Evolution of the biocontrol active substances in the framework of the European Pesticide Regulation (EC) No. 1107/2009

Trunk Injection Delivery of Biocontrol Strains of Trichoderma spp. Effectively Suppresses Nut Rot by Gnomoniopsis castaneae in Chestnut (Castanea sativa Mill.)

Gnomoniopsis castaneae is responsible for brown or chalky nut rot in sweet chestnut (Castanea sativa), causing heavy reductions in nut production. Controlling it is challenging, due to its inconspicuous infections, erratic colonization of host tissues and endophytic lifestyle. Fungicides are not applicable because they are prohibited in chestnut forests and strongly discouraged in fruit chestnut groves. Trichoderma species are safe and wide-spectrum biocontrol agents (BCAs), with a variety of beneficial effects in plant protection. This study tested selected strains of T. viride, T. harzianum and T. atroviride for their ability to suppress G. castaneae. Field experiments were conducted in four chestnut groves (two test plots plus two controls) at two sites with a different microclimate. As the size of the trees were a major drawback for uniform and effective treatments, the Trichoderma strains were delivered directly by trunk injection, using the BITE® (Blade for Infusion in TrEes) endotherapic tool. The BCA application, repeated twice in two subsequent years, significantly reduced nut rot incidence, with a more marked, presumably cumulative, effect in the second year. Our data showed the tested Trichoderma strains retain great potential for the biological control of G. castaneae in chestnut groves. The exploitation of Trichoderma spp. as biopesticides is a novelty in the forestry sector and proves the benefits of these microbes in plant disease protection.

Natural Products Targeting the Fungal Unfolded Protein Response as an Alternative Crop Protection Strategy

Discovering new solutions for crop protection is a major challenge for the next decades as a result of the ecotoxicological impact of classical fungicides, the emergence of fungicide resistances, and the consequence of climate change on pathogen distribution. Previous work on fungal mutants deficient in the unfolded protein response (UPR) supported that targeting this pathway is a promising plant disease control strategy. In particular, we showed that the UPR is involved in fungal virulence by altering cell protection against host defense compounds, such as phytoalexins and phytoanticipins. In this study, we evaluated natural products targeting fungal IRE1 protein (UPR effector) and consequently increasing fungal susceptibility to plant defenses. Developing an in vitro cell-based screening assay allowed for the identification of seven potential IRE1 inhibitors with a focus on polyhydroxylated prenylated xanthones. Inhibition of hac1 mRNA splicing, which is mediated by IRE1, was then validated for the most active compound, namely, γ-mangostin 3. To study the mode of interaction between the binding site of IRE1 and active xanthones, molecular docking was also undertaken, revealing similar and novel interactions between the known inhibitor and the binding site. Eventually, active xanthones applied at subtoxic doses induced a significant reduction in necrosis size for leaves of Brassica oleracea inoculated with Alternaria brassicicola and Botrytis cinerea.

Making the best of research investment in pathogens control through biocontrol. How is research correlated with agricultural microbial biological control product availability?

While using microbial biological control products (MBCPs) to limit pathogens is one of the alternatives to the ecologically unsustainable use of synthetic pesticides that received attention, the last 2 decades have not brought the foreseen leap in developing systematic alternatives based on low-risk plant protection products (PPPs) across the globe. To explain this limited progress, we map the evolution of research on the most successful microbial biological control agents (MBCAs) worldwide. We also map the financing structure in the top funding countries and the European Union (EU) to discern the relevant trends. Available data for the European Union Member States allowed us to discover a country-level and EU-level correlation between strain-level research and biocontrol products' approval based on those strains.

Evolution of plant protection active substances in Europe: the disappearance of chemicals in favour of biocontrol agents

With the entry into force of Regulation EC 1107/2009 and the important cut-off of a number of existing active substances from before 2011, which was processed from 342 in Annex I of Directive 91/414/EEC to 298, all these active substances are listed in Part A of Regulation EU 540/2011. Here, we have conducted a survey of all active substances since concerning their regulatory characteristics and their agricultural uses. Between 2011 and 2018, a global increase in active substances was observed with up to 502 approved, but since then an inexorable decline in the number active substances has occurred, despite numerous biocontrol agents (BCAs) being approved and only few chemicals. The newly approved active substances were then listed in Parts B, C, D and E, while renewed substances moved to Parts B to E. The impact of these changes was studied in relation to the availability of these substances and the corresponding global modifications in terms of employment, functions, uses, crops, and maximum residue limits. There has been a net loss of 53 active substances since 2018, notwithstanding 30 approvals, equates to a real loss of 95 active substances in the last 4 years and 118 since 2011. The main reduction of active substances is not only due to a falling-off of chemicals (95) but also a significant decay of BCA (19) impacting crop protection with an important reduction of the herbicides and a small increase of fungicides with an high replacement rate, with all crops being impacted, while the residue situation has greatly improved.

