Arbuscular mycorrhizal fungi and their response to pesticides

Sublethal pesticide exposure in non-target terrestrial ecosystems: from known effects on individuals to potential consequences on trophic interactions and network functioning

Over the last decades, the intensification of agriculture has resulted in an increasing use of pesticides, which has led to widespread contamination of non-target ecosystems in agricultural landscapes. Plants and arthropods inhabiting these systems are therefore chronically exposed to, at least, low levels of pesticides through direct pesticide drift, but also through the contamination of their nutrient sources (e.g. soil water or host/prey tissues). Pesticides (herbicides, acaricides/insecticides and fungicides) are chemical substances used to control pests, such as weeds, phytophagous arthropods and pathogenic microorganisms. These molecules are designed to disturb specific physiological mechanisms and induce mortality in targeted organisms. However, under sublethal exposure, pesticides also affect biological processes including metabolism, development, reproduction or inter-specific interactions even in organisms that do not possess the molecular target of the pesticide. Despite the broad current knowledge on sublethal effects of pesticides on organisms, their adverse effects on trophic interactions are less investigated, especially within terrestrial trophic networks. In this review, we provide an overview of the effects, both target and non-target, of sublethal exposures to pesticides on traits involved in trophic interactions between plants, phytophagous insects and their natural enemies. We also discuss how these effects may impact ecosystem functioning by analyzing studies investigating the responses of Plant-Phytophage-Natural enemy trophic networks to pesticides. Finally, we highlight the current challenges and research prospects in the understanding of the effects of pesticides on trophic interactions and networks in non-target terrestrial ecosystems.

Ranking environmental and edaphic attributes driving soil microbial community structure and activity with special attention to spatial and temporal scales

The incredibly complex soil microbial communities at small scales make their analysis and identification of reasons for the observed structures challenging. Microbial community structure is mainly a result of the inoculum (dispersal), the selective advantages of those organisms under the habitat-based environmental attributes, and the ability of those colonizers to sustain themselves over time. Since soil is protective, and its microbial inhabitants have long adapted to varied soil conditions, significant portions of the soil microbial community structure are likely stable. Hence, a substantial portion of the community will not correlate to often measured soil attributes. We suggest that the drivers be ranked on the basis of their importance to the fundamental needs of the microbes: (i) those that supply energy, i.e., organic carbon and electron acceptors; (ii) environmental effectors or stressors, i.e., pH, salt, drought, and toxic chemicals; (iii) macro-organism associations, i.e., plants and their seasonality, animals and their fecal matter, and soil fauna; and (iv) nutrients, in order, N, P, and probably of lesser importance, other micronutrients, and metals. The relevance of drivers also varies with spatial and time scales, for example, aggregate to field to regional, and persistent to dynamic populations to transcripts, and with the extent of phylogenetic difference, hence phenotypic differences in organismal groups. We present a summary matrix to provide guidance on which drivers are important for particular studies, with special emphasis on a wide range of spatial and temporal scales, and illustrate this with genomic and population (rRNA gene) data from selected studies.

Effects of mixtures of herbicides on nutrient cycling and plant support considering current agriculture practices

The use of mixtures of pesticides and consecutive pesticide applications challenge current regulations aimed at protecting ecosystem health due to unpredictable effects of complex and dynamic mixtures. In this study, we tested the ecotoxicological effects of mixtures of herbicides, applied following a real application scheme of soybean production on soil health in a mesocosm experiment. The experiment included two sequential applications; first, glyphosate + dicamba + clethodim, and 30 days later, flumioxazin + metolachlor. Commercial products were used at the recommended doses and at two other concentrations: half and double the recommended dose. Soybean plants were exposed to the herbicide-contaminated soil from the time of sowing to the beginning of pod formation. Half of the plants were harvested at the vegetative stage and the remaining plants at the reproductive stage to evaluate endpoints related to plant support and nutrient cycling. Plant biomass was significantly affected during the vegetative stage at the recommended and double the recommended dose, with the effects being mixture-dose dependent. Lower total and arbuscular colonization of mycorrhizas were also observed in double the recommended dose, and intermediate results were observed for the recommended dose. Nodule mass and phosphorous concentration in plants decreased with increasing herbicide doses. By the end of the experiment, nodule mass and total mycorrhizal colonization were low in the plants treated with double the recommended dose of herbicides. However, both endpoints reached similar values to the control at lower herbicide doses. Plant height and phenology were only lower at double the recommended dose during the experiment. The use of non-standard endpoints evidenced that important soil functions were transiently or permanently affected, while the realistic application scheme accounted for the impact of the management practice currently used. Pesticide risk assessment should therefore, incorporate both issues to effectively protect the ecosystems.

Occurrence, multiphase partitioning, drivers, and ecological risks of current-use herbicides in a river basin dominated by rice-vegetable rotations in tropical China

