Soil is a reservoir of millions of microorganisms which imparts great impact on agriculture. A majority of microbes are beneficial for soil and plant health. However, some microorganisms pose great threat to crops as they often damage the root and crown tissues of plants thereby causing huge economic loses. Thus, pathogens which persist in the soil matrix or in residues over the soil surface are known as soil-borne plant pathogens (Veena et al., 2014). The soil-borne plant pathogens are distributed widely in soil however, few species exhibit localized distribution pattern. Soil-borne diseases caused by fungi, bacteria, nematodes, oomycetes, protozoa, viruses are considered vital in realization of potential yield in agricultural crops. Once established, these pathogens accumulate through synergistic associations and cause greater economic losses that are difficult to control. The soil-borne plant pathogens viz., Fusarium spp., Rhizoctonia spp., Pythium spp., Sclerotinia spp., Verticillium spp., and Phytophthora spp. can cause yield loss upto 50-75% for economically important crops such as wheat, maize, cotton, vegetables and fruits (Mihajlovic et al., 2017). Fusarium oxysporum strains alone can infect more than 150 agricultural crop species such as banana, tomato, melon, cotton etc. causing severe vascular wilt disease (Bertoldo et al., 2014). In cucurbitaceous crops, the pathogen is responsible for causing yield losses of around 30-80% (Lü et al., 2011). Fusarium wilt of banana, caused by F. oxysporum f. sp. cubense is a major threat to banana cultivation worldwide. The race Tropical Race 4 has been causing serious losses in Southeast Asian countries, thereby affecting the lives of small producers. Asides from wilt disease, some other strains of Fusarium oxysporum are capable of causing root/foot rot and damping off (Michielse and Rep, 2009). F. solani is mainly known to cause collar and root rots in many economically important crops such as beans and peas. Fusarium spp. also contaminate cereals and food grains by producing mycotoxins such as fumonisins, trichothecenes, zearalenone, and deoxynivalenol (Nelson et al., 1981). F. graminearum and F. verticillioides cause cob rot in maize, both species are known to produce mycotoxins. In oil seed rape (Brassica napus), the predominant population of Rhizoctonia solani AG2-1 isolate causes severe seedling diseases, establishment losses of up to 80-100%, and final yield losses of up to 30%. (Tahvonen et al., 1984; Kataria and Verma, 1992; Khangura et al., 1999). Rhizoctonia produces a variety of symptoms such as stem lesions, damping off, crown rot, root rot, stem rot and aerial web blight. The infection ultimately causes wilting, stunting and finally the death of the plant. The species of Phytophthora and Pythium cause damping off and root rot disease under cool and wet conditions and can affect 5-80% of the seedlings thereby incurring huge economic loss to the farmers (Alcala et al., 2016). Late blight caused by Phytophthora spp. is one of the most destructive soil-borne diseases of potatoes and tomatoes worldwide (Son et al., 2008). Worldwide, it causes an estimated loss of $5 billion annually (Latijnhouwers et al., 2004). Among the bacterial soil-borne pathogens, Ralstonia solanacearum causing bacterial wilt disease in more than 180 plants of 45 families ranks the first (Tahat and Sijam, 2010). In tomato crop, R. solanacearum can cause yield loss of 0-90% depending on the strain of the pathogen, cropping pattern, cultivar and climate (Nion and Toyota, 2015). Root knot nematodes (RKN) represent an important class of soil-borne pathogen that infect more than 5,500 host plants. Meloidogyne spp. are polyphagous, obligate sedentary, parthenogenetic and considered the most important plant parasitic nematode group worldwide (Jones et al., 2013). The typical symptoms produced by RKN include gall formation and damage to root system, along with above ground symptoms such as chlorosis, stunting, wilting and yield reduction (Karssen et al., 2013). The effect of RKN on the host plant is further intensified by the attack of secondary plant pathogens such root rot, fungal and bacterial wilt causing pathogens (Back et al., 2002; Karssen et al., 2013). The soil-borne diseases remain unnoticed until the above ground plant parts exhibit symptoms such as chlorosis, stunting, wilting and finally death. The common soil-borne diseases include damping off, root rot, vascular wilt etc. (Hornby et al., 1988). These diseases are often difficult to manage as they have wide host range and can survive for long periods on soil organic matter and plant debris, as free-living organisms or by producing resistant structures like sclerotia, microsclerotia, oospores or chlamydospore even in absence of host plant. Also, its diagnosis is difficult and cumbersome due to similarity in symptoms such as root rot, stunting, chlorosis, seedling damping, root blackening, bark cracking and branch and twig dieback (Patil et al., 2021). The non-specific symptoms and its resemblance with physiological disorders and water stress symptoms makes its timely diagnosis difficult (Åström and Gerhardson, 1988). Thus, the major hinderance in management of soil-borne diseases is its heterogenous incidence and scarce knowledge on the epidemiological aspects of pathogens. The experiences and observations passed on through several generations have given rise to cultural practices that reduce the losses caused by soil-borne plant pathogens but its effective management strategy still need to be explored. The expanding diversity of crops in agriculture emphasizes parallel expansion of strategies and develop novel strategies for effective management of soil-borne plant pathogens.