A meta-analysis of ecotoxicological models used for plant protection product risk assessment before their placing on the market

Before their placing on the market, the safety of plant protection products (PPP) towards both human and animal health, and the environment has to be assessed using experimental and modelling approaches. Models are crucial tools for PPP risk assessment and some even help to avoid animal testing. This review investigated the use of modelling approaches in the ecotoxicology section of PPP active substance assessment reports prepared by the authorities and opened to consultation from 2011 to 2021 in the European Union. Seven categories of models (Structure-Activity, ToxicoKinetic, ToxicoKinetic-ToxicoDynamic, Species Sensitivity Distribution, population, community, and mixture) were searched for into the reports of 317 active substances. At least one model category was found for 44 % of the investigated active substances. The most detected models were Species Sensitivity Distribution, Structure-Activity and ToxicoKinetic for 27, 21 and 15 % of the active substances, respectively. The use of modelling was of particular importance for conventional active substances such as sulfonylurea or carbamates contrary to microorganisms and plant derived substances. This review also highlighted a strong imbalance in model usage among the biological groups considered in the European Regulation (EC) No 1107/2009. For example, models were more often used for aquatic than for terrestrial organisms (e.g., birds, mammals). Finally, a gap between the set of models used in reports and those existing in the literature was observed highlighting the need for the implementation of more sophisticated models into PPP regulation.

Bacteria as Biological Control Agents of Plant Diseases

Biological control is an effective and sustainable alternative or complement to conventional pesticides for fungal and bacterial plant disease management. Some of the most intensively studied biological control agents are bacteria that can use multiple mechanisms implicated in the limitation of plant disease development, and several bacterial-based products have been already registered and marketed as biopesticides. However, efforts are still required to increase the commercially available microbial biopesticides. The inconsistency in the performance of bacterial biocontrol agents in the biological control has limited their extensive use in commercial agriculture. Pathosystem factors and environmental conditions have been shown to be key factors involved in the final levels of disease control achieved by bacteria. Several biotic and abiotic factors can influence the performance of the biocontrol agents, affecting their mechanisms of action or the multitrophic interaction between the plant, the pathogen, and the bacteria. This review shows some relevant examples of known bacterial biocontrol agents, with especial emphasis on research carried out by Spanish groups. In addition, the importance of the screening process and of the key steps in the development of bacterial biocontrol agents is highlighted. Besides, some improvement approaches and future trends are considered.

Basic Substances, a Sustainable Tool to Complement and Eventually Replace Synthetic Pesticides in the Management of Pre and Postharvest Diseases: Reviewed Instructions for Users

Synthetic pesticides are widely used to protect crops from pathogens and pests, especially for fruits and vegetables, and this may lead to the presence of residues on fresh produce. Improving the sustainability of agriculture and, at the same time, reducing the adverse effects of synthetic pesticides on human health requires effective alternatives that improve the productivity while maintaining the food quality and safety. Moreover, retailers increasingly request fresh produce with the amounts of pesticides largely below the official maximum residue levels. Basic substances are relatively novel compounds that can be used in plant protection without neurotoxic or immune-toxic effects and are still poorly known by phytosanitary consultants (plant doctors), researchers, growers, consumers, and decision makers. The focus of this review is to provide updated information about 24 basic substances currently approved in the EU and to summarize in a single document their properties and instructions for users. Most of these substances have a fungicidal activity (calcium hydroxide, chitosan, chitosan hydrochloride, Equisetum arvense L., hydrogen peroxide, lecithins, cow milk, mustard seed powder, Salix spp., sunflower oil, sodium chloride, sodium hydrogen carbonate, Urtica spp., vinegar, and whey). Considering the increasing requests from consumers of fruits and vegetables for high quality with no or a reduced amount of pesticide residues, basic substances can complement and, at times, replace the application of synthetic pesticides with benefits for users and for consumers. Large-scale trials are important to design the best dosage and strategies for the application of basic substances against pathogens and pests in different growing environments and contexts.