Rice-vegetable rotation practices prevail in subtropical and tropical agriculture worldwide, with applications of current-use herbicides (CUHs) vital for nontarget plant control. After application, CUHs migrate to environmental compartments, where the occurrence, fate, and ecological risks have not been well characterized. To further understand the occurrence and multiphase partitioning, as well as to evaluate potential drivers and mixture risks in environmental compartments, we analyzed 11 CUHs in 576 samples from 36 rice-vegetable rotations in Nandu River basin, Hainan, China. Samples included soil, water, suspended particulate matter, and sediment collected during both rice and vegetable planting periods. The CUH concentrations varied across environmental compartments, but with high levels of glyphosate and aminomethylphosphonic acid organophosphorus herbicides (OPHs) frequently detected, accounting for 82.3 % to 99.0 % in environmental compartments. Phenoxy acid (PAA) and chloroacetanilide (ANH) herbicides were detected at lower frequencies. Spatiotemporal variation was significantly different among OPHs, ANHs, and PAAs, with geographic and crop-related patterns most evident for CUHs rather than OPHs. Structural equation model, redundancy, and boosted regression tree analyses indicated environmental compartment properties (pH, organic matter, and Fe/Al oxides), crop type, and wet/dry climate were important drivers of spatiotemporal patterns. Fugacity ratios indicated multiphase partitioning and transport of CUHs differed in rice and vegetable planting periods. A new assessment framework based on species-sensitive distributions and environmental compartment weight index indicated unacceptable risks of CUHs (risk quotient >1 in >50 % of sites), with most risks from OPHs (10.5 % to 98.0 %) and butachlor, acetochlor, and 2,4-dichlorophenoxyacetic acid. Risk hot spots were identified as the soil, the central region, and the vegetable planting period, potentially threatening nontarget organisms (e.g., Lemna minor, Glomus intraradices, and Apis mellifera). This study provides a new risk assessment framework and demonstrates the domination of OPHs in CUH contamination and risks in the tropics, thus helping guide policymakers and stakeholders on herbicide management.

Soil enzyme activities, physiological indicators, agronomic traits and yield of common buckwheat under herbicide combined with safeners

In the pursuit of green agricultural development, alleviating the harmful effects of herbicides is critical. Herbicide safeners have been identified as an effective solution to safeguard crops without compromising the herbicidal efficacy. However, the impact of combined applications of herbicide and safeners on the physiological characteristics, growth, yield of common buckwheat, and soil enzyme activities remains unclear. Therefore, a two-year (2021 and 2022) field experiment was conducted in the Loess Plateau region of Northwest China under seven treatments: herbicide metolachlor application alone (H1); herbicide metolachlor combined with gibberellin (H1S1); herbicide metolachlor combined with brassinolide (H1S2); herbicide metolachlor combined with naian (H1S3); herbicide metolachlor combined with jiecaotong (H1S4); manual weeding (CK1) and spraying the same volume of water (CK2). The results indicated that H1S3 minimized herbicide toxicity while sustaining the herbicide control efficacy. H1S2 treatment significantly increased the chlorophyll content (SPAD value), superoxide dismutase (SOD), peroxidase (POD) activities, and decreased the malondialdehyde (MDA) content of the leaves compared to H1 treatment. Additionally, the safeners helped restore the biochemical homeostasis of the soil by preventing the inhibition of invertase and urease activities and increasing soil catalase activity. Furthermore, H1S2 promotion of dry matter accumulation, alleviation of herbicide inhibition on plant height, stem diameter, grainnumber per plant and thousand-grain weight resulted in a significant increase in grain yield (14.36 % in 2021 and 27.78 % in 2022) compared to other safener treatments. Overall, this study demonstrates that brassinolide as a safener can effectively mitigate the negative effects of herbicide on the growth and development of common buckwheat while also improving grain yield. These findings provide valuable technical guidance for sustainable and intensive production of common buckwheat in the Loess Plateau of Northwest China.

Temporal dynamics of total and bioavailable fungicide concentrations in soil and their effect upon nine soil microbial markers

Pesticides constitute an integral part of today's agriculture. Their widespread use leads to ubiquitous contamination of the environment, including soils. Soils are a precious resource providing vital functions to society - thus, it is of utmost importance to thoroughly assess the risk posed by widespread pesticide contamination. The exposure of non-target organisms to pesticides in soils is challenging to quantify since only a fraction of the total pesticide concentration is bioavailable. Here we measured and compared the bioavailable and total concentrations of three fungicides - boscalid, azoxystrobin, and epoxiconazole - and evaluated which concentration best predicts effects on nine microbial markers. The experiments were performed in three different soils at five time points over two months employing nearly 900 microcosms with a model plant. The total and bioavailable concentrations of azoxystrobin and boscalid decreased steadily during the trial to levels of 25 % and 8 % of the original concentration, respectively, while the concentration of epoxiconazole in soil nearly remained unchanged. The bioavailable fraction generally showed a slightly faster and more pronounced decline. The microbial markers varied in their sensitivity to the three fungicides. Specific microbial markers, such as arbuscular mycorrhizal fungi, and bacterial and archaeal ammonia oxidizers, were most sensitive to each of the fungicide treatments, making them suitable indicators for pesticide effects. Even though the responses were predominantly negative, they were also transient, and the impact was no longer evident after two months. Finally, the bioavailable fraction did not better predict the relationships between exposure and effect than the total concentration. This study demonstrates that key microbial groups are temporarily susceptible to a single fungicide application, pointing to the risk that repeated use of pesticides may disrupt vital soil functions such as nutrient cycling in agroecosystems.

The impact of agricultural management on soil aggregation and carbon storage is regulated by climatic thresholds across a 3000 km European gradient

Organic carbon and aggregate stability are key features of soil quality and are important to consider when evaluating the potential of agricultural soils as carbon sinks. However, we lack a comprehensive understanding of how soil organic carbon (SOC) and aggregate stability respond to agricultural management across wide environmental gradients. Here, we assessed the impact of climatic factors, soil properties and agricultural management (including land use, crop cover, crop diversity, organic fertilization, and management intensity) on SOC and the mean weight diameter of soil aggregates, commonly used as an indicator for soil aggregate stability, across a 3000 km European gradient. Soil aggregate stability (-56%) and SOC stocks (-35%) in the topsoil (20 cm) were lower in croplands compared with neighboring grassland sites (uncropped sites with perennial vegetation and little or no external inputs). Land use and aridity were strong drivers of soil aggregation explaining 33% and 20% of the variation, respectively. SOC stocks were best explained by calcium content (20% of explained variation) followed by aridity (15%) and mean annual temperature (10%). We also found a threshold-like pattern for SOC stocks and aggregate stability in response to aridity, with lower values at sites with higher aridity. The impact of crop management on aggregate stability and SOC stocks appeared to be regulated by these thresholds, with more pronounced positive effects of crop diversity and more severe negative effects of crop management intensity in nondryland compared with dryland regions. We link the higher sensitivity of SOC stocks and aggregate stability in nondryland regions to a higher climatic potential for aggregate-mediated SOC stabilization. The presented findings are relevant for improving predictions of management effects on soil structure and C storage and highlight the need for site-specific agri-environmental policies to improve soil quality and C sequestration.

