identified as the authors of this work have been asserted by them in accordance with the Copyright, Designs and Patents Act 1988.
Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s), contributor(s) or editor(s) and do not necessarily reflect the views of ISTE Group.
Library of Congress Control Number: 2022941466
British Library Cataloguing-in-Publication DataA CIP record for this book is available from the British LibraryISBN 978-1-78945-098-9
ERC code:LS6 Immunity and Infection LS6_8 Infectious diseases in animals and plants
IntroductionPromoting Biocontrol and Sustainable Crop Protection Strategies, a Major Challenge for the 21st Century
Bernard DUMAS1 and Claire PRIGENT-COMBARET2
1 LRSV, Toulouse University, France
2 EM, UMR 5557, Lyon 1 University, France
During the 20th century, in response to the need to significantly increase production, agriculture resorted to the massive use of chemical inputs (fertilizers and pesticides). This made it possible to provide crops with all the essential nutrients needed for their growth (nitrogen fertilizers, phosphorus, etc.) while effectively protecting them from diseases and pests (fungicides, insecticides, herbicides). Although these products have been extremely effective and have resulted in a significant increase in crop yield, their large-scale use has led, in some cases, to the degradation of soil quality and has had a dramatic impact on natural flora and fauna (a reduction in biodiversity, the appearance of resistant individuals, etc.). Today, the increased availability of better-quality food has made it possible to achieve food safety and has also provided customers with wide access to a healthy diverse diet. These beneficial effects have, however, come at the cost of adverse health effects associated with the use of certain inputs with a hazardous toxicological profile. As a result, the way in which we develop and use agricultural inputs has seen a major reorientation following a shift in policies to drastically reduce agricultural inputs originating from synthetic chemistry (including chemical fertilizers and phytosanitary products), which we have been systematically implementing for the last several years to focus on developing alternative solutions with a lower environmental impact. The main goal of these policies is the sustainable production of quality foods that are safe for both the environment and the consumer.
Twenty-first century agriculture must therefore face the added constraint of reducing environmental impacts in addition to ensuring adequate production capacity to maintain the viability of its economic model. There are enormous economic challenges to be addressed for developing a sustainable agriculture that also respects the environment. Today, consumers are increasingly aware of the need to produce healthy food albeit with a low environmental impact. To this end, they are increasingly turning to products from alternative systems; these may be products with zero residue specifications from organic farming, or local production sold via short supply chains. This calls into question our historical production model with respect to its choice of crop species, inputs used and marketing channels.
To address these new challenges, a significant research and development effort is needed to optimize and integrate new agronomic methods so that we can circumvent the massive use of non-natural products originating from so-called “conventional” synthetic chemistry. Such research involves setting up new farming practices (tillage, crop rotation, etc.) and the genetic selection of varieties that guarantee yield and improve resistance to stress and which are in symbiosis with soil microbial communities, while at the same time developing new inputs with a low environmental impact. In this context, the implementation of effective solutions as an alternative to “conventional” treatments will be decisive for the competitiveness of our current agricultural model.
One approach that is currently being developed is through the use of natural compounds to combat weeds, diseases and pathogens (biocontrol) and to optimize nutrition and plant development (biostimulant). For several years now, the application of these two types of products has seen a sharp increase, particularly in the context of organic farming. Manufacturers in this sector have set themselves the ambitious goal of capturing 30% of the crop protection market by 2030, which is in line with national public policies, notably in the European Union (using the strategy “Farm to Fork”, which aims for a 50% reduction in plant protection products and 25% conversion to organic farming by 2030 – https://ec.europa.eu/food/farm2fork_en). The major obstacle to achieving these ambitious objectives, however, remains identifying new active substances or living organisms of agronomic interest which are more environmentally friendly. Moreover, in order to exploit the potential of these active substances and provide solutions to ensure optimal crop protection while guaranteeing better yield, we also need to understand their mode of action in the complex environment that constitutes our agricultural system (Figure I.1).
Figure I.1Necessary steps in the development of biocontrol agents (BCAs)
The objective of this book is to gather works written by leading scientists in their fields in the form of chapters to illustrate the multifaceted aspects of the research devoted to finding new environmentally compatible solutions to protect plants against diseases, while maintaining crop yields. This book also addresses the important question of the current regulatory process needed to launch plant production products on the market (Figure I.1). We have chosen articles from research works presenting new advances on plant disease management through innovative strategies. Since an exhaustive panorama of biocontrol strategies is out of the scope of this book, certain topics such as the mechanisms involved in the protection of plants against insects by indirect action (e.g. the use of pheromones and kairomones and other natural defense stimulators) will not be covered in this book. However, the ability of biocontrol agents to protect plants against bacterial, fungal or oomycete pathogens or diseases triggered by insects or nematodes directly (e.g. by producing antimicrobial peptides, using the quorum quenching strategy with microorganisms, using plant or agro-industrial by-products as biopesticides, etc.) or indirectly (e.g. by increasing plant defense signaling pathways (via induced systemic resistance (ISR)), or by stimulating plant growth and development) will be described. We also want to address new strategies such as the development of phage-based biocontrol and those in which preventing pathogen-induced dysbiosis of plant microbiota is considered to be key to ensuring the overall health of the plant.
