Soil microbial community fragmentation reveals indirect effects of fungicide exposure mediated by biotic interactions between microorganisms.

Fungicides are used worldwide to improve crop yields, but they can affect non-target soil microorganisms which are essential for ecosystem functioning. Microorganisms form complex communities characterized by a myriad of interspecies interactions, yet it remains unclear to what extent non-target microorganisms are indirectly affected by fungicides through biotic interactions with sensitive taxa. To quantify such indirect effects, we fragmented a soil microbial community by filtration to alter biotic interactions and compared the effect of the fungicide hymexazol between fractions in soil microcosms. We postulated that OTUs which are indirectly affected would exhibit a different response to the fungicide across the fragmented communities. We found that hymexazol primarily affected bacterial and fungal communities through indirect effects, which were responsible for more than 75% of the shifts in relative abundance of the dominant microbial OTUs after exposure to an agronomic dose of hymexazol. However, these indirect effects decreased for the bacterial community when hymexazol doses increased. Our results also suggest that N-cycling processes such as ammonia oxidation can be impacted indirectly by fungicide application. This work sheds light on the indirect impact of fungicide exposure on soil microorganisms through biotic interactions, which underscores the need for higher-tier risk assessment. ENVIRONMENTAL IMPLICATION: In this study, we used a novel approach based on the fragmentation of the soil microbial community to determine to which extent fungicide application could indirectly affect fungi and bacteria through biotic interactions. To assess off-target effects of fungicide on soil microorganisms, we selected hymexazol, which is used worldwide to control a variety of fungal plant pathogens, and exposed arable soil to the recommended field rate, as well as to higher rates. Our findings show that at least 75% of hymexazol-impacted microbial OTUs were indirectly affected, therefore emphasizing the importance of tiered risk assessment.

Early Assessment of Biodegradability of Small Molecules to Support the Chemical Design in Agro & Pharma R&D.

The use of agrochemical and pharmaceutical active ingredients is essential in our modern society. Given the increased concern and awareness of the potential risks of some chemicals, there is a growing need to align with 'green chemistry' and 'safe and sustainable by design' principles and thus to evaluate the hazards of agrochemical and pharmaceutical active ingredients in early stages of R&D. We give an overview of the current challenges and opportunities to assess the principle of biodegradability in the environment. Development of new medium/high-throughput methodologies, combining predictive tools and wet-lab experimentation are essential to design biodegradable chemicals early in the active ingredient discovery and selection process.

The Soil Microbiota Recovery in the Agroecosystem: Minimal Information and a New Framework for Sustainable Agriculture.

The efficient management of soil represents a mission of vital importance for meeting the continuously increasing agricultural demand in a sustainable way. Decades of research identified in the biotechnological potential of soil microorganisms an always more practicable channel for achieving these goals. Due to the complexity of soil microbial communities and their tight connection to soil characteristics, it is still difficult to define universal strategies for an efficient and sustainable agroecosystem management. We here propose a new framework for the assessment of the impact of agricultural practices in the agroecosystem that revolves around the concept of microbial community recovery. This assessment is based on the selection of (i) a representative temporal interval, (ii) a representative agricultural system and (iii) monitoring tools able to assess the expression levels of microbial functionality in soil. This approach can be especially valuable for evaluating the effects of agrochemicals and other agronomical amendments (of different nature: biological, physical, chemical) on the soil microbiota. In the same way precision-medicine tries to tailor drugs on an always smaller subset of patients' characteristics, a new generation of agrochemicals can be developed and tested considering soil characteristics in order to minimize their off-target effects. What remains central in this paradigm is the promotion of Soil Health maintenance practices. As for healthy humans, a healthy soil is more resilient and tolerates treatments and stresses better while recovering more quickly.

Comparison of Small Molecule Biotransformation Half-Lives between Activated Sludge and Soil: Opportunities for Read-Across?

Compartment-specific degradation half-lives are essential pieces of information in the regulatory risk assessment of synthetic chemicals. However, their measurement according to regulatory testing guidelines is laborious and costly. Despite the obvious ecological and economic benefits of knowing environmental degradability as early as possible, its consideration in the early phases of rational chemical design is therefore challenging. Here, we explore the possibility to use half-lives determined in highly time- and work-efficient biotransformation experiments with activated sludge and mixtures of chemicals to predict soil half-lives from regulatory simulation studies. We experimentally determined half-lives for 52 structurally diverse agrochemical active ingredients in batch reactors with three concentrations of the same activated sludge. We then developed bi- and multivariate models for predicting half-lives in soil by regressing the experimentally determined half-lives in activated sludge against average soil half-lives of the same chemicals extracted from regulatory data. The models differed in how we accounted for sorption-related bioavailability differences in soil and activated sludge. The best-performing models exhibited good coefficients of determination (R2 of around 0.8) and low average errors (

Science and application of strigolactones.