Veterinary drug albendazole inhibits root colonization and symbiotic function of the arbuscular mycorrhizal fungus Rhizophagus irregularis

Arbuscular mycorrhizal fungi (AMF) are plant symbionts that have a pivotal role in maintaining soil fertility and nutrient cycling. However, these microsymbionts may be exposed to organic pollutants like pesticides or veterinary drugs known to occur in agricultural soils. Anthelminthics are veterinary drugs that reach soils through the application of contaminated manures in agricultural settings. Their presence might threaten the function of AMF, considered as sensitive indicators of the toxicity of agrochemicals to the soil microbiota. We determined the impact of the anthelminthic compounds albendazole and ivermectin on the establishment and functionality of the symbiosis between the model-legume Lotus japonicus and the AMF Rhizophagus irregularis. Our analyses revealed negative effects of albendazole on the development and functionality of arbuscules, the symbiotic organelle of AMF, at a concentration of 0.75 μg g-1. The impairment of the symbiotic function was verified by the reduced expression of genes SbtM1, PT4 and AMT2;2 involved in arbuscules formation, P and N uptake, and the lower phosphorus shoot content detected in the albendazole-treated plants. Our results provide first evidence for the toxicity of albendazole on the colonization capacity and function of R. irregularis at concentrations that may occur in agricultural soils systematically amended with drug-containing manures.

Organic Farming Allows Balanced Fungal and Oomycetes Communities

Conventional and organic farming systems affect soils differently, thereby influencing microbial diversity and composition. Organic farming, which relies on natural processes, biodiversity, and cycles adapted to local conditions, is generally known to improve soil texture and alleviate microbial diversity loss compared with that of conventional farming, which uses synthetic inputs such as chemical fertilisers, pesticides, and herbicides. Although they affect the health and productivity of host plants, the community dynamics of fungi and fungi-like oomycetes (under Chromista) in organic farmland are poorly understood. The present study aimed to determine the differences in the diversity and composition of fungi and oomycetes inhabiting organic and conventional farm soils using culture-based DNA barcoding and culture-independent environmental DNA (eDNA) metabarcoding. Four tomato farms with different farming practices were selected and investigated: mature pure organic (MPO) via non-pesticide and organic fertiliser, mature integrated organic (MIO) via non-pesticide and chemical fertiliser, mature conventional chemical (MCC) via both pesticide and chemical fertiliser, and young conventional chemical (YCC). Culture-based analysis revealed that different genera were dominant on the four farms: Linnemannia in MPO, Mucor in MIO, and Globisporangium in MCC and YCC. eDNA metabarcoding demonstrated that the fungal richness and diversity on the MPO farm were higher than that on other farms. Both conventional farms exhibited simpler fungal and oomycete network structures with lower phylogenetic diversity. Interestingly, a high richness of oomycetes was shown in YCC; in which, Globisporangium, a potential pathogenic group on tomato plants, was abundantly observed. Our findings indicate that organic farming enhances fungal and oomycete diversity, which may provide robust support for maintaining healthy and sustainable agricultural practices. This study contributes to our knowledge on the positive effects of organic farming on crop microbiomes and provides essential information for maintaining biological diversity.

Consequences of Arsenic Contamination on Plants and Mycoremediation-Mediated Arsenic Stress Tolerance for Sustainable Agriculture

Arsenic contamination in water and soil is becoming a severe problem. It is toxic to the environment and human health. It is usually found in small quantities in rock, soil, air, and water which increase due to natural and anthropogenic activities. Arsenic exposure leads to several diseases such as vascular disease, including stroke, ischemic heart disease, and peripheral vascular disease, and also increases the risk of liver, lungs, kidneys, and bladder tumors. Arsenic leads to oxidative stress that causes an imbalance in the redox system. Mycoremediation approaches can potentially reduce the As level near the contaminated sites and are procuring popularity as being eco-friendly and cost-effective. Many fungi have specific metal-binding metallothionein proteins, which are used for immobilizing the As concentration from the soil, thereby removing the accumulated As in crops. Some fungi also have other mechanisms to reduce the As contamination, such as biosynthesis of glutathione, cell surface precipitation, bioaugmentation, biostimulation, biosorption, bioaccumulation, biovolatilization, methylation, and chelation of As. Arsenic-resistant fungi and recombinant yeast have a significant potential for better elimination of As from contaminated areas. This review discusses the relationship between As exposure, oxidative stress, and signaling pathways. We also explain how to overcome the detrimental effects of As contamination through mycoremediation, unraveling the mechanism of As-induced toxicity.