The different phases in the development of BCAs are identical to those when developing chemicals. The first phase is to identify candidates by screening biological collections that usually involve collaborative work between academic labs and industrial partners. At this stage, it is crucial to analyze the patentability of the selected candidates. The second phase concerns the initial development of BCAs, including the analysis of their activity on target crops and the evaluation of their industrial production feasibility. The knowledge acquired during phase I and II is essential for the subsequent development of the products. Phases I and II are intimately linked and only a few candidates are selected for phase III. Phase III (regulatory process), done on the main candidates, is probably the one that is the most expensive and time consuming. This phase involves toxicological analyses and several years of field tests to demonstrate the efficacy of the product. Finally, phase IV includes the final steps to launch the product on the market. Together, these phases need about 10 years and an investment of several hundreds of millions of euros to be completed. Even if the investment is mainly in phase III, regulations defined by authorities influence the decision to select a certain BCA (phase I) and to continue with its initial development (phase II). The positioning of the chapters in relation to these different stages is indicated on the right side of the figure.
A crucial step in introducing a plant protection product onto the market is the associated regulatory process, which directly impacts the investment needed to launch the product. The way in which this regulatory process is defined also influences the search for new active compounds in that those that have the greatest chance to be homologated will be preferred (Figure I.1). For these reasons, the first part of this book focuses on issues related to commercial biocontrol compounds. First, a description of the rules and regulations for the commercialization of biocontrol products is given by Robin et al. (Chapter 1). This chapter starts by giving definitions of the term “biocontrol” and also of other denominations used in the context of plant protection products (PPP) as required by the European regulation (e.g. “BioControl Agents”, “Active Substances”, “Biorationals”, etc.) even though the word “biocontrol” is not used as such. This chapter also discusses the problematic issues in these regulations regarding the use of biocontrol substances and the slow and long path to gaining the approval of biocontrol products in the PPP regulation. Limitations in the French and European regulations on so-called “biocontrol” products and the different possible suggestions to reform these regulations are also discussed.
Chapter 2 by Guibert et al. gives an overview of the various biocontrol products used in horticulture. Horticulture is a vast agronomic sector involving the cultivation of fruits, vegetables and ornamental plants. It is a major market for biocontrol products and targets both fresh and, in some cases, perishable products to improve shelf life. In the case of edible products, plant protection strategies should scrupulously avoid contamination by toxic substances and efforts should also be dedicated to preserving the gustative quality of the food in addition to conserving their nutritional value. In this sector, consumers are strongly concerned about the safety aspects of food products, as confirmed by the continuously increasing demand for organic farm produce. Although biocontrol has been integrated into horticultural practices for more than 40 years, the reduced or banned application of phytopharmaceutical products (e.g. glyphosate) has motivated cultivators to make fundamental changes and has also challenged many entrenched agricultural practices. The increase in the use of biocontrol methods and biostimulants, which is now under way, is largely driven by the greater awareness in society of the negative impact of pesticides, as described in Chapter 2. The authors describe the different trade-offs that must be considered in horticulture and the difficulties that farmers could encounter: the trade-off between plant growth and plant protection against disease as well as economic trade-offs linked to eco-innovations (increased costs, productivity gains, critical importance of certification and labeling on the marketplace, etc.). Further studies on the safety and environmental sustainability of biocontrol products are still needed before their deployment on the large scale as an alternative to PPP.
Chapter 3 by Ghosson et al. discusses this issue in detail. While biocontrol products are generally considered to be safer for the environment than chemical products, they are, by definition, biologically active products, and it is therefore necessary to analyze their environmental fate following their deployment. This aspect is related to regulatory rules that apply to biocontrol products, which are largely inspired by the existing rules for chemicals. However, a natural product is much more complex than its chemical alternative which is generally composed of a nearly pure molecule with formulants and adjuvant, and whose degradation products can be traced. Plant and microbial extracts contain thousands of metabolites, and it is almost impossible to predict the diversity of compounds produced by a living microorganism. As noticed by Ghosson et al. a way to circumvent these difficulties could be to apply “omics” or “meta-omics” strategies, notably genomics and metabolomics, to get a wider overview of a given product in the “omic” environment.