Strigolactones (SLs) represent a class of plant hormones that regulate developmental processes and play a role in the response of plants to various biotic and abiotic stresses. Both in planta hormonal roles and ex planta signalling effects of SLs are potentially interesting agricultural targets. In this review, we explore various aspects of SL function and highlight distinct areas of agriculture that may benefit from the use of synthetic SL analogues, and we identify possible bottlenecks. Our objective is to identify where the contributions of science and stakeholders are still needed to achieve harnessing the benefits of SLs for a sustainable agriculture of the near future.

Design, Synthesis and Biological Evaluation of Strigolactone and Strigolactam Derivatives for Potential Crop Enhancement Applications in Modern Agriculture.

Strigolactones have been known as signaling molecules in the rhizosphere of plants since more than 50 years. However, their roles as phytohormone have been only recognized since 2008. We describe here a very efficient synthetic access to representative canonical strigolactones displaying the A-B-C-D tetracyclic structure and to non-canonical strigolactones as carlactonoic acid and methyl carlactonoate. In addition, we report the design and the synthesis of strigolactams as promising derivatives of strigolactones for potential use in modern agriculture. Among the synthetic methods developed for this project, the intramolecular [2+2] cycloaddition of keteneiminium salts to C=C bond has been particularly useful to the synthesis of natural strigolactones and their potentially improved analogues.

Strigolactones: Plant Hormones with Promising Features.

Almost 80 years after the discovery of the first plant hormone, auxin, a few years ago a new class of plant hormones, the strigolactones, was discovered. These molecules have unprecedented biological activity in a number of highly important biological processes in plants but also outside the plant in the rhizosphere, the layer of soil surrounding the roots of plants and teeming with life. The exploitation of this amazing biological activity is not without challenges: the synthesis of strigolactones is complicated and designing the desired activity a difficult task. This minireview describes the current state of knowledge about the strigolactones and how synthetic analogs can be developed that can potentially contribute to the development of a sustainable agriculture.

Comparison of visible imaging, thermography and spectrometry methods to evaluate the effect of Heterodera schachtii inoculation on sugar beets.

BACKGROUND: Phenotyping technologies are expected to provide predictive power for a range of applications in plant and crop sciences. Here, we use the disease pressure of Beet Cyst Nematodes (BCN) on sugar beet as an illustrative example to test the specific capabilities of different methods. Strong links between the above and belowground parts of sugar beet plants have made BCN suitable targets for use of non-destructive phenotyping methods. We compared the ability of visible light imaging, thermography and spectrometry to evaluate the effect of BCN on the growth of sugar beet plants. RESULTS: Two microplot experiments were sown with the nematode susceptible cultivar Aimanta and the nematode tolerant cultivar BlueFox under semi-field conditions. Visible imaging, thermal imaging and spectrometry were carried out on BCN infested and non-infested plants at different times during the plant development. Effects of a chemical nematicide were also evaluated using the three phenotyping methods. Leaf and beet biomass were measured at harvest. For both susceptible and tolerant cultivar, canopy area extracted from visible images was the earliest nematode stress indicator. Using such canopy area parameter, delay in leaf growth as well as benefit from a chemical nematicide could be detected already 15 days after sowing. Spectrometry was suitable to identify the stress even when the canopy reached full coverage. Thermography could only detect stress on the susceptible cultivar. Spectral Vegetation Indices related to canopy cover (NDVI and MCARI2) and chlorophyll content (CHLG) were correlated with the final yield (R = 0.69 on average for the susceptible cultivar) and the final nematode population in the soil (R = 0.78 on average for the susceptible cultivar). CONCLUSION: In this paper we compare the use of visible imaging, thermography and spectrometry over two cultivars and 2 years under outdoor conditions. The three different techniques have their specific strengths in identifying BCN symptoms according to the type of cultivars and the growth stages of the sugar beet plants. Early detection of nematicide benefit and high yield predictability using visible imaging and spectrometry suggests promising applications for agricultural research and precision agriculture.

Zealactones. Novel natural strigolactones from maize.