Fungal bioassays for environmental monitoring

Environmental pollutants are today a major concern and an intensely discussed topic on the global agenda for sustainable development. They include a wide range of organic compounds, such as pharmaceutical waste, pesticides, plastics, and volatile organic compounds that can be found in air, soil, water bodies, sewage, and industrial wastewater. In addition to impacting fauna, flora, and fungi, skin absorption, inhalation, and ingestion of some pollutants can also negatively affect human health. Fungi play a crucial role in the decomposition and cycle of natural and synthetic substances. They exhibit a variety of growth, metabolic, morphological, and reproductive strategies and can be found in association with animals, plants, algae, and cyanobacteria. There are fungal strains that occur naturally in soil, sediment, and water that have inherent abilities to survive with contaminants, making the organism important for bioassay applications. In this context, we reviewed the applications of fungal-based bioassays as a versatile tool for environmental monitoring.

Prospective of mycorrhiza and Beauvaria bassiana silica nanoparticles on Gossypium hirsutum L. plants as biocontrol agent against cotton leafworm, Spodoptera littoralis

BACKGROUND

Plant-herbivorous insects are a severe danger to the world's agricultural production of various crops. Insecticides used indiscriminately resulted in habitat destruction due to their high toxicity, as well as disease resistance. In this respect, the development of a sustainable approach to supreme crop production with the least damage is a crucially prerequisite. As a result, the current study was carried out to understand the potential effect of arbuscular mycorrhizal (AM) fungi along with Beauvaria bassiana silica nanoparticles (Si NPs) as a new approach to increase cotton (Gossypium hirsutum L. Merr.) defense against an insect herbivore, Spodoptera littoralis. AM and non-AM cotton plants were infested with S. littoralis and then sprayed with a biopesticide [B. bassiana Si NPs] or a chemical insecticide (Chlorpyrifos).

RESULTS

The gas chromatography-mass spectrometry (GC-MS) analysis of B. bassiana Si NPs fungal extract showed that the major constituents identified were Oleyl alcohol, trifluoroacetate, 11-Dodecen-1-AL and 13-Octadecenal, (Z)-(CAS). Besides, results revealed a highly significant decrease in growth parameters in S. littoralis infested plants, however, with AM fungal inoculation a substantial improvement in growth traits and biochemical parameters such as protein and carbohydrates contents was observed. In addition, stimulation in proline and antioxidant enzymes activity and a decrease in malondialdehyde content were observed after AM inoculation.

CONCLUSION

AM fungi mitigate the harmful effects of herbivorous insects by strengthening the cotton plant's health via enhancing both morphological and biochemical traits that can partially or completely replace the application of chemical insecticides.

Arbuscular Mycorrhizal Fungi and the Need for a Meaningful Regulatory Plant Protection Product Testing Strategy

Arbuscular mycorrhizal fungi (AMF) perform key soil ecosystem services and, because of their symbiotic relationship with plant roots, may be exposed to the plant protection products (PPPs) applied to soils and crops. In 2017, the European Food Safety Authority (EFSA) released a scientific opinion addressing the state of the science on risk assessment of PPPs for in-soil organisms, recommending the inclusion of AMF ecotoxicological testing in the PPP regulatory process. However, it is not clear how this can be implemented in a tiered, robust, and ecologically relevant manner. Through a critical review of current literature, we examine the recommendations made within the EFSA report and the methodologies available to integrate AMF into the PPP risk assessment and provide perspective and commentary on their agronomic and ecological relevance. We conclude that considerable research questions remain to be addressed prior to the inclusion of AMF into the in-soil organism risk assessment, many of which stem from the unique challenges associated with including an obligate symbiont within the PPP risk assessment. Finally, we highlight critical knowledge gaps and the further research required to enable development of relevant, reliable, and robust scientific tests alongside pragmatic and scientifically sound guidance to ensure that any future risk-assessment paradigm is adequately protective of the ecosystem services it aims to preserve. Environ Toxicol Chem 2022;41:1808-1823. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Agricultural management and pesticide use reduce the functioning of beneficial plant symbionts

Phosphorus (P) acquisition is key for plant growth. Arbuscular mycorrhizal fungi (AMF) help plants acquire P from soil. Understanding which factors drive AMF-supported nutrient uptake is essential to develop more sustainable agroecosystems. Here we collected soils from 150 cereal fields and 60 non-cropped grassland sites across a 3,000 km trans-European gradient. In a greenhouse experiment, we tested the ability of AMF in these soils to forage for the radioisotope ³³P from a hyphal compartment. AMF communities in grassland soils were much more efficient in acquiring ³³P and transferred 64% more ³³P to plants compared with AMF in cropland soils. Fungicide application best explained hyphal ³³P transfer in cropland soils. The use of fungicides and subsequent decline in AMF richness in croplands reduced ³³P uptake by 43%. Our results suggest that land-use intensity and fungicide use are major deterrents to the functioning and natural nutrient uptake capacity of AMF in agroecosystems.

Chemical seed treatment and mycorrhizal inoculation provide better development and nutrition of common bean plants

BACKGROUND

Chemical seed treatment is an established practice in agriculture to protect crops from soil-borne pathogens and pests. Arbuscular mycorrhizal fungi (AMF) benefit plants by extending soil exploration as well as water and nutrient uptake. The objective of this work was to analyze the effects of combinations of seed treatments with doses of inoculant containing Rhizoglomus intraradices on vegetative development, root colonization and nutrition of Phaseolus vulgaris plants and soil microbiota.

RESULTS

Seed treatment benefited the vegetative development and nutrition of beans, with the treatments metalaxyl + fludioxonil + tiabendazole and pyraclostrobin + thiophanate methyl + fipronil standing out regarding the contents of nitrogen (N), phosphorus (P), iron (Fe) and zinc (Zn) of the aerial parts. Mycorrhizal inoculation linearly increased dehydrogenase activity, root biomass and total plant biomass, with increments reaching 27%. There was an interaction between seed treatment and inoculation dose for aboveground biomass and the contents of potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), manganese (Mn) and root colonization, with expressive results for the combination of the two highest doses of inoculant with metalaxyl + fludioxonil + tiabendazole or pyraclostrobin + methylthiophanate + fipronil in the seeds.