The second part of this book focuses on the development of biocontrol products based on active natural compounds obtained from plants (also known as botanicals) and microorganisms. Chapter 4 by Ntalli and Caboni presents a survey of the literature from the last 10 years on plant-based products whose ability to control root-knot nematodes has been assessed in vitro or in vivo, including in fields. Nematodes belonging to the Meloidogyne genus are major agricultural pests, and developing effective biocontrol strategies to combat root-knot nematodes is currently the subject of much research; significant advances have been made in recent times. Nevertheless, molecular targets within the nematode on which botanicals interact have only rarely been identified. In this context, Ntalli and Caboni describe few recent works which have investigated the mode of action of plant secondary metabolites on root-knot nematodes.
Agro-industrial wastes and by-products are inexpensive and abundant sources of bioactive molecules, notably those from the agroforestry sector or other industries that process plant materials. These products contain antioxidants, antimicrobials, insecticides and nematicides. With a special emphasis on nematicide activities, Chapter 5 by Andres and González Coloma presents the activities of agro-industrial wastes, which have been the subject of intense study in recent times. Such wastes include biochar produced from the pyrolysis of wood and other plant materials, by-products from the production of essential oils (hydrolates or hydrosols), and wastes from olive oil production. Through these examples, Andres and González Coloma suggest that agro-industrial wastes constitute an almost inexhaustible source of biopesticides, but more research is needed to improve their efficiency and reduce the potential phytotoxicity of these products.
We end the second part with Chapter 6 by Montesinos et al. which focuses on the development of novel plant disease protection strategies based on the use of antimicrobial peptides and defense elicitor peptides. Plants, animals and microorganisms synthesize a wide diversity of peptides that have antimicrobial properties, or are able to trigger the immune response of the plant. Several peptides have already shown their activity against plant pathogens in vitro or in planta under greenhouse conditions, but reports on their efficiency in fields are still scarce. Such peptides could be produced naturally or synthetically via heterologous expression systems implemented in plants or microorganisms. However, there are several challenges, including their facile synthesis in a cost-effective manner, improving their delivery/formulation and stability, all of which determine their efficiency in plant disease protection. A clear regulatory framework for their application as biocontrol products is also needed.
The third and last part of this book addresses the question of how biocontrol products may impact pathogen microbial development, notably by exploiting microbial signaling and microbe–microbe interactions. Biocontrol of plant pathogens via quorum quenching is discussed in Chapter 7 by Faure and Latour. Quorum quenching (QQ) refers to any of the mechanisms involved in the degradation of quorum-sensing (QS) molecules, whose concentrations increase with the proliferation of QS-emitting populations and thus act as signals. These signal molecules, when reaching a concentration threshold, can bind and activate transcriptional regulators to control the expression of QS-regulated genes, especially those involved in the biosynthesis of virulence factors, in several bacterial pathogens. Quorum quenchers can alter either of the two main steps in QS signaling pathways, namely the QS synthesis or the accumulation and interaction of QS signals with their regulators. Accordingly, there are two main types of quorum quenchers: QS inhibitors and QS-degrading enzymes having QQ activities and bacterial populations sharing this property that could be used as biocontrol agents. These agents target virulence factors of plant pathogens, but do not inhibit their population growth. QQ activity can be stimulated by using treatments that stimulate the proliferation of externally introduced or native QQ populations. Thus, QQ is an emerging novel biocontrol trait that is widely distributed in microbial soil communities. The efficiency of QQ treatments in combination with antibiosis approaches is currently under evaluation in field assays, and promising results are expected from these new biocontrol strategies.
Another strategy to counteract pathogenic development is by using bacteriophages. Bacteriophages (or phages) are an essential and often underestimated components of plant microbiota, notably in the rhizosphere. Due to their pathogenicity towards phytopathogenic bacteria and their specificity, phages are potentially attractive biocontrol agents. As described in Chapter 8 by Clavijo-Coppens et al. a number of phages targeting major phytopathogenic bacteria belonging to various genera (Acidovorax, Burkholderia, Erwinia, etc.) have been characterized and some of them have already been shown, at least in experiments under controlled conditions, to successfully control bacterial diseases on agronomically relevant plants. However, these encouraging results should be taken with caution in the face of technical challenges, which could hamper the use of phage preparations in agriculture. The cost of large-scale preparation of phage-based products has to be compatible with the overall cost of the commercial end-product in order to be acceptable to farmers, and progress also needs to be made in the formulation of phage-based products, notably regarding phage viability. An attractive approach, as for other biocontrol substances, could be coating seeds with a phage preparation, which could be an elegant way to protect plants while avoiding subsequent treatments in the field. Finally, the authors discuss the regulatory challenges faced by industrial actors who are willing to commercialize these new products. Despite the great potential of this strategy, there is little doubt that a deeper understanding of the role of phages in the plant ecosystem will be necessary to encourage the development of phage-based products.