Quantitative High-Throughput Screening Methods Designed for Identification of Bacterial Biocontrol Strains with Antifungal Properties

Large screens of bacterial strain collections to identify potential biocontrol agents often are time-consuming and costly and fail to provide quantitative results. In this study, we present two quantitative and high-throughput methods to assess the inhibitory capacity of bacterial biocontrol candidates against fungal phytopathogens. One method measures the inhibitory effect of bacterial culture supernatant components on the fungal growth, while the other accounts for direct interaction between growing bacteria and the fungus by cocultivating the two organisms. The antagonistic supernatant method quantifies the culture components' antifungal activity by calculating the cumulative impact of supernatant addition relative to the growth of a nontreated fungal control, while the antagonistic cocultivation method identifies the minimal bacterial cell concentration required to inhibit fungal growth by coinoculating fungal spores with bacterial culture dilution series. Thereby, both methods provide quantitative measures of biocontrol efficiency and allow prominent fungal inhibitors to be distinguished from less effective strains. The combination of the two methods sheds light on the types of inhibition mechanisms and provides the basis for further mode-of-action studies. We demonstrate the efficacy of the methods using Bacillus spp. with different levels of antifungal activities as model antagonists and quantify their inhibitory potencies against classic plant pathogens. IMPORTANCE Fungal phytopathogens are responsible for tremendous agricultural losses on an annual basis. While microbial biocontrol agents represent a promising solution to the problem, there is a growing need for high-throughput methods to evaluate and quantify inhibitory properties of new potential biocontrol agents for agricultural application. In this study, we present two high-throughput and quantitative fungal inhibition methods that are suitable for commercial biocontrol screening.

EU microbial pest control: A revolution in waiting

Recent evaluations of the microbial biological control sector indicate that implementing microbial control of pests is still slow in the EU. The top causal factors are the lengthy, expensive, and cumbersome two-stage procedure for approval of biological agents as active substances at the EU level and authorization of formulated products at the national level, limited funding, lack of EU level integrated approaches, and slow implementation of integrated pest management. This article contributes to a better understanding of the factors that limit microbial control of pests in EU agriculture by providing the first evaluation of the evolution of microbial biological control agent (MBCA) EU-level approval combined with that of microbial biological control product (MBCP) national-level authorization, discusses recent trends in research and offers some policy recommendations. By 2020, the EU had caught up with the USA regarding research output, approved MBCAs, and MBCA approval procedures (first stage). Despite improvements from 2014 to 2019, the number of authorized MBCPs (second stage) has progressed slowly and unevenly across the EU. Significant progress is concentrated in countries with more extensive agricultural land and higher research intensity. The EU's focus on promoting more sustainable agriculture by increasing the availability of low-risk pesticides of biological origin as alternatives to conventional chemical pesticides has gained traction in recent years. Nevertheless, more efforts to improve the capacity and expertise of laggard EU Member States to contribute to the approval of MBCA, authorization of MBCP, and stimulating market availability are needed. Furthermore, we recommend introducing more concrete measures to promote the adoption of the microbial control of pests in the National Action Plans for the sustainable use of pesticides. © 2021 Society of Chemical Industry.

Critical Review: Role of Inorganic Nanoparticle Properties on Their Foliar Uptake and in Planta Translocation

There is increasing pressure on global agricultural systems due to higher food demand, climate change, and environmental concerns. The design of nanostructures is proposed as one of the economically viable technological solutions that can make agrochemical use (fertilizers and pesticides) more efficient through reduced runoff, increased foliar uptake and bioavailability, and decreased environmental impacts. However, gaps in knowledge about the transport of nanoparticles across the leaf surface and their behavior in planta limit the rational design of nanoparticles for foliar delivery with controlled fate and limited risk. Here, the current literature on nano-objects deposited on leaves is reviewed. The different possible foliar routes of uptake (stomata, cuticle, trichomes, hydathodes, necrotic spots) are discussed, along with the paths of translocation, via the phloem, from the leaf to the end sinks (mature and developing tissues, roots, rhizosphere). This review details the interplays between morphological constraints, environmental stimuli, and physical-chemical properties of nanoparticles influencing their fate, transformation, and transport after foliar deposition. A metadata analysis from the existing literature highlighted that plant used for testing nanoparticle fate are most often dicotyledon plants (75%), while monocotyledons (as cereals) are less considered. Correlations on parameters calculated from the literature indicated that nanoparticle dose, size, zeta potential, and affinity to organic phases correlated with leaf-to-sink translocation, demonstrating that targeting nanoparticles to specific plant compartments by design should be achievable. Correlations also showed that time and plant growth seemed to be drivers for in planta mobility, parameters that are largely overlooked in the literature. This review thus highlights the material design opportunities and the knowledge gaps for targeted, stimuli driven deliveries of safe nanomaterials for agriculture.