CONCLUSION

Chemical seed treatment and mycorrhizal inoculation benefited bean plants and their nutritional status. The best combinations for the bean crop were metalaxyl + fludioxonil + tiabendazole with 41.4 mg of the inoculant per 100 seeds and pyraclostrobin + thiophanate methyl + fipronil with 62.1 mg of the inoculant per 100 seeds. © 2022 Society of Chemical Industry.

Roles of Arbuscular mycorrhizal Fungi as a Biocontrol Agent in the Control of Plant Diseases

Arbuscularmycorrhizal fungi (AMF) are a class of beneficial microorganisms that are widely distributed in soil ecosystems and can form symbionts with 80% of terrestrial higher plants, and improve the nutritional status of plants. The use of AMF as a biocontrol method to antagonize soil-borne pathogens has received increasing interest from phytopathologists and ecologists. In this paper, the mechanisms of resistance to diseases induced by AMF and the application of AMF to plant fungal, bacterial, and nematode diseases have been summarized. This study aimed to enhance the potential use of AMF as a biological control method to prevent plant diseases in the future. Root morphological alteration characteristics were explained, including the influence of AMF on root structure, function, and the regulation of AMF via secondary metabolites. AMF can improve the rhizosphere environment by influencing the physical and chemical proprieties of soil, enhancing the growth of other beneficial microorganisms, and by competing with pathogenic microorganisms. Two microorganism types may compete for the same invasive sites in root systems and regulate nutrition distribution. AMF can induce the host plant to form defense systems, including improving phytohormone concentrations, inducing signal substrate production, gene expression regulation, and enhancing protein production.

Metabolic and antioxidant effects of inoculation with arbuscular mycorrhizal fungi in crops of flesh-coloured Solanum tuberosum treated with fungicides

BACKGROUND

Solanum tuberosum tubers have higher content of phenolic compounds such as hydroxycinnamic acid derivatives (HCAD) and anthocyanins in coloured genotypes. The use of fungicides for crops is common, but there are few studies regarding the interaction of fungicides and arbuscular mycorrhizal fungi (AMF). Here, the AMF-plant interactions and the metabolic responses of three potato genotypes with different tuber colorations (VR808, CB2011-509 and CB2011-104) inoculated with Claroideoglomus claroideum (CC), Claroideoglomus lamellosum (HMC26) or Funneliformis mosseae (HMC7) were studied together with the use of the fungicides MONCUT (M) and ReflectXtra (R). Mycorrhizal traits, phenolic compound profiles and antioxidant activity (AA) were evaluated.

RESULTS

Despite only two HCADs being identified, with 5-caffeolquinic acid the most abundant, four anthocyanins were detected only in purple potato genotypes. The anthocyanin and HCAD profiles, as well as AA, showed that the CB2011-104 genotype had better characteristics than the other genotypes, while VR808 and CB509 showed similar responses. The responses were dependent on the specific combinations of genotype, fungicide and the AMF strain, and generally showed better responses when colonized by AMFs.

CONCLUSION

The three potato genotypes had differential responses depending on the inoculated AMFs and the fungicide applied before sowing, where the optimal combinations for antioxidant response, mycorrhization degree and performance were HMC26/R for VR808, HMC7/M for CB2011-509 and HMC26/M for CB2011-104. Our results suggest the existence of functional compatibility that can be registered as beneficial effects even at the genotypic level of the host regarding a specific AMF strain. © 2021 Society of Chemical Industry.

Particularities of Fungicides and Factors Affecting Their Fate and Removal Efficacy: A Review

Systemic fungicide use has increased over the last decades, despite the susceptibility of resistance development and the side effects to human health and the environment. Although herbicides and insecticides are detected more frequently in environmental samples, there are many fungicides that have the ability to enter water bodies due to their physicochemical properties and their increasing use. Key factors affecting fungicide fate in the environment have been discussed, including the non-target effects of fungicides. For instance, fungicides are associated with the steep decline in bumblebee populations. Secondary actions of certain fungicides on plants have also been reported recently. In addition, the use of alternative eco-friendly disease management approaches has been described. Constructed Wetlands (CWs) comprise an environmentally friendly, low cost, and efficient fungicide remediation technique. Fungicide removal within CWs is dependent on plant uptake and metabolism, absorption in porous media and soil, hydrolysis, photodegradation, and biodegradation. Factors related to the efficacy of CWs on the removal of fungicides, such as the type of CW, plant species, and the physicochemical parameters of fungicides, are also discussed in this paper. There are low-environmental-risk fungicides, phytohormones and other compounds, which could improve the removal performance of CW vegetation. In addition, specific parameters such as the multiple modes of action of fungicides, side effects on substrate microbial communities and endophytes, and plant physiological response were also studied. Prospects and challenges for future research are suggested under the prism of reducing the risk related to fungicides and enhancing CW performance.

Roles of Arbuscular Mycorrhizal Fungi on Soil Fertility: Contribution in the Improvement of Physical, Chemical, and Biological Properties of the Soil

Many of the world's soils are experiencing degradation at an alarming rate. Climate change and some agricultural management practices, such as tillage and excessive use of chemicals, have all contributed to the degradation of soil fertility. Arbuscular Mycorrhizal Fungi (AMFs) contribute to the improvement of soil fertility. Here, a short review focusing on the role of AMF in improving soil fertility is presented. The aim of this review was to explore the role of AMF in improving the chemical, physical, and biological properties of the soil. We highlight some beneficial effects of AMF on soil carbon sequestration, nutrient contents, microbial activities, and soil structure. AMF has a positive impact on the soil by producing organic acids and glomalin, which protect from soil erosion, chelate heavy metals, improve carbon sequestration, and stabilize soil macro-aggregation. AMF also recruits bacteria that produce alkaline phosphatase, a mineralization soil enzyme associated with organic phosphorus availability. Moreover, AMFs influence the composition, diversity, and activity of microbial communities in the soil through mechanisms of antagonism or cooperation. All of these AMF activities contribute to improve soil fertility. Knowledge gaps are identified and discussed in the context of future research in this review. This will help us better understand AMF, stimulate further research, and help in sustaining the soil fertility.