Up to now, the development of biocontrol products has been mainly viewed as a replacement of chemicals by natural products exhibiting antimicrobial activities, hoping that these compounds are less harmful to the environment because of their natural origin. However, plant diseases can also be tackled by optimizing the functioning of the plant microbiota, which increasingly is being recognized as an essential component of plant health. Plant phyllosphere and rhizosphere host a myriad of microorganisms collectively designated as the microbiota. The microbiota is essential for plant life and fitness: it is a key contributor to plant nutrition and its resistance to biotic and abiotic stresses. In the last decade, metabarcoding investigations have pointed out the diversity of plant microbiota (rhizosphere, phyllosphere, spermosphere) in various plant species growing in contrasted environmental conditions. Recent results have shown that the composition of microbiota is in part, determined by the plant, notably with respect to the composition of plant exudates, and can be tuned to respond to new environmental conditions, and that certain microbial species can play a tremendous role in altering the biological function of the microbiota. In agricultural systems, chemical inputs which have been massively used for close to a century, has caused soil depletion and has had a dramatic impact on the diversity and functioning of plant microbiota. Thus, a major challenge of modern agriculture is to reconcile the highly reduced use of chemicals while maintaining high yields in agricultural environments that is today also strongly impacted by urbanization and climate change. One solution could come from the use of microbial formulations to help plants get nutrients and combat diseases while allowing the soil to recover its properties. However, the use of active microbial strains in agricultural systems has thus far not been optimized. Chapter 9 by Yu et al. addresses this essential issue and, on the basis of the latest progress made in this field, shows that new strategies could be proposed in the near future to optimize plant microbiota.
To conclude, these contributions together offer us a large panorama of the various strategies that are currently available or being developed to offer alternative environmentally safe products to combat plant diseases. They also point out the bottlenecks that hamper the introduction of these compounds into the market, notably the lengthy regulatory process that, at least in European countries, does not distinguish natural and chemical pesticides. However, the urgent need for alternative solutions to replace conventional products will undoubtedly support strong investment in this research field. Nevertheless, the road ahead is still long in facilitating regular use and improving the efficiency of biocontrol strategies. The transition from results acquired under greenhouse conditions to those acquired in fields over several consecutive years is still the most difficult step in the development of a biocontrol product. However, high magnitude and quality of research efforts on biocontrol strategies worldwide allows us to be optimistic about being able to provide farmers with novel nature-inspired biomimetics and efficient biocontrol solutions.
1Regulatory Aspects of Biocontrol
Diane ROBIN, Léa MERLET and Patrice MARCHAND
ITAB, France
Within the term “biocontrol”, only “biological control” thus macroorganisms (typical concept), “BioControl Agents” (BCAs) encompassing the three pillars outlined by Plant Protection Products Regulation EC 1107/2009 (namely microorganisms, semiochemicals and natural substances of plant, animal, mineral and microbial origin) and macroorganisms (fourth pillar) are considered. Macroorganisms are currently unregulated, except in France. For those considered as Plant Protection active substances, an approval pathway through EU Regulations follows general rules although some of these may be waived, depending on the pillar. In fact, 216 BioControl active substances are approved at the EU level, representing around 48% of total active substances (38% in 2011). Globally, and in a fairly stable way since 2011, around 50% are natural substances, 1/3 are microorganisms and 20% are semiochemicals. However, this significant progression, taking into account that 19 BioControl active substances were removed during the same period of time, is hiding the fact that many BioControl candidate substances are not being approved due to the inability to evaluate these substances (especially natural substances), which has left dozens of applicant substances unapproved.
1.1. Regulatory definition of biocontrol
1.1.1. Definitions of biocontrol
Biocontrol can be considered as including only biological control and macroorganisms, which follows the typical concept in the English-speaking world, or alternatively all the BioControl Agents (BCAs) encompassing the three pillars: microorganisms, semiochemicals and natural substances (of plant, animal, mineral and microbial origin) and occasionally including macroorganisms (fourth pillar), following the rather French and European concept set out by the International Biocontrol Manufacturers’ Association (IBMA) (Robin and Marchand 2019a). Sometimes this definition is extended to physical barriers (nets, monitoring traps, etc.), but this thinking has no specific regulations to date.
1.1.2. Applicable regulations
Biocontrol, within its BCA limits (BioControl Agents and Biocontrol products), has been under the control of the phytopharmaceutical regulation EC 1107/2009 (EC 2009b) at the European level, since 2011. Macroorganisms are not regulated in EU but when species are not endogenous, they are regulated in France (Robin and Marchand 2020).
1.1.2.1. Denominations – wording
Therefore, these products, and the substances which support them, even if they are not defined in such a way, are considered as “pesticides” sometimes with the alternate qualifiers of “biological pesticides”, “biopesticides”, “biorationals” or “BioControl agents” (BCA) in English.
