Natural products for biocontrol: review of their fate in the environment and impacts on biodiversity.

Biocontrol solutions (macroorganisms, microorganisms, natural substances, semiochemicals) are presented as potential alternatives to conventional plant protection products (PPPs) because they are supposed to have lower impacts on ecosystems and human health. However, to ensure the sustainability of biocontrol solutions, it is necessary to document the unintended effects of their use. Thus, the objectives of this work were to review (1) the available biocontrol solutions and their regulation, (2) the contamination of the environment (soil, water, air) by biocontrol solutions, (3) the fate of biocontrol solutions in the environment, (4) their ecotoxicological impacts on biodiversity, and (5) the impacts of biocontrol solutions compared to those of conventional PPPs. Very few studies concern the presence of biocontrol solutions in the environment, their fate, and their impacts on biodiversity. The most important number of results were found for the organisms that have been used the longest, and most often from the angle of their interactions with other biocontrol agents. However, the use of living organisms (microorganisms and macroorganisms) in biocontrol brings a specific dimension compared to conventional PPPs because they can survive, multiply, move, and colonize other environments. The questioning of regulation stems from this specific dimension of the use of living organisms. Concerning natural substances, the few existing results indicate that while most of them have low ecotoxicity, others have a toxicity equivalent to or greater than that of the conventional PPPs. There are almost no result regarding semiochemicals. Knowledge of the unintended effects of biocontrol solutions has proved to be very incomplete. Research remains necessary to ensure their sustainability.

Main conclusions and perspectives from the collective scientific assessment of the effects of plant protection products on biodiversity and ecosystem services along the land-sea continuum in France and French overseas territories.

Preservation of biodiversity and ecosystem services is critical for sustainable development and human well-being. However, an unprecedented erosion of biodiversity is observed and the use of plant protection products (PPP) has been identified as one of its main causes. In this context, at the request of the French Ministries responsible for the Environment, for Agriculture and for Research, a panel of 46 scientific experts ran a nearly 2-year-long (2020-2022) collective scientific assessment (CSA) of international scientific knowledge relating to the impacts of PPP on biodiversity and ecosystem services. The scope of this CSA covered the terrestrial, atmospheric, freshwater, and marine environments (with the exception of groundwater) in their continuity from the site of PPP application to the ocean, in France and French overseas territories, based on international knowledge produced on or transposable to this type of context (climate, PPP used, biodiversity present, etc.). Here, we provide a brief summary of the CSA's main conclusions, which were drawn from about 4500 international publications. Our analysis finds that PPP contaminate all environmental matrices, including biota, and cause direct and indirect ecotoxicological effects that unequivocally contribute to the decline of certain biological groups and alter certain ecosystem functions and services. Levers for action to limit PPP-driven pollution and effects on environmental compartments include local measures from plot to landscape scales and regulatory improvements. However, there are still significant gaps in knowledge regarding environmental contamination by PPPs and its effect on biodiversity and ecosystem functions and services. Perspectives and research needs are proposed to address these gaps.

Lab meets field: Accelerated selection and field monitoring concur that non-target-site-based resistance evolves first in the dicotyledonous, allergenic weed Ambrosia artemisiifolia.

Assessing weed capacity to evolve herbicide resistance before resistance occurs in the field is of major interest for chemical weed control. We used herbicide selection followed by controlled crosses to provoke accelerated evolution of resistance to imazamox (imidazolinones) and tribenuron (sulfonyurea), two acetolactate-synthase (ALS) inhibitors targeting Ambrosia artemisiifolia. In natural populations with no herbicide application records, some plants were initially resistant to metsulfuron (sulfonylurea), a cereal herbicide. Non-target-site-based resistance (NTSR) to metsulfuron was substantially increased from these plants within two generations. NTSR to imazamox and/or tribenuron emerged in metsulfuron-selected G1 progenies and was strongly reinforced in G2 progenies selected by imazamox or tribenuron. NTSR to the herbicides assayed was endowed by partly overlapping and partly specific pathways. Herbicide sensitivity bioassays conducted over 62 ALS-inhibitor-sprayed fields identified emerging resistance to imazamox and/or tribenuron in 14 A. artemisiifolia populations. Only NTSR was detected in 13 of these populations. In the last population, NTSR was present together with a mutant, herbicide-resistant ALS allele bearing an Ala-205-Thr substitution. NTSR was thus by far the predominant type of resistance to ALS inhibitors in France. This confirmed accelerated selection results and demonstrated the relevance of this approach to anticipate resistance evolution in a dicotyledonous weed.