The farmers use synthetic fumigants and chemical fungicides at regular interval throughout the cropping season to minimize the soil-borne disease outbreak. However, extensive use of fumigants such as methyl bromide and fungicides disrupt the ecological balance, cause human and animal health hazards, damage to aquatic ecosystem and beneficial organisms in soil (Panth et al., 2020). The cultural practices such as crop rotation, biofumigation, anaerobic soil disinfestation, soil solarization, soil steam sterilization are mainly adopted by farmers to minimize the losses but these methods give inconsistent results and are less effective than chemical control methods. The mounting environmental constraints and ineffective management options emphasizes need of alternative sustainable and effective management strategy.

Nanotechnology emerged as one of the most rapidly advancing science of twenty first century. Diversified application of nanotechnology in various fields have been found to uplift the entire scenario of industry and agricultural sector including information technology, medicine, disease detection and diagnosis, food safety and security, pest and disease management, environmental science and many more. From agriculture point of view, the major concern related to soil and environmental health includes: increased pesticide residue in soil and water bodies, decline in soil beneficial organisms, alteration of soil physical and chemical properties, pesticide resistance in pathogens and many more (Sharma et al., 2019). Nanotechnology can address most of these concerns and can bring revolutionary changes. It possesses marvelous application as antimicrobial and therapeutic compounds, targeted drug delivery, high sensitivity disease detection and diagnosis and thus likely to enhance agricultural productivity due to decline in cost associated with agricultural production practices (Dutta et al., 2021; Dutta et al., 2022). The small size of nanoparticles (<100 nm), greater surface area to volume ratio and high reactivity favors its wide-scale application in the field of human and plant pathology (Jeevanandam et al., 2018). The use of nano-encapsulated fertilizers and pesticides can reduce the amount of chemical fumigants and pesticides reaching the soil surface as compared to conventional formulations and also prolongs protection to plants against various phytopathogens. Nano-based materials can also act as cargo molecule and can release the active ingredients owing to its greater surface area to volume ratio. The effect on non-target organisms can also be reduced as they are highly target specific (Din et al., 2017). The disease tolerance ability of plants can also be enhanced thereby improving plant health ( Figure 1 ). Thus, it may be predicted that integrity between timely and accurate disease diagnosis and management can be established in near future by exploiting the science of nanotechnology (Mahmood et al., 2017). Recent studies have revealed that nanoparticles show promising results as potential antimicrobial agent and biosensor for detection of plant pathogens especially against soil-borne plant pathogens. This review, focuses on all aspects of nanotechnology for management of soil-borne plant pathogens, thereby condensing scattered literature together at one place.