1.1.2.2. Denominations – glossary
“Active substance” (a.s.) – substance from the three pillars regulated by Plant Protection Products Regulation EC 1107/2009 and listed in Regulation EC 540/2011.
“Product” – formulated approved active substance with market authorizations.
“Biocontrol product” – product with biocontrol active substance from the three pillars.
“Semiochemicals” – semiochemicals are defined by the European commission as substances or mixtures of substances emitted by plants, animals and other organisms that evoke a behavioral or physiological response in individuals of the same (= pheromones) or other (= allelochemicals) species. Natural-identical synthesized molecules are also included in this definition.
“Natural substances” – active substance of plant, mineral, animal or microbial origin, non-transformed or activated.
“Biological control” – generally dedicated to macroorganism uses.
“Biorationals” – generally considered as “natural substances” or of biological origin.
“Biocontrol” – may also be attributed to crop protection by living organisms: macroorganisms and microorganisms.
“BioControl Agents” or “BCAs” – commonly attributed to all biocontrol plant protection active substances.
1.2. Current issues and limitations
First, it has to be mentioned that the word “biocontrol” is absent in the Plant protection Products (PPP) regulation (EC 2009a). The notion of biocontrol is therefore external to the regulation that manages ¾ of the categories. Moreover, the word “biocontrol” is also absent in the Sustainable Use of pesticides Directive (SUD) (EC 2009b), although integrated pest management is mainstream, and biocontrol is one form of this concept. Consecutively, the concept of biocontrol or the biocontrol qualification of the substances and the corresponding product is from an external point of view; consequently, there is no official specific pathway or wavers during approval or renewal.
1.2.1. The 3 PPP pillars
During our study on their evolution, we showed at the ITAB institute that “biocontrol” active substances (a.s.) can belong to all parts from A to E (Robin and Marchand 2019b), and all types (active substance, low-risk, basic or candidate for substitution) of PPP regulation (Robin and Marchand 2021a). The notion of biocontrol applied to these substances is therefore diluted, and these substances diluted in EC Regulation 540/2011 and its sub-parts without distinction (Robin and Marchand 2021b) although the concept and the word “biocontrol” was not written in the PPP regulation. Many of these natural substances with non-biocidal properties and modes of action (MoA) are of very low toxicological concern and therefore do not have maximum residue limits (MRLs) (Charon et al. 2019). However, even if some would want to generalize that belief, their toxicity is not always trivial.
1.2.2. Fourth pillar
Global biocontrol includes macroorganisms, which fall under neither PPP regulation nor any specific regulation at the European level. At the national level, only France regulates transfers of non-native macroorganisms from mainland France to overseas territories, including Corsica (Journal Officiel “Lois et Décrets” (JORF) 2022), and vice versa (Robin and Marchand 2020). It aims to avoid the potential problems of the propagation of non-native macroorganisms, which could become invasive species outside their indigenous territory. Use is granted when this risk is guaranteed to be null (inadequate adaptation to the European climate, for example), and global warming could affect certain authorizations in the long term. In addition, French regulations may be partially or completely taken up by Europe in the long term. This path is indeed currently followed by the EU with recent regulatory incentives (EU 2021a) paving the way for the regulation of macroorganisms.
1.2.3. Limits with crop protection in Organic Agriculture
First of all, the four pillars of biocontrol are acceptable in Organic Farming ruled by Regulation EU 2018/848 (EU 2018b), the question of GMOs or GMO-produced substances being regulated in a similar way to the previous regulation (EU 2008b). The current global restriction avoiding the use of herbicides (a de facto total ban) implies that weeds are managed mainly by physical methods (mechanically, thermically or electrically). The global question of crop protection is managed primarily by protection from natural predators, the choice of species and varieties, crop rotation, cultivation techniques, mechanical methods and physical and thermal processes. Questions on new herbicide techniques (electricity) are currently being assessed. The question of “transformed” natural substances is also at the heart of debates. Three out of four pillars are automatically authorized in Organic Production: macroorganisms, microorganisms and chemical mediators. The authorizations of natural substances (of plant, animal, mineral and microbial origin) are managed on an ad hoc and individual basis for each active substance and are subject to voluntary inclusion files in Annex I (protection of crops and foodstuffs and stored products by extension), deposited at the national level and managed by the DGAgri through EGTOP PPP examination mandates (EGTOP 2017). Most of these natural biocontrol substances are thus accepted (Marchand 2017), except herbicides and substances that regulate positive (auxins) or negative (herbicides) growth. Annex I is under deep discussion, with the creation of sub-parts that did not previously exist, such as natural substances obtained from microorganisms (currently spinosad, cerevisane, ABE IT 56), specific parts for low-risk substances (EU 2017b; Robin and Marchand 2021b, 2021c) and basic substances (Marchand 2015, 2017; Robin and Marchand 2019a; Marchand et al. 2021). In conclusion, almost all biocontrol substances and products of the four pillars are accepted in Organic Agriculture (EGTOP 2021).
