Introduction

Promoting 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.1 Necessary 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...