Uncovering the genomic basis of an extraordinary plant invasion.

Invasive species are a key driver of the global biodiversity crisis, but the drivers of invasiveness, including the role of pathogens, remain debated. We investigated the genomic basis of invasiveness in Ambrosia artemisiifolia (common ragweed), introduced to Europe in the late 19th century, by resequencing 655 ragweed genomes, including 308 herbarium specimens collected up to 190 years ago. In invasive European populations, we found selection signatures in defense genes and lower prevalence of disease-inducing plant pathogens. Together with temporal changes in population structure associated with introgression from closely related Ambrosia species, escape from specific microbial enemies likely favored the plant's remarkable success as an invasive species.

Geographical variation in resistance to acetyl-coenzyme A carboxylase-inhibiting herbicides across the range of the arable weed Alopecurus myosuroides (black-grass).

*The geographical structure of resistance to herbicides inhibiting acetyl-coenzyme A carboxylase (ACCase) was investigated in the weed Alopecurus myosuroides (black-grass) across its geographical range to gain insight into the process of plant adaptation in response to anthropogenic selective pressures occurring in agricultural ecosystems. *We analysed 297 populations distributed across six countries in A. myosuroides' main area of occupancy. The frequencies of plants resistant to two broadly used ACCase inhibitors and of seven mutant, resistant ACCase alleles were assessed using bioassays and genotyping, respectively. *Most of the resistance was not endowed by mutant ACCase alleles. Resistance and ACCase allele distribution patterns were characterized by mosaicism. The prevalence of resistance and of ACCase alleles differed among countries. *Resistance clearly evolved by redundant evolution of a set of resistance alleles or genes, most of which remain unidentified. Resistance in A. myosuroides was shaped by variation in the herbicide selective pressure at both the individual field level and the national level.

Which Traits Make Weeds More Successful in Maize Crops? Insights from a Three-Decade Monitoring in France.

A major aim in invasion biology is identifying traits distinguishing alien invasive and alien non-invasive plants. Surprisingly, this approach has been, so far, poorly used to understand why some arable weeds are abundant and widespread while others are rare and narrowly distributed. In the present study, we focused on the characteristics of successful weeds occurring in maize fields, one of the most important crops worldwide. Two national weed surveys conducted in France were used to identify increasing and decreasing species based on 175 and 484 surveyed fields in the 1970s and the 2000s, respectively. Weed trait values related to regional frequency, local abundance, and specialization to maize were identified with phylogenetic generalized least-squares (PGLS). We found a positive relationship between regional frequency and local abundance, i.e., the most widespread weeds were also locally more abundant. We highlighted that weeds with the C4 photosynthetic pathway and summer emergence were more abundant, more frequent, and more specialized to maize crops. More generally, we highlighted two successful strategies: On the one hand, traits related to a general weediness syndrome with rapid resource acquisition (high SLA and Ellenberg-N) and high colonization capacity (seed longevity, fecundity, and wind dispersal); on the other hand, traits related to specific adaptation to spring cultivation (thermophilous species with summer emergence, late flowering, and C4 photosynthetic pathway). Deviations from the abundancy-frequency relationships also indicated that species of the Panicoideae sub-family, species with Triazine-resistant populations, and neophyte species were more abundant than expected by their regional frequency. To some extent, it is therefore possible to predict which species can be troublesome in maize crops and use this information in weed risk assessment tools to prevent new introductions or favor early detection and eradication. This study showed how tools developed in functional and macro-ecology can be used to improve our understanding of weed ecology and to develop more preventive management strategies.

Estimation of pollen and seed production of common ragweed in France.

Common ragweed (Ambrosia artemisiifolia L.) is an invasive weed of field crops and human-disturbed habitats in Europe. As well as in its natural range (North America), common ragweed is a threat to human health due to its abundant allergenic pollen release. Most studies have been focused on airborne pollen monitoring, but to date, no data have been available on precise individual plant pollen and seed production related to plant traits growing in natural environment and on their corresponding source of variation. The aim of this study was to evaluate pollen and seed production of common ragweed plants in several populations in France. Seasonal pollen production per plant ranged from 100 million to 3 billion and seed production from 346 to 6,114, depending on plant size and habitat. Common ragweed plants developing in field crops produced more pollens and seeds than those growing in other habitats. Pollen and seed production was closely related to plant volume and biomass, thus providing a means of estimating potential pollen and seed production in given target areas. Such biological data could be integrated into population management strategies or into airborne pollen modelling.