Soil Microbiomes in Apple Orchards Are Influenced by the Type of Agricultural Management but Never Match the Complexity and Connectivity of a Semi-natural Benchmark

Conversion of natural ecosystems into agricultural land may strongly affect the soil microbiome and the functioning of the soil ecosystem. Alternative farming systems, such as organic farming, have therefore been advocated to reduce this impact, yet the outcomes of different agricultural management regimes often remain ambiguous and their evaluations mostly lack a proper more natural benchmark. We used high-throughput amplicon sequencing, linear models, redundancy analyses, and co-occurrence network analyses to investigate the effect of organic and integrated pest management (IPM) on soil fungal and bacterial communities in both the crop and drive rows of apple orchards in Belgium, and we included semi-natural grasslands as a benchmark. Fungi were strongly influenced by agricultural management, with lower diversity indices and distinct communities in IPM compared to organic orchards, whereas IPM orchards had a higher AMF abundance and the most complex and connected fungal communities. Bacterial diversity indices, community composition, and functional groups were less affected by management, with only a higher network connectivity and abundance of keystone taxa in organic drive rows. On the other hand, none of the agricultural soil microbiomes matched the complexity and connectedness of our semi-natural benchmark, demonstrating that even more nature-friendly agricultural management practices strongly affect the soil microbiome and highlighting the essential role of (semi-)natural systems as a harbor of robust and functionally diverse fungal and bacterial communities.

Effect of Inoculation with Arbuscular Mycorrhizal Fungi and Fungicide Application on the Secondary Metabolism of Solanum tuberosum Leaves

In potato (Solanum tuberosum) crops, the use of fungicides to control some diseases is widespread; however, it has been reported that this practice can modify the potato polyphenolic content, and new strategies oriented to the potato defense system are necessary. One alternative is the use of arbuscular mycorrhizal fungi (AMF) to improve the defense mechanisms of plants. In this study, phenolic profiles and antioxidant activities in leaves of three potato genotypes (CB2011-509, CB2011-104, and VR808) were evaluated in crops inoculated with three AMF strains (Claroideoglomus claroideum, Claroideoglomus lamellosum, and Fumneliformis mosseae) and with AMF in combination with the use of two commercial fungicides (MONCUT [M] and ReflectXtra [R]). Eight phenolic compounds were detected, mainly hydroxycinnamic acids (HCAD) and flavonols, in samples where the highest concentrations of HCAD were obtained, 5-caffeoylquinic acid was the most abundant phenolic. The antioxidant activity was higher using the cupric reducing antioxidant capacity (CUPRAC) and ferric reducing antioxidant power (FRAP) methods. The association of AMF with plants had benefits on the secondary metabolism; however, the response differed according to genotype. The different combinations of potato genotypes, AMF strain, and fungicide modified the content of phenolic compounds in leaves in different ways; the treatment using C. lamellosum and ReflectXtra was the ideal combination for the genotypes analyzed here, with the higher antioxidant response, which supports the further technological evaluation of efficient AMF strains and fungicides in potato crops.

Effects of Pesticides on the Diversity of Endophytic Fungi in Tea Plants

We examined the effects of agrochemicals on the endophytic fungal community associated with tea plants. Endophytic fungi were isolated from four different tea plant tissues (bark, xylem, old leaves, new leaves) collected from pesticide-treated and untreated plots. In pesticide-treated plot, the acaricides, fungicides, and insecticides are typically applied 3 times each year. The infection rate was slightly lower in the pesticide-treated plot, but the difference between plots was not statistically significant. Colletotrichum camelliae, Phyllosticta capitalensis, and Pleosporales sp. were common endophytes in both plots. Among a total of 41 fungal species, only 21 were considered common endophytes. Colletotrichum pseudomajus was the predominant endophyte in the bark tissue in the untreated plot, whereas C. camelliae was predominant in the pesticide-treated plot. Paraphaeosphaeria neglecta and Phoma bellendis were predominant in the xylem tissues of samples from the untreated and treated plots, respectively. Colletotrichum camelliae was the most commonly found species in leaf tissues in both plots, but the colonization frequency was significantly lower in the pesticide-treated plot. Species richness was not affected by pesticide treatment. The community structure of endophytic fungi in stem tissues (bark and xylem) differed significantly between plots, but leaf tissue endophytic fungal community structure was not significantly influenced by pesticide treatment.

Arbuscular mycorrhizal fungi improve uptake and control efficacy of carbosulfan on Spodoptera frugiperda in maize plants

BACKGROUND

Inoculation of arbuscular mycorrhizal (AM) fungi in soil can promote the uptake of nutrients and xenobiotics by plants. In this study, the effects of arbuscular mycorrhizal fungi (including Glomus intraradices and Glomus mossea) on the growth of maize, the uptake of carbosulfan and the control efficacy on Spodoptera frugiperda were investigated through maize seed coating.

