Effects Of Pesticides On The Environment And Human Health – In recent years, the spread and implementation of next-generation sequencing and the reduction of costs has sparked interest in phytobiome studies that allow dissection of the ecological interactions that regulate the holobiont. Indeed, crop plants are associated with a wide diversity of microorganisms in all their parts. Crop microbiota influence plant phenotype, growth, yield and quality contributing to plant resistance to disease, plant adaptation to abiotic stresses and plant nutrition. The association between land plants and microbes developed at least 460 million years ago, as suggested by fossil evidence of the first land plants, indicating the essential role of microbes for plants. Recent studies indicate that plants actively recruit beneficial microorganisms to facilitate their adaptation to environmental conditions. Cultivation methods and disease control measures can affect the structure and functions of the plant microbiome. The applications of pesticides and biological control agents can alter the biodiversity in the phytobiota and suppress the beneficial functions. However, to date, the effects of disease control measures on phytobiota and their possible side consequences on plant growth, productivity and crop quality remain a neglected field of study . The present work summarizes the known effects on the phytobiota providing evidence on the role of the plant microbial community in determining the overall effectiveness of the control measure applied and suggests that future studies on the control of plant diseases also consider microbe-mediated effects on plant fitness.
Plants live in close association with a dynamic phytobiota, consisting of a macrobiota and also a microbiota, especially the microbes that inhabit the soil in which the plants grow. The importance of soil microbial communities is well recognized for their role in plant performance, including the improvement of plant growth, vigor and fitness traits (Marschner and Rumberger, 2004; Lau and Lennon, 2011; Chaney and Baucom, 2020). the acquisition of nutrients (Chaparro et al., 2012; Reverchon et al., 2015), associated with the presence of rare taxa (Hol et al., 2010), and the attraction of pollinators, predators and parasites of herbivores (Wagner et al., 2010). , 2014; Berg et al., 2016; Etemadi et al., 2018). Plants modulate the microbiota of the rhizosphere (Berendsen et al., 2012; Kwak et al., 2018) and selectively recruit beneficial microbes (Park and Ryu, 2021) thanks to signals, including root exudates, volatile compounds ( VOCs) and phytohormones, which help shape the phytobiota by recruiting, repelling and coordinating interactions (Dicke, 2016). Microorganisms associated with plants form complex networks with other members of the same species and also with different species, genera, families and even domains of life (Wassermann et al., 2019a). Cooperation between plants and microorganisms, as well as intra-microbiome interactions, require intense communication that regulates community assembly (Agler et al., 2016; Venturi and Keel, 2016).
Effects Of Pesticides On The Environment And Human Health
The homeostatic balance between microbe-microbe and host-microbe interactions is critical to plant health. Disturbance of this balance is often referred to as microbial dysbiosis and may represent an important disease mechanism (Martins dos Santos et al., 2010; Sekirov et al., 2010; Kemen, 2014). For example, under high humidity conditions, several immunocompromised mutants of Arabidopsis show damage to leaf tissues linked to an altered composition of the phyllosphere microbiota, somewhat similar to the dysbiosis found in human inflammatory bowel disease (Chen et al., 2020). Importantly, bacterial community transplantation experiments showed that the application of a dysbiotic leaf bacterial community to healthy plants causes tissue damage, demonstrating that, in this case, dysbiosis is the cause of the observed symptomatology (Chen et al. , 2020). However, it is worth noting that stress-induced deviation from eubiosis is not always associated with reduced plant performance (Paasch and He, 2021).
How Toxic Is The World’s Most Popular Herbicide Roundup?
Phytobiota protect crops from diseases through different modes of action: i) indirect effects mediated by the activation of plant-induced systemic resistance (ISR), an early resistance to root-borne pathogen infections to plant tissues (Pieterse et al., 2014; Conrath). et al., 2015), ii) niche exclusion of pathogens from competition for nutrients and space (Spadaro and Droby, 2016), and/or iii) direct interaction with pathogens through hyperparasitism (invasion and killing of mycelium, spores and resting structures) or antibiosis (production of antimicrobial secondary metabolites) (Raaijmakers and Mazzola, 2012; Ghorbanpour et al., 2018). Finally, some fungal viruses are used to induce hypovirulence (Milgroom and Cortesi, 2004; Double et al., 2018) and microbial antagonists can act through the inactivation of enzymes involved in pathogenic infections (Elad, 2000) or the enzymatic degradation of pathogenic structures. (Köhl et al., 2019).