New gSSR and EST-SSR markers reveal high genetic diversity in the invasive plant Ambrosia artemisiifolia L. and can be transferred to other invasive Ambrosia species.

Ambrosia artemisiifolia L., (common ragweed), is an annual invasive and highly troublesome plant species originating from North America that has become widespread across Europe. New sets of genomic and expressed sequence tag (EST) based simple sequence repeats (SSRs) markers were developed in this species using three approaches. After validation, 13 genomic SSRs and 13 EST-SSRs were retained and used to characterize the genetic diversity and population genetic structure of Ambrosia artemisiifolia populations from the native (North America) and invasive (Europe) ranges of the species. Analysing the mating system based on maternal families did not reveal any departure from complete allogamy and excess homozygosity was mostly due the presence of null alleles. High genetic diversity and patterns of genetic structure in Europe suggest two main introduction events followed by secondary colonization events. Cross-species transferability of the newly developed markers to other invasive species of the Ambrosia genus was assessed. Sixty-five percent and 75% of markers, respectively, were transferable from A. artemisiifolia to Ambrosia psilostachya and Ambrosia tenuifolia. 40% were transferable to Ambrosia trifida, this latter species being seemingly more phylogenetically distantly related to A. artemisiifolia than the former two.

Investigation of Amino Acids As Herbicides for Control of Orobanche minor Parasitism in Red Clover.

Certain amino acids induce inhibitory effects in plant growth due to feedback inhibition of metabolic pathways. The inhibition patterns depend on plant species and the plant developmental stage. Those amino acids with inhibitory action on specific weeds could be utilized as herbicides, however, their use for weed control has not been put into practice. Orobanche minor is a weed that parasitizes red clover. O. minor germination is stimulated by clover root exudates. The subsequent seedling is an obligated parasite that must attach quickly to the clover root to withdraw its nutrients. Early development of O. minor is vulnerable to amino acid inhibition and therefore, a series of in vitro, rhizotron, and field experiments were conducted to investigate the potential of amino acids to inhibit O. minor parasitism. In in vitro experiments it was found that among a collection of 20 protein amino acids, lysine, methionine and tryptophan strongly interfere with O. minor early development. Field research confirmed their inhibitory effect but revealed that methionine was more effective than lysine and tryptophan, and that two successive methionine applications at 308 and 543 growing degree days inhibited O. minor emergence in red clover up to 67%. We investigated additional effects with potential to influence the practical use of amino acids against broomrape weeds, whether the herbicidal effect may be reversible by other amino acids exuded by host plants or may be amplified by inducing host resistance barriers against O. minor penetration. This paper suggests that amino acids may have the potential to be integrated into biorational programs of broomrape management.

Choosing the best cropping systems to target pleiotropic effects when managing single-gene herbicide resistance in grass weeds. A blackgrass simulation study.

BACKGROUND: Managing herbicide-resistant weeds is becoming increasingly difficult. Here we adapted the weed dynamics model AlomySys to account for experimentally measured fitness costs linked to mutants of target-site resistance to acetyl-coenzyme A carboxylase (ACCase)-inhibiting herbicides in Alopecurus myosuroides. We ran simulations to test how effectively cultural practices manage resistance. RESULTS: Simulations of an oilseed rape/winter wheat/winter barley rotation showed that, when replacing one of the seven applied herbicides with an ACCase-inhibiting one, resistant mutants exceeded 1 plant m(-2) , with a probability of 40%, after an average of 18 years. This threshold was always exceeded when three or four ACCase-inhibiting herbicides were used, after an average of 8 and 6 years respectively. With reduced herbicide rates or suboptimal spraying conditions, resistance occurred 1-3 years earlier in 50% of simulations. Adding spring pea to the rotation or yearly mouldboard ploughing delayed resistance indefinitely in 90 and 60% of simulations respectively. Ploughing also modified the genetic composition of the resistant population by selecting a previously rare mutant that presented improved pre-emergent growth. The prevalence of the mutations was influenced more by their associated fitness cost or benefit than by the number of ACCase-inhibiting herbicides to which they conferred resistance. CONCLUSION: Simulations allowed us to rank weed management practices and suggest that pleiotropic effects are extremely important for understanding the frequency of herbicide resistance in the population. © 2016 Society of Chemical Industry.