1.2.4. Limits of biocontrol: contentious substances!
Natural substances, including some chemical mediators, are not free from toxicity, and many examples show this, such as rotenone. Aside the natural substances historically used for lethal purposes (Bacalexi and Katouzian-Safadi 2018), some natural substances have been withdrawn from approval (e.g. crude tall oil) (EU 2017a), or never got approved in PPP Regulation (e.g. rotenone, nicotine) (EC 2008a). Direct comparisons show that the differences between “synthetic” and “natural” substances are not as sharp and the conclusions are sometimes not as dichotomous as society may think (Smith and Perfetti 2020). A similar acceptance problem may be encountered with copper compounds that are candidates for the substitution (as for emamectin, for example (EU 2020; Robin and Marchand 2021b)).
1.3. A mixed evolution
Biocontrol substances are increasing in number and percentage, relative to the total number of active substances approved in PPP regulation, mainly through the reduction of synthetic chemical substances (for the percentage) and subdivision of the lists of microorganisms by strain as an individual active substance (for the amounts). Of course, newly approved BCAs also account for the increase in both indicators (amount and percentage). In addition, the delimitation between biocontrol and synthetic substances is unclear, because certain synthetic chemicals can be used in biocontrol, in particular, in the “kill” part of “attract and kill” traps, which are also approved in organic farming plant protection (EU 2021b), although some member states asked to remove them from Annex I (Marchand 2019).
Thus, the number of biocontrol substances rose from 147 (38%) initially in 2011 to 216, representing 48% of all active substances, in 2022. The increase is very significant in number (+ 47%) but still low in overall percentage. The date by which biocontrol substances will represent 50% of all active substances, initially predicted to be 2025 (in 2018), is currently scheduled for 2022 – which is today. It is important to reason in terms of the active substance because a single substance can give rise to many different products, usages and even functions. As such, the visible increase in the number of biocontrol products on the French List only comes from the multiplication of products, often for redundant uses, based on just a few substances. Sometimes, even new active substances only have redundant uses, like ferric pyrophosphate and the already-approved ferric phosphate (Robin and Marchand 2021b).
In spite of this encouraging growth, the arrival of new active biocontrol substances and solutions approved under the PPP regulation is extremely slow, even if the annual percentage of new biocontrol substances in relation to the total annual new active substances is increasing (and was even 100% in both 2020 and 2021). The approval of biocontrol active substances submitted by petitioners is far from guaranteed, including for candidates with market authorizations in other countries (USA, Canada) ending up unapproved in Europe after the usual obstacle course of active substance approval (Vekemans and Marchand 2020).
Despite the regulatory changes since the implementation of Regulation 1107/2009 in 2011 (EC 2009a) compared to previous Directive 91/414/EC, progress is still slow. Even the renewal of these substances is not assured despite the interest they represent; many previously approved biocontrol substances have been lost, not supported for renewal or abandoned by petitioners for varying causes: too few uses and/or not enough specificity (estimated or real) leading to low sales volumes. In four years, 6% of the 80 substances lost were biocontrol substances. This phenomenon particularly affects substances that are accessible by other means than the phytosanitary protection market (pepper powder, ammonium phosphate, ammonium acetate). Reapproval of these active substances into basic substances is still possible. Basic substances (Marchand 2015) currently account for 11% of biocontrol substances (24 a.s. out of 216); they do not require market authorization and therefore are not protected. Nevertheless, a significant number of new microorganisms, 15 substances as of January 2022, are in the process of being approved, many with low-risk status.
1.3.1. Struggling bases
With regulatory considerations of the “new” PPP regulation arriving in 2011, low-risk substance rapidly appeared to be poorly defined since modifications occurred in 2018 (EU 2017b, 2018a) and new modifications for microorganisms are ongoing, hopefully for the better.
1.3.2. Achieved progress
A lightening of constraints has occurred in response to the difficulties encountered during the approval and renewal of microorganisms. Indeed, microorganisms as biocontrol active substances could legitimately claim the status of low-risk active substances. Previously, it took years of existence of the PPP regulation to modify the criteria for low-risk substances so that microorganisms could more easily access this status, whereas the previous criteria (DT50 less than 60 days) of point 5 of Appendix II strongly prevented microorganisms from achieving this status (EU 2017b). Appendix II of Regulation 1107/2009 was therefore seriously modified.
The Commission (DGSanté) thus organized a working group in 2017 to refine the criteria previously defined for low-risk substances. This work was subsequently published, updating Annex II, point 5, with Regulation (EC) No. 1107/2009, distinguishing between microorganisms and natural substances. This work also made it possible to establish a list of potential low-risk substances from already approved active substances (EU 2018a). As no direct transfer or grant from the defined list was recognized at that time, the transfer operation to low-risk status was deemed finalized during the individual renewal of the active substance. It is therefore slow and haphazard since one of the potential substances, garlic extract, has not been renewed in a low-risk substance (Robin and Marchand 2021c).
