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This study evaluates the capacity of commercial formulations of synthetic fungicides to inhibit grapevine bacterial growth when sprayed on vineyards to control diseases, such as downy mildew, powdery mildew and secondary rots. Fungicide sensitivity plate assays were carried out on bacteria isolated from vineyards that were also identified and characterized for their plant growth-promoting (PGP) traits and antifungal activity. The high taxonomic variability of bacteria screened with different chemical classes of fungicides is one new finding of this study. Seven out of 11 fungicides were able to inhibit the growth of bacteria at a concentration corresponding to the maximum dose allowed by law in spray treatments of vineyards. Bacterial sensitivity to each fungicide varied greatly. Many sensitive isolates displayed PGP traits and/or antagonistic activity. This study shows the potential impact of fungicidal treatments on grapevine bacterial microbiota. The involvement of bacteria beneficial to the growth and health of plants underlines the importance of this investigation. Our data reveal that the control of a certain disease may be possible using fungicides that have no or low impact on natural non-target microbiota. Understanding the action mechanisms of the active ingredients in these products is a priority for the development of new eco-friendly pesticides. Highlights: Effects of synthetic fungicides on grapevine bacteria were analyzed. Plant growth promoting (PGP) traits and antifungal activity of strains were assayed. Great variability was observed among bacteria regarding fungicide sensitivity. Many sensitive strains had PGP traits and antifungal activity. Potential impact of fungicides on grapevine bacterial microbiota. [ABSTRACT FROM AUTHOR]

Conventional agriculture still relies on the general use of agrochemicals (herbicides, fungicides and insecticides) to control various pests (weeds, fungal pathogens and insects), to ensure the yield of crop and to feed a constantly growing population. The generalized use of pesticides in agriculture leads to the contamination of soil and other connected environmental resources. The persistence of pesticide residues in soil is identified as a major threat for in-soil living organisms that are supporting an important number of ecosystem services. Although authorities released pesticides on the market only after their careful and thorough evaluation, the risk assessment for in-soil living organisms is unsatisfactory, particularly for microorganisms for which pesticide toxicity is solely considered by one global test measuring N mineralization. Recently, European Food Safety Authority (EFSA) underlined the lack of standardized methods to assess pesticide ecotoxicological effects on soil microorganisms. Within this context, there is an obvious need to develop innovative microbial markers sensitive to pesticide exposure. Biomarkers that reveal direct effects of pesticides on microorganisms are often viewed as the panacea. Such biomarkers can only be developed for pesticides having a mode of action inhibiting a specific enzyme not only found in the targeted organisms but also in microorganisms which are considered as "non-target organisms" by current regulations. This review explores possible ways of innovation to develop such biomarkers for herbicides. We scanned the herbicide classification by considering the mode of action, the targeted enzyme and the ecotoxicological effects of each class of active substance in order to identify those that can be tracked using sensitive microbial markers. Unlabelled Image • Herbicide mode of action is depicted according to the HRAC classification. • Numerous herbicides target an enzyme found in plants and in microorganisms. • Possible effects of herbicides on soil microbial communities are described. • Targeted microbial enzymes are suggested to be used as exposure biomarkers. [ABSTRACT FROM AUTHOR]

Grasslands include some of the most endangered and less protected ecosystems on the planet, such as the Pampa of South America. In the Flooding Pampa where native grasslands were not replaced by crops, glyphosate is frequently sprayed in late-summer every year to increase winter forage productivity for cattle without knowing the impacts on both aboveground and belowground grassland genetic resources. Here, we evaluated the effect of this practice on the abundance and community structure of members of the genus Pseudomonas , one of the most diverse bacterial taxa of the plant rhizosphere broadly recognized by their benefits on plant growth and protection, and on soil remediation. In a field experiment, we analyzed the impact of a single application or of a repeated annual application during 4 consecutive years of the recommended dose of commercial glyphosate (Glacoxan®, 3 l ha-1 and 1440 g active ingredient ha-1). In a greenhouse experiment, we tested whether exposure of bare soil to either commercially formulated or pure glyphosate has a direct impact on the resident pseudomonas community in the absence of plants. In the field, we found that the repeated annual herbicide application resulted in a reduction in the abundance and a shift in the community structure of culturable pseudomonads, with evidence of an enrichment of glyphosate-metabolizing lineages. On the other hand, a single application of glyphosate to bare soil under greenhouse conditions did not affect the abundance nor the community structure of pseudomonads. Considering that these plant-beneficial bacteria are natural inhabitants of the rhizosphere and that their fitness is promoted by plant root exudates, the observed alterations are most likely associated with the drop in the vegetation cover directly provoked by the effect of glyphosate. For the first time, we report on the consequences that a reiterated glyphosate application has on a diverse soil reservoir of bacteria that contributes to crucial ecosystem functions in a temperate natural grassland under animal production. Our findings strengthen the notion that this agronomical practice has an unavoidable imprint on non-target microorganisms that are relevant components of the plant-soil feedbacks and that may be instrumental for ecosystem restoration. We conclude that it is necessary to develop sustainable management practices to avoid affecting key functional microorganisms and exploit their contributions to society. • Glyphosate application (GA) is used to increase grassland quality and productivity for livestock. • Repeated annual GA in the field reduced the abundance of soil culturable pseudomonads. • Repeated annual GA in the field enriched the community with glyphosate-metabolizing ecotypes. • Plant cover was negatively correlated with abundance of soil culturable pseudomonads. • A single GA to bare soil did not affect load nor community structure of pseudomonads. [ABSTRACT FROM AUTHOR]