In the root exudate and root extracts of maize hybrid cv NK Falkone seven putative strigolactones were detected using UPLC-TQ-MS-MS. All seven compounds displayed MS-MS-fragmentation common for strigolactones and particularly the presence of a fragment of m/z 97 Da, which may indicate the presence of the so-called D-ring, suggests they are strigolactones. The levels of all these putative strigolactones increased upon phosphate starvation and decreased upon fluridone (carotenoid biosynthesis inhibitor) treatment, both of which are a common response for strigolactones. All seven compounds were subsequently isolated with prep-HPLC-MS. They all exhibited Striga hermonthica seed germination inducing activity just as the synthetic strigolactone analog GR24. The structure of two of the seven compounds was elucidated by NMR spectroscopy as: methyl (2E,3E)-4-(3,3-dimethyl-5-oxo-2-(prop-1-en-2-yl)tetrahydrofuran-2-yl)-2-(((4-methyl-5-oxo-2,5-dihydrofuran-2-yl)oxy)methylene)but-3-enoate (two diastereomers 1a and 1b). Strigolactones (1a/b) are closely related to the methyl ester of carlactonoic acid (MeCLA) and heliolactone. However, they contain a unique 4,4-dimethyltetrahydrofuran-2-one motif as the "A-ring" instead of the classical (di)methylcyclohexene. Because these compounds were isolated from maize (Zea mays) we called them "zealactone 1a and 1b". The implications of this discovery for our view on strigolactones and their biosynthesis are discussed.

Strigolactone derivatives for potential crop enhancement applications.

New technologies able to mitigate the main abiotic stresses (i.e., drought, salinity, cold and heat) represent a substantial opportunity to contribute to a sustainable increase of agricultural production. In this context, the recently discovered phytohormone strigolactone is an important area of study which can underpin the quest for new anti-stress technologies. The pleiotropic roles played by strigolactones in plant growth/development and in plant adaptation to environmental changes can pave the way for new innovative crop enhancement applications. Although a significant scientific effort has been dedicated to the strigolactone subject, an updated review with emphasis on the crop protection perspective was missing. This paper aims to analyze the advancement in different areas of the strigolactone domain and the implications for agronomical applications.

Simplified strigolactams as potent analogues of strigolactones for the seed germination induction of Orobanche cumana Wallr.

BACKGROUND: Strigolactones play an important role in the rhizosphere as signalling molecules stimulating the seed germination of parasitic weed seeds and hyphal branching of arbuscular micorrhiza, and also act as hormones in plant roots and shoots. Strigolactone derivatives, e.g. strigolactams, could be used as suicidal germination inducers in the absence of a host crop for the decontamination of land infested with parasitic weed seeds. RESULTS: We report the stereoselective synthesis of novel strigolactams, together with some of their critical physicochemical properties, such as water solubility, hydrolytic stability, as well as their short soil persistence. In addition, we show that such strigolactams are potent germination stimulants of O. cumana parasitic weed seeds and do not affect the seed germination and the root growth of sunflower. CONCLUSIONS: The novel strigolactam derivatives described here compare favourably with the corresponding GR-28 strigolactones in terms of biological activity and physicochemical properties. However, we believe strigolactone and strigolactam derivatives require further structural optimisation to improve their soil persistence to demonstrate a potential for agronomical applications. © 2016 Society of Chemical Industry.

Strigolactam: New potent strigolactone analogues for the germination of Orobanche cumana.

Very recently, strigolactones have been conclusively identified as phytohormones. The progresses achieved in this field are culminating in the identification of the molecular receptors involved in the signal transduction mechanism. The exact mechanism of the mode of action of strigolactones still remains to be fully elucidated and we were interested to gain some insight into the mechanism of action of strigolactones by selectively modifying the reactivity of the lactone C-ring. Therefore, we report here the synthesis of strigolactams 1 and 16 and their surprisingly good activity on the germination of Orobanche cumana parasitic weed seeds.

Chemicals inducing seed germination and early seedling development.

Seed germination and early seedling development are essential events in the plant life cycle that are controlled largely by the interplay and cross-talk between several plant hormones. Recently, major progress has been achieved in the elucidation at the molecular level of the signalling of these phytohormones. In this review, we summarise the data for the most promising classes of compounds, which could find potential agronomic applications for promoting seed germination and early seedling development even under abiotic stress conditions. Structural modifications of plant hormones are required to improve their biological performance and their specificity to allow commercial application.