An easily overlooked, but also intrinsically important, aspect to consider when studying phytobiota is that pathogenic species are themselves part of the entire microbiota (Kamada et al., 2013). This is indeed a core aspect of epidemiology since the presence of a pathogen does not necessarily lead to infection and disease is only caused under specific inductive conditions (Scholthof, 2007). In the context of dysbiosis, the concept of pathobiota, which integrates pathogens in biotic environments, has been established and applied to many pathosystems (Baltrus, 2017). Analyzes of the pathobiota often reveal that pathogens do not operate independently, and several pathogens could be involved in severe dysbiosis (Singer, 2010; Lamichhane and Venturi, 2015; Berg et al., 2021). This is the case of Fusarium Head Blight, a highly dynamic disease caused by a complex of different Fusarium species, whose composition is geographically dependent, and each of them can respond differently to the changing climate (Yli-Mattila, 2010; Vaughan et al., 2016). Although predominant, the highly virulent F. graminearum is only one member of the species complex (Ioos et al., 2005; Xu et al., 2005) and it has recently been established that strategies the fight against F. graminearum is hindered by the presence of the weakly pathogenic F. poae, which shows the complexity of developing control strategies against plant diseases caused by several pathogens (Tan et al., 2021). A similar scenario was observed for phytopathogenic bacteria. Pseudomonas syringae pv. actinidiae is always present in syndemic association with Pseudomonas syringae pv. syringae and Pseudomonas viridiflava, two other pathogens of kiwifruit, suggesting the establishment of a pathogenic consortium leading to greater pathogenic capacity (Purahong et al., 2018). For these reasons, new disease control strategies should target the entire phytobiota and possible pathogen consortia within it rather than single pathogens to develop suppressive microbial communities capable of restricting multiple pathogens at the same time.
Our current understanding of communications in phytobiota is still largely based on interactions involving two or three components, and is often measured under controlled conditions. However, another level of complexity in the study of phytobiota is related to the eukaryotic organisms that interact with plants, each of them harboring its own internal and external microbiota, influencing the interaction between plants and their communities microbes (Cusano et al., 2011; Khaitov et al., 2015). The intense communication between members of the plant holobiont and the observations that signals can be co-opted, modified, or even destroyed, by another member of the community reinforce the need for a systems-level analysis of the communication mechanisms to exploit phytobiota manipulation for crop improvement. Figure 1).
Figure 1 The role of phytobiota and the effects of disease control measures on phytobiota (current situation). The panel on future development will highlight various strategies to achieve a durable and sustainable disease control approach based on phytobiota manipulation.
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Chemical pesticides are widely used in intensive agriculture and are still the most effective, reliable and economical tool to minimize losses caused by pests and diseases (Huang et al., 2021a). In this view, pesticides and fertilizers are essential to ensure food security for the ever-growing world population. Globally, more than 2 million tons of pesticides are used annually (Sharma et al., 2019). In Europe, awareness of the risks of pesticides has led to the development of policies for their sustainable use (Directive 2009/128/EC) and actions, such as the Farm2ForK Strategy, which aims to reduce the 50 % of pesticide use in 2030. Indeed, in the last decade, the use of pesticides in the EU has been reduced by 10.2% with the lowest total volume (333, 500 tons) of sales registered in 2019. Fungicides, bactericides and herbicides are still the major groups of pesticides currently used (EUROSTAT). – European Statistics, 2021). The increasing concern about the effect of pesticides on human and environmental health has stimulated research on sustainable alternatives, as well as the extensive study of the direct and indirect effects of their use on non-target organisms and the ecosystem services they provide (Ramakrishna). et al., 2019). Soil microbiota is crucial for ecosystem functions (Karas et al., 2018). Since synthetic fertilizers and pesticides have a long persistence in the soil, in the last decade, many studies have investigated the effect of pesticides and fertilizers on soil microflora and microbial fertility, which have a direct impact on to environmental quality and plant health and productivity (Hartmann). et al., 2014; Zhu et al., 2016; Huang et al., 2021b). This led the European Food Safety Authority (EFSA) to include soil microorganisms in the environmental risk assessment of pesticides (EFSA Panel on Plant Protection Products and their Residues (PPR), 2010; Karas et al., 2018). However, the evaluation of the toxicology of pesticides is based only on their impact on the N mineralization test (OECD, 2000) and therefore does not provide information on the key functions of the soil microbiota (Karas et al., 2018). Despite the growing body of knowledge on the impact of pesticides on soil microorganisms, standardized methods have not been developed and most studies have been conducted at a laboratory scale or with exposure levels higher.
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