RESULTS

Results from the pot experiment showed that carbofuran reduced the mycorrhizal colonization of AM fungi in the early stage of the experiment. The inhibiting effect disappeared in 21-49 DAP, whereas the mycorrhizal colonization rate under the G. intraradices treatment was maintained at ≈90%. Compared with noninoculated treatment, the fresh weights of roots in G. intraradices and G. mosseae treatments increased by 20-41% and 10-23%, respectively. Mycorrhizal treatment could significantly increase the transmission rates (root/soil and leaf/stem) and the carbosulfan accumulation in maize. During the harvest period, the control efficacy against S. frugiperda in mycorrhizal treatment was significantly higher than that in noninoculated treatments (P < 0.05) in both Guangzhou and Nanning.

CONCLUSIONS

Inoculation with AM could accelerate the degradation process of carbofuran in soil and the propagation of carbofuran from soil to plants. Glomus intraradices showed more pronounced effects than G. mosseae on both plant growth and carbosulfan content in plants and soil. The experimental results showed that inoculation of AM fungi increased the accumulation of carbofuran in plants, improved the effective utilization rate and enhanced the control efficacy against S. frugiperda. © 2021 Society of Chemical Industry.

Microbiota, pathogens, and parasites as mediators of tritrophic interactions between insect herbivores, plants, and pollinators

Insect-associated microbes, including pathogens, parasites, and symbionts, influence the interactions of herbivorous insects and pollinators with their host plants. Moreover, herbivory-induced changes in plant resource allocation and defensive chemistry can influence pollinator behavior. This suggests that the outcomes of interactions between herbivores, their microbes and host plants could have implications for pollinators. As epizootic diseases occur at high population densities, pathogen and parasite-mediated effects on plants could have landscape-level impacts on foraging pollinators. The goal of this minireview is to highlight the potential for an herbivore's multitrophic interactions to trigger plant-mediated effects on the immunity and health of pollinators. We highlight the importance of plant quality and gut microbiomes in bee health, and how caterpillars as model herbivores interact with pathogens, parasites, and symbionts to affect plant quality, which forms the centerpiece of multitrophic interactions between herbivores and pollinators. We also discuss the impacts of other herbivore-associated factors, such as agricultural inputs aimed at decreasing herbivorous pests, on pollinator microbiomes.

Fungicides With Contrasting Mode of Action Differentially Affect Hyphal Healing Mechanism in Gigaspora sp. and Rhizophagus irregularis

Fungicides are widely used in conventional agriculture to control fungal diseases, but may also affect non-target microorganisms such as arbuscular mycorrhizal (AM) fungi. These root symbionts develop extended mycelial networks within the soil via mechanisms such as anastomosis that indistinctly concerns intact and damaged hyphae, the latter being named hyphal healing mechanism (HHM). The HHM differs between Glomeraceae and Gigasporaceae. However, the effects of fungicides on this mechanism in unknown. Here, the impact of azoxystrobin, pencycuron, flutolanil, and fenpropimorph at 0.02 and 2 mg L-1 were tested in vitro on the HHM of Gigaspora sp. MUCL 52331 and Rhizophagus irregularis MUCL 41833, and repair events visualized carefully under a dissecting bright-field light microscope. Azoxystrobin was the more detrimental for both AM fungi at 2 mg L-1, while fenpropimorph impacted only R. irregularis (stimulating at low and inhibiting at high concentration). Conversely, flutolanil and pencycuron did not impact any of the two AM fungi. The mechanisms involved remains to be elucidated, but perturbation in the still-to-be firmly demonstrated spitzenkörper or in sterols content as well as a process of hormesis are possible avenues that deserve to be explored in view of a rationale management of chemicals to control fungal pathogens without harming the beneficial AM fungi.

Widespread Occurrence of Pesticides in Organically Managed Agricultural Soils-the Ghost of a Conventional Agricultural Past?

Pesticides are applied in large quantities to agroecosystems worldwide. To date, few studies assessed the occurrence of pesticides in organically managed agricultural soils, and it is unresolved whether these pesticide residues affect soil life. We screened 100 fields under organic and conventional management with an analytical method containing 46 pesticides (16 herbicides, 8 herbicide transformation products, 17 fungicides, seven insecticides). Pesticides were found in all sites, including 40 organic fields. The number of pesticide residues was two times and the concentration nine times higher in conventional compared to organic fields. Pesticide number and concentrations significantly decreased with the duration of organic management. Even after 20 years of organic agriculture, up to 16 different pesticide residues were present. Microbial biomass and specifically the abundance of arbuscular mycorrhizal fungi, a widespread group of beneficial plant symbionts, were significantly negatively linked to the amount of pesticide residues in soil. This indicates that pesticide residues, in addition to abiotic factors such as pH, are a key factor determining microbial soil life in agroecosystems. This comprehensive study demonstrates that pesticides are a hidden reality in agricultural soils, and our results suggest that they have harmful effects on beneficial soil life.

Ecotoxicological test to assess effects of herbicides on spore germination of Rhizophagus clarus and Gigaspora albida

Given the essential role of arbuscular mycorrhizal fungi (AMF) in soil systems and agriculture, their use as biological indicators has risen in all fields of microbiology research. However, AMF sensitivity to chemical pesticides is poorly understood in field conditions, and not explored in ecotoxicology protocols. Hence, the goal of this study was to evaluate the effects of different concentrations of glyphosate (Roundup®) and diuron+paraquat (Gramocil®) on the germination of spores of Gigaspora albida and Rhizophagus clarus in a tropical artificial soil. This study was conducted in 2019 at the Soil Ecology and Ecotoxicology Laboratory of the Universidade do Estado de Santa Catarina. The nominal concentrations of glyphosate were 0, 10, 50, 100, 250, 500, 750 and 1000 mg a.i. kg-1. For diuron+paraquat, the concentrations tested were 0, 10 + 20, 50 + 100, 100 + 200, 250 + 500, 500 + 1000, 750 + 1500 and 1000 + 2000 mg a.i. kg-1. Glyphosate did not alter germination of G. albida, but germination inhibition of R. clarus spores was of 30.8% at 1000 mg kg-1. Diuron+paraquat inhibited by 8.0% germination of G. albida, but only at the highest concentration tested. On the other hand, effects on R. clarus were detected at 50 + 100 mg kg-1 concentration and above, and inhibition was as high as 57.7% at the highest concentration evaluated. These results suggest distinct response mechanisms of Rhizophagus and Gigaspora when exposed to herbicides, with the former being more sensitive than the later.