This statute must ensure marketing authorizations by law within 120 days of approval, but in fact, the deadlines are much longer (up to 754 days on average in Germany). In addition, the benefits granted to these low-risk substances depend on Article 22 (EU 2017c). Ongoing progress in the modification of microorganism evaluation, concretely “amending Annex II to Regulation (EC) No. 1107/2009 as regards specific criteria for the approval of active substances that are microorganisms” to consider all low-risk criteria applying to viruses which are non-virulent variants of plant pathogens, rather than to baculovirus only.
1.3.3. Regulatory relief for semiochemicals
1.3.3.1. Features
Semiochemicals are one of the four types of biocontrol and are considered active substances, thus falling under the 1107/2009 regulation (EC 2009a) when it comes to communal approbation.
These substances are emitted at very low levels in the environment by many different organisms. They fulfill a wide variety of roles and communications within and between species. It results that humans and other non-target species, as well as the environment, are constantly exposed to very low levels of various semiochemicals emitted by the different organisms present in the environment (insects, fragrant plants, etc.). As such, their mode of action is non-lethal and very specific to the receptor system of the receiving organism. These receptor systems are tuned to natural emission rates, which means that an efficient rate for plant protection use must be of the same magnitude. Indeed, a rate that is too high can modify or negate the expected effect. Because of these properties, it is expected that semiochemicals used as plant protection product pose a low risk to human health and the environment.
In the context of plant protection, different semiochemical communications have been exploited. The most common use is mating disruption, where a female sex pheromone is heavily released into the environment, which disrupts male ability to find a female, thus reducing mating and the next generation. Attractant pheromones can be used in “attract and kill” systems, in which an attractant is used to lure insects into a trap where they are killed by different means (insecticide, drowning, glue, etc.), or in “mass trapping” systems that use male emitted pheromones to attract and trap females, thus reducing egg-laying and subsequent larvae damage. Finally, repellents can be used to deter insects or inhibit their behaviors (feeding, ovipositing, etc.), although this last category of plant protection product has not yet been properly developed.
Guidelines. Straight Chain Lepidopteran Pheromones (SCLPs) representing a large part of the semiochemicals, a general “Guidance Document on the assessment of new substances falling into the group of Straight Chain Lepidopteran Pheromones (SCLPs) included in Annex I of Council Directive 91/414/EEC”, was published in 2008 (DGSanté 2008). To further facilitate the application and approbation of semichemical substances, and to integrate the knowledge gained since 2003, a new “Guidance Document on semiochemicals active substance and plant protection products” was published in May 2016 (SANTE/12815/2014 rev. 5.2) (DGSanté 2016a) and later validated by OECD (OECD 2018) accompanied by efficacy evaluation guidance (EOPP 2019).
1.3.3.2. Natural exposure level and reduced risk evaluation
The new guidance document introduces the notion of natural exposure level, defined as “the level of exposure that might occur in the environment by high population of emitting organisms thus expected to be experienced by humans and other non-target organisms”.
This notion is a key point in semiochemicals risk assessment. Indeed, if the applicant shows the use of their product results in environmental exposure by the same route and of lower or equivalent rate to the natural exposure level, then the risk assessment is concluded. In this ideal situation, only the identity, physical and chemical properties and information about the formulated product are needed. The sections about mammalian toxicology, residues and MRL, effects on non-target species and environmental fate and behavior do not have to be completed. The Guidance provides two different formulas to calculate the natural exposure level and exposure rate resulting from use as PPP.
However, if the exposure resulting from use as PPP is significantly higher than the natural exposure level then the final concentration derived from using the product should be calculated using a proposed model. The risk assessment continues, and all sections must be completed. Similarly, if oral and/or contact exposure is possible (e.g. spray, granules, treated seeds), then the full risk assessment to these routes is always needed.
1.3.3.3. Natural exposure level and reduced risk evaluation
Taking into account semiochemical specificity, the guidance document provides some advice on how to integrate the specific features of semiochemicals into the required dossier data.
As much detail as possible must be given about the biology and communication mechanisms between the organisms involved, about the specificity of that interaction and about the mode of action of the product in terms of how it modifies the behavior of the target organism. All this information on the biology of the interaction must be provided to justify the risk assessment strategy.
The use of semiochemicals as PPP relies on the release of low rates of volatile product for a long time, over different patterns, to maintain levels of exposure both tuned to the target species receptor system, and of the same magnitude as natural exposure level. The exposure rate is heavily determined by the characteristics of the dispenser or type of application, and as such, they must be thoroughly described. The guidance document provides details and examples in its appendix on the different types of existing application techniques. Moreover, information on the density, position, periods and frequencies of use of the dispensers must be provided, as well as factors affecting how the product should be used (weather, landscape, etc.).