Biological Control of Plant Diseases: An Evolutionary and Eco-Economic Consideration

Biological control is considered as a promising alternative to pesticide and plant resistance to manage plant diseases, but a better understanding of the interaction of its natural and societal functions is necessary for its endorsement. The introduction of biological control agents (BCAs) alters the interaction among plants, pathogens, and environments, leading to biological and physical cascades that influence pathogen fitness, plant health, and ecological function. These interrelationships generate a landscape of tradeoffs among natural and social functions of biological control, and a comprehensive evaluation of its benefits and costs across social and farmer perspectives is required to ensure the sustainable development and deployment of the approach. Consequently, there should be a shift of disease control philosophy from a single concept that only concerns crop productivity to a multifaceted concept concerning crop productivity, ecological function, social acceptability, and economical accessibility. To achieve these goals, attempts should make to develop “green” BCAs used dynamically and synthetically with other disease control approaches in an integrated disease management scheme, and evolutionary biologists should play an increasing role in formulating the strategies. Governments and the public should also play a role in the development and implementation of biological control strategies supporting positive externality.

Volatile Organic Compounds (VOCs) Produced by Gluconobacter cerinus and Hanseniaspora osmophila Displaying Control Effect against Table Grape-Rot Pathogens

Table grapes (Vitis vinifera) are affected by botrytis bunch rot and summer bunch rot, the latter a complex disease caused by Botrytis cinerea, Aspergillus spp., Penicillium expansum and Rhizopus stolonifer. To search for biocontrol alternatives, a new bioproduct composed of Gluconobacter cerinus and Hanseniaspora osmophila, a consortium called PUCV-VBL, was developed for the control of fungal rots in table grapes. Since this consortium presents new biocontrol species, the effect of their VOCs (volatile organic compounds) was evaluated under in vitro and in vivo conditions. The VOCs produced by the PUCV-VBL consortium showed the highest mycelial inhibition against Botrytis cinerea (86%). Furthermore, H. osmophila was able to inhibit sporulation of A. tubingensis and P. expansum. VOCs' effect in vivo was evaluated using berries from Red Globe, Thompson Seedless and Crimson Seedless grapes cultivars, demonstrating a mycelial inhibition by VOCs greater than 70% for all evaluated fungal species. The VOC identification of the PUCV-VBL consortium was analyzed by solid-phase microextraction coupled to gas chromatography-mass spectrometry (SPME-GCMS). A total 26 compounds were identified, including 1-butanol 3-methyl, propanoic acid ethyl ester, ethyl acetate, phenylethyl alcohol, isobutyl acetate and hexanoic acid ethyl ester. Our results show that VOCs are an important mode of action of the PUCV-VBL biological consortium.

High-Pressure-Sprayed Double Stranded RNA Does Not Induce RNA Interference of a Reporter Gene

In plants, RNA interference (RNAi) is an effective defense mechanism against pathogens and pests. RNAi mainly involves the micro RNA and the small interfering RNA (siRNA) pathways. The latter pathway is generally based on the processing of long double stranded RNAs (dsRNA) into siRNAs by DICER-LIKE endonucleases (DCLs). SiRNAs are loaded onto ARGONAUTE proteins to constitute the RNA-induced silencing complex (RISC). Natural dsRNAs derive from transcription of inverted repeats or of specific RNA molecules that are transcribed by RNA-directed RNA polymerase 6 (RDR6). Moreover, replication of infecting viruses/viroids results in the production of dsRNA intermediates that can serve as substrates for DCLs. The high effectiveness of RNAi both locally and systemically implicated that plants could become resistant to pathogens, including viruses, through artificial activation of RNAi by topical exogenous application of dsRNA. The most preferable procedure to exploit RNAi would be to simply spray naked dsRNAs onto mature plants that are specific for the attacking pathogens serving as a substitute for pesticides applications. However, the plant cell wall is a difficult barrier to overcome and only few reports claim that topical application of naked dsRNA triggers RNAi in plants. Using a transgenic Nicotiana benthamiana line, we found that high-pressure-sprayed naked dsRNA did not induce silencing of a green fluorescence protein (GFP) reporter gene. Small RNA sequencing (sRNA-seq) of the samples from dsRNA sprayed leaves revealed that the dsRNA was, if at all, not efficiently processed into siRNAs indicating that the dsRNA was insufficiently taken up by plant cells.