[Ragweed (Ambrosia artemisiifolia L.): expansion history of a "biological pollutant" in France]. / L'ambroisie: chronique de l'extension d'un "polluant biologique" en France.

In France, common ragweed (Ambrosia artemisiifolia L.) is an invasive species, which most probably originates from North America. This plant is responsible for human health problems as the pollen causes allergic rhinitis and seasonal asthma; in addition, it engenders agronomical problems as the efficient herbicide treatments are few. Consequently, various departments of the Rhône-Alpes region set up eradication programs for common ragweed. The species is distributed over a large range of ecological environments (road margins, embankments, river beds) and does not seem to be dependent on soil properties. Its ability to occupy different environments varies with the geographic location. Common ragweed was cultivated in botanical gardens during the XVIIIth century but seems to have arrived in France in seed lots during the XIXth century. It therefore began its "invasion" as a crop weed. Because of its late emergence date (late March), common ragweed is most frequently found in spring crops as well as during the inter-crop season. Its "natural" dispersal mechanisms are rudimentary; its seeds are probably dispersed mostly during the transport of material (soil, gravel, compost...), irrigation and especially via harvest combines. The development history of this species in France is scarcely known. The examination of herbarium collections helped to partially reconstruct the history of the species. According to the first results, the species arrived in several locations and at different dates in France. However, common ragweed spread most successfully in the Lyons region because of reasons still unknown.

DNA analysis of herbarium Specimens of the grass weed Alopecurus myosuroides reveals herbicide resistance pre-dated herbicides.

Acetyl-CoA carboxylase (ACCase) alleles carrying one point mutation that confers resistance to herbicides have been identified in arable grass weed populations where resistance has evolved under the selective pressure of herbicides. In an effort to determine whether herbicide resistance evolves from newly arisen mutations or from standing genetic variation in weed populations, we used herbarium specimens of the grass weed Alopecurus myosuroides to seek mutant ACCase alleles carrying an isoleucine-to-leucine substitution at codon 1781 that endows herbicide resistance. These specimens had been collected between 1788 and 1975, i.e., prior to the commercial release of herbicides inhibiting ACCase. Among the 734 specimens investigated, 685 yielded DNA suitable for PCR. Genotyping the ACCase locus using the derived Cleaved Amplified Polymorphic Sequence (dCAPS) technique identified one heterozygous mutant specimen that had been collected in 1888. Occurrence of a mutant codon encoding a leucine residue at codon 1781 at the heterozygous state was confirmed in this specimen by sequencing, clearly demonstrating that resistance to herbicides can pre-date herbicides in weeds. We conclude that point mutations endowing resistance to herbicides without having associated deleterious pleiotropic effects can be present in weed populations as part of their standing genetic variation, in frequencies higher than the mutation frequency, thereby facilitating their subsequent selection by herbicide applications.

Variability and cryptic heteromorphism of Ambrosia artemisiifolia seeds: What consequences for its invasion in France?

BACKGROUND AND AIMS: Ambrosia artemisiifolia is a ruderal weed introduced from North America to Europe. It produces large amount of achenes which are highly heterogeneous in size. Due to the preponderant role of propagules in invasive plant processes, the achene mass variability related to germination, dispersal strategy and life history traits of offspring were investigated within this species. METHODS: The variability in achene mass was quantified among six populations sampled in different habitats. The effects of achene mass variation on germination were studied. The percentages of floating and non-floating achenes were evaluated in the studied populations. The consequences of floatability on the growth and traits of the offspring were studied. KEY RESULTS: Mean achene mass ranged from 1.72 to 3.60 mg, depending on the populations, and was highly variable. Variation among achenes within plants accounted for 63.9 % of the variance, whereas variances among plants within each population (22.2 %) and among populations (13.9 %) were lower. Achene masses were also positively correlated to the total germination percentage for four populations out of six. Two kinds of achenes were distinguished: floating and non-floating. The majority of floating achenes (90 %) sank 24 h after water immersion. Whatever the population, floating achenes were lighter, more dormant and germinated faster than non-floating achenes. Plants which issued from floating achenes had better growth than those from non-floating achenes. CONCLUSIONS: The capacity of A. artemisiifolia to be invasive in Europe appears to be high, possibly due to its huge plasticity in seed mass which may help it to cope with a wide range of conditions and to establish in disturbed habitats. Furthermore, the recent invasion of southern France by A. artemisiifolia could be partially explained by water dispersal of achenes through rivers and has pinpointed its colonization potential along French rivers.