All dossiers require demonstrating that the PPP is sufficiently effective and does not have unacceptable effects on the plant or plant products. The document notes that deviation from standard requirements and guidance may be required for some parts of the biological assessment dossier to account for the specific properties of semiochemicals. It is also noted that efficacy field trials for semiochemicals may be difficult to replicate and on a large scale. It is accepted that semiochemicals used as PPP may provide more or less control and have a more variable performance compared to a conventional product. Any reduced efficiency in terms of pest elimination will not in itself be a cause for refusal and other measures of efficacy will be considered, such as offering an alternative mode of action relevant to resistance management, reduced residues and compatibility with specific growing systems. Overall, the applicant must demonstrate a statistically significant improvement of an appropriate measure of either pest control, crop damage or crop yield that would be beneficial from an agronomic perspective.
1.3.3.4. Specific case of attractants within traps
1.3.3.4.1. EU implementation
In the Guidance document, it is specified that “semiochemicals are not considered active substances, when they are used only to attract arthropods” with the purpose of monitoring or within traps where they are subsequently killed. This means that when semiochemicals are attractant of arthropods used in traps, they do not fall under the 1107/2009 PPP regulation and are thus exempt from registration.
1.3.3.4.2. French implementation
On September 22, 2020, the French authority published a technical instruction (DGAL/SDQSPV/2020-581) reprising this notion. It clarifies those traps used for monitoring or “mass trapping” that rely on semiochemicals as attractant do not need market authorization if the trap is exempt of insecticides. The same exemption from market authorization applies if the attractant within the trap is a food product. On the other hand, if insects attracted to the trap are killed by an insecticide active substance, both the communal approval of the insecticide and the market authorization of the trap are required. This last technique, which avoids contact with chemical insecticides, is relatively safe and is also authorized in Organic Production (Marchand 2019).
1.3.4. Regulatory relief for microorganisms
1.3.4.1. Features
Microorganisms are one of the four types of biocontrol and are considered active substances, thus falling under the 1107/2009 regulation (EC 2009a) when it comes to communal approbation.
General considerations are described by “Guidance Document for applicants on preparing dossiers for the approval of a microbial active substance” published in March 2016 (SANTE/12545/2014–rev. 3) (DGSanté 2016b), but specific points may be found in “Guidance Document on the assessment of new isolates of baculovirus species already included in Annex I of Council Directive 91/414/EEC” published in 2008 (SANCO/0253/2008 rev. 2) (DGSanté 2008) and “Guideline developed within the Standing Committee on the Food Chain and Animal Health on the taxonomic level of microorganisms to be included in Annex I to Directive 91/414/EEC” published in 2005 (SANCO/10754/2005 rev.5) (DGSanté 2005).
1.3.4.2. Evolution
Considering the specificity of microorganisms, recent documents were generated by the Commission in 2020 (DGSanté 2020a, 2020b) in order to consider and manage metabolite production (SANTE/2020/12258) and antimicrobial resistance (SANTE/2020/12260) especially during low-risk status considerations.
1.3.5. Regulatory relief for natural substances
Natural substances are one of the four types of biocontrol and are considered active substances, thus falling under the 1107/2009 regulation (EC 2009b) when it comes to communal approbation. Botanicals, natural substances from plant origin, are the only one of the natural substances considered by approval guidance. The possible explanation is that only few natural substances of animal/microbial or mineral origin are candidates.
General considerations for plant extracts are described by “Guidance Document on botanical active substances used in plant protection products”, published in March 2014 (SANTE/11470/2012 rev. 8) (DGSanté 2014).
1.4. Necessary evolutions
1.4.1. At the EU level
An effective first step towards a better consideration of biocontrol would be at least to include a clear definition of “biocontrol” in plant protection regulation (EC 2009), or even to create a specific category within the regulation to ease understanding. Although the approbation process and dossier size are reduced for biocontrol substances and relatively easier to compile compared to synthetic substances, this progress in promoting approbation of biocontrol substances only favors some of the four pillars. Thus, among recent applications, most are variations of microorganisms with similar behaviors: eight Bacillus sp. and six Trichoderma sp. Furthermore, the SUD (EC 2009b) should be an effective lever for the amplification of biocontrol, which it is not (Robin and Marchand 2019c, 2022; Vekemans and Marchand 2020, 2022).
1.4.2. At the national level (France)
All low-risk substances and almost all basic substances are biocontrol substances. The inscription of substances on the list of “potentially” low-risk substances could also be a positive sign. In contrast, reducing requirements does not seem to be on the agenda (Smith and Perfetti 2020) apart from classification by families, for example, Bacillus