The fate of biocontrol agents under the European phytopharmaceutical regulation: how this regulation hinders the approval of botanicals as new active substances

The use of biocontrol agents (BCAs) is growing across the world and in Europe in particular, where novel ways of farming are highly encouraged and implemented. However, although the social pressure is high to increase the number of BCAs in use within the EU, the European plant protection products (PPP) regulation (EC) N° 1107/2009 does not define clearly what BCAs are. Therefore, problems and drawbacks are observed throughout the whole authorisation process. Consequently, this situation impedes drastically the rapid implementation of botanical BCAs and their subsequent use in the field. Previous studies described in detail the fate of BCAs and the current administrative process that leads to their approval. Drawbacks are described for GMOs but surprisingly scarcely for pesticides. Therefore, the present study pinpoints the drawbacks of the approval process of botanical BCAs. To achieve this goal, a comparative study of 5 substances (4 of plant origin and 1 chemical) was performed. This study clearly reveals the present weaknesses and loopholes in the European PPP regulation process. The results of the present study may be useful to initiate and promote a major change in the evaluation and the regulation process of BCAs. This should allow designing a novel and innovative framework enabling the development of future plant protection products according to the sustainable use of pesticides, described in the corresponding (EC) Directive N° 128/2009 (SUD). This work targets farmers, policy makers, NGOs and scientists interested in issues related to this topic.

Preparation of Matrinic/Oxymatrinic Amide Derivatives as Insecticidal/Acaricidal Agents and Study on the Mechanisms of Action against Tetranychus cinnabarinus

In continuation of our program to develop natural-product-based pesticidal candidates, matrinic/oxymatrinic amides were obtained through structural optimization of matrine. N'-(4-Fluoro)phenyl-N-(4-bromo)phenylsulfonyloxymatrinic amide (IIm) showed potent insecticidal activity against Mythimna separata. N-(Un)substituted phenylsulfonylmatrinic acids (3a-c) exhibited promising acaricidal activity against Tetranychus cinnabarinus. By qRT-PCR analysis of nAChR subunits and AChE genes and determination of AChE activity of (un)treated T. cinnabarinus, it suggested that the open lactam ring of matrine and carboxyl group and (4-methyl)phenylsulfonyl of N-(4-methyl)phenylsulfonylmatrinic acid (3b) were necessary for action with α2, α4, α5, and β3 nAChR subunits; compound 3b was an inhibitor of AChE in T. cinnabarinus, and AChE was one possible target of action in T. cinnabarinus against 3b; and compound 3b may be an antagonist of nAChR and AChE in T. cinnabarinus.

Synthetic agrochemicals: a necessary clarification about their use exposure and impact in crop protection

Synthetic pesticides are largely decried. A common attitude against the synthetic agrochemicals is to avoid, criticise or ban these substances. Along with chemical pesticides to defend crops from bioagressors are microorganisms, semiochemical and natural substances used as plant protection products including biocontrol agents (BCAs) and crop protection products in organic production. Nevertheless, a natural substance status does not confer or imply safety, security or absence of residues (in the context of plant protection). Although in this paper we do not consider the toxicological perspective of highly toxic chemicals with adverse effects on humans and non-target organisms sprayed on crops, we have applied ourselves to working on the safe use of synthetic agrochemicals. Thus, along with biopesticides (either BCA or others) allowed in organic farming, we show that some synthetic chemical pesticides may be used in safe manner. HIGHLIGHTS: • Synthetic agrochemicals are widely criticised. • Some pesticide usages are not sprayed on crops. • Some biocontrol agents are of synthetic origin.