Mycorrhizal Interventions for Sustainable Potato Production in Africa

The potato (Solanum tuberosum L.) is an important tuber crop with high dietary value that could potentially help to alleviate malnutrition and hunger in Africa. However, production is expensive, with high fertilizer and pesticide demands that lead to environmental pollution, and tillage practices that negatively affect soil structure. Microorganisms of different types have increasingly been found to be useful as biofertilizers, and arbuscular mycorrhizal (AM) fungi are an important crop symbiont. AM fungi have been shown to increase tolerance of crop plants to drought, salinity and disease by facilitating water and nutrient acquisition and by improving overall soil structure. However, the establishment and maintenance of the symbioses are greatly affected by agricultural practices. Here, we review the benefits that AM fungi confer in potato production, discuss the role and importance of mycorrhiza helper bacteria, and focus on how AM fungal diversity and abundance can be affected by conventional agricultural practices, such as those used in potato production. We suggest approaches for maintaining AM fungal abundance in potato production by highlighting the potential of conservation tillage practices augmented with cover crops and crop rotations. An approach that balances weed control, nutrient provision, and AM fungal helper bacterial populations, whilst promoting functional AM fungal populations for varying potato genotypes, will stimulate efficient mycorrhizal interventions.

Arbuscular Mycorrhizal Fungi and Associated Microbiota as Plant Biostimulants: Research Strategies for the Selection of the Best Performing Inocula

Arbuscular mycorrhizal fungi (AMF) are beneficial soil microorganisms establishing mutualistic symbioses with the roots of the most important food crops and playing key roles in the maintenance of long-term soil fertility and health. The great inter- and intra-specific AMF diversity can be fully exploited by selecting AMF inocula on the basis of their colonization ability and efficiency, which are affected by fungal and plant genotypes and diverse environmental variables. The multiple services provided by AMF are the result of the synergistic activities of the bacterial communities living in the mycorrhizosphere, encompassing nitrogen fixation, P solubilization, and the production of phytohormones, siderophores, and antibiotics. The tripartite association among host plants, mycorrhizal symbionts, and associated bacteria show beneficial emerging properties which could be efficiently exploited in sustainable agriculture. Further in-depth studies, both in microcosms and in the field, performed on different AMF species and isolates, should evaluate their colonization ability, efficiency, and resilience. Transcriptomic studies can reveal the expression levels of nutrient transporter genes in fungal absorbing hyphae in the presence of selected bacterial strains. Eventually, newly designed multifunctional microbial consortia can be utilized as biofertilizers and biostimulants in sustainable and innovative production systems.

Two herbicides, two fungicides and spore-associated bacteria affect Funneliformis mosseae extraradical mycelium structural traits and viability

The extraradical mycelium (ERM) produced by arbuscular mycorrhizal fungi is fundamental for the maintenance of biological fertility in agricultural soils, representing an important inoculum source, together with spores and mycorrhizal root fragments. Its viability and structural traits, such as density, extent and interconnectedness, which are positively correlated with the growth and nutrition of host plants, may be affected by different agronomic practices, including the use of pesticides and by different mycorrhizospheric communities. This work, carried out using a whole-plant experimental model system, showed that structural traits of ERM, such as length and density, were strongly decreased by the herbicides dicamba and glufosinolate and the fungicides benomyl and fenhexamid, while anastomosis frequency and hyphal branching were differentially modulated by singly inoculated mycorrhizospheric bacteria, depending on their identity.

Impact of Ridomil, Bavistin and Agrothoate on arbuscular mycorrhizal fungal colonization, biochemical changes and potassium content of cucumber plants

The effect of pesticides on arbuscular mycorrhizal (AM) fungi and plants are of interest to agriculture. Hence, the present study was conducted to understand the potential effect of two systemic fungicides (Ridomil "250 and 500 mg/L" and Bavistin "500 and 1000 mg/L") and one insecticide (Agrothoate 40% EC "1.25 and 2.50 ml/L H₂O") on AM fungal colonization, some biochemical changes and K⁺ content of cucumber plants (Cucumis sativus L.). AM and non-AM cucumber plants were exposed to two concentrations of each pesticide. Results revealed an increase in mycorrhizal colonization (F%) with Ridomil and Bavistin applications however there was a decrease in this percentage with Agrothoate. Stimulation of phosphatase enzymes activity was observed subsequent to pesticides application. Moreover, there was a significant decrease in K⁺ content with increasing pesticides concentration, and this decrease was more distinct in non-AM cucumber plants than AM ones. Our results also showed a significant increase in malondialdehyde (MDA) content in all pesticides treated cucumber plants relative to control ones. Thus, the content of non-enzymatic antioxidants such as phenolic and flavonoids was stimulated by pesticides application and with AM fungal inoculation, further augmentation in their contents was detected. Therefore AM fungi can partially or completely alleviate pesticides toxicity and helpful to overcome some of their negative effects on the biochemical metabolites of cucumber. Thus the judicious use of these pesticides may have stimulatory effect on AM fungal colonization.