In the field of agriculture, nanoscience is explored in delivery of plant hormones, seed germination, transfer of genes of interest, water management, nano-biosensors, nanobarcoding and controlled release of agro-chemicals (Hayles et al., 2017). Furthermore, nanoparticles are engineered with desired properties (i.e., size, shape, surface area etc.) for its use as protectant, therapeutant or site specific delivery of active ingredients such as fungicides via conjugation, adsorption or encapsulation (Khandelwal et al., 2016). The nano-based materials can be applied to plants as seed treatment, root dip treatment, soil application and foliar spray. The metallic oxides, nonmetals, metalloids, polymeric and carbon nanomaterials exhibit disease suppressing and growth promoting activities in plants (Elmer et al., 2018). The most popularly explored nanoparticles include silver, gold, copper, zinc oxide, iron and many more. The three main mechanisms involved in use of nanoparticles include: (a) nanoparticle as biosensor, (b) nanoparticle as protectant or therapeutant, and (c) nanoparticle as smart delivery vehicle of fungicides or actives such as target genes. Nanoparticles such as quantum dots and metallic nanoparticles can be functionalized with biological markers for in situ and rapid detection of soil-borne pathogens. The nanoparticles have the potential to serve as protective or therapeutic agents against a variety of soil-borne pathogens, viz., Fusarium oxysporum, Sclerotium rolfsii, Rhizoctonia solani, Sclerotinia sclerotiorum (Kaman and Dutta, 2019; Abdelrhim et al., 2021) Ralstonia solanacearum (Khairy et al., 2022), soil-borne viruses viz., Barley yellow mosaic virus (BaYMV) (Aref et al., 2012), etc. The main mechanism of action against microorganisms include agglutination and cell membrane disruption, inhibition of synthesis of RNA, proteins, toxins, enzymes such as H+-ATPase and blockage of flow of nutrients (Dakal et al., 2016; Malerba and Cerana, 2016). Nanoparticles also acts as carrier molecule and allow target-specific release of active ingredients into the plant system, thereby reducing the load of chemicals into the environment. The nano-based formulations provide several benefits such as improved water solubility of pesticides, site specific delivery and uptake by target sites, increased shelf life, reduced effect on non-target organisms and residual effect on environment (Hayles et al., 2017). Also, the stability and activity of nano-based formulations are greater as compared to conventional pesticides even under unfavorable environmental conditions (rainfall and UV exposure), thereby reducing the number of applications, toxicity and overall costs.

Another important aspect of plant health management is the use of fertilizers. Nanofertilizers bear the potential to increase the release and uptake efficacy of nutrients thereby boosting plant disease resistance. It has widely been explored in plant/disease systems viz., Fusarium wilt in tomato, chrysanthemum, root and crown rot in asparagus, red root rot in tea, verticillium wilt in brinjal (Elmer et al., 2018).

Rapid detection and diagnosis of soil-borne pathogens is fundamental for its effective and timely management. A number of immunological, serological, nucleic acid-based detection assays have been developed for accurate detection of plant pathogens. Over the past two decades, numerous efforts have been made to develop methods for diagnosing and monitoring plant infections using biochemical assays utilizing specific proteins, toxins, ELISA, nucleic acid probe technologies, and PCR amplification of nucleic acid sequences (McCartney et al., 2003; Sundelin et al., 2009; Kashyap et al., 2013a; Kumar et al., 2013; Kumar and Kashyap, 2013; Singh et al., 2014). These biochemical assays and nucleic acid-based methods are sensitive, exact, and useful for verifying visual scouting, but they are unsuitable as screening tests to check on the health of plants before symptoms manifest. They necessitate intricate sampling techniques, costly infrastructure, and might mask the true state of pathogen infections. Unfortunately, only a small number of plant diseases can be effectively detected using these assays. However, the majority of these techniques are ineffective for on-site disease detection in crop fields. The use of molecular approaches is further constrained by the high cost and limited shelf life of molecular biology reagents like enzymes and primers. Therefore, the introduction of low-cost techniques to increase the precision and speed of plant pathogen diagnostics is required.

Recent advancement in nanotechnology has led to development of functional nanoparticles (electronic, optical, magnetic, or structural) which can be covalently attached to biological molecules including nucleic acids, peptides and proteins. Quantum dots (QD), one of the most promising nanomaterials, have been extensively exploited in a wide range of bio-related applications, including the quick and precise detection of a specific biological marker (Kashyap et al., 2015).Tools for high-throughput analysis, high-quality monitoring, and crop protection such as biosensors, quantum dots, nanostructured platforms, nanoimaging, and nanopore DNA sequencing have the potential to increase the sensitivity, specificity, and speed of disease detection (Khiyami et al., 2014). Additionally, nano-diagnostic kit tools are rapid and simple to use in identifying potential plant pathogens, enabling specialists to assist farmers in the prevention of epidemic illness. The ability of QD-based nanosensors to simultaneously probe several enzyme activities has been demonstrated by Knudsen et al. (2013). CdTe quantum dots have been utilized as biosensors by coating with specific antibodies against the glutathione S-transferase (GST) protein of Polymyxa betae, the vector of BNYVV causing rhizomania disease in sugar beet (Safarpour et al., 2012). In order to detect the harmful fungus Sclerotinia sclerotiorum, Wang et al. (2010) used indirect stimulation to construct a sensitive electrochemical sensor employing a modified gold electrode with copper nanoparticles. They used this sensor to successfully and precisely quantify salicylic acid in oilseeds to detect the pathogen. It is necessary to conduct more research on related sensors and sensing systems to detect pathogens, their byproducts, or to track physiological changes brought on by infections in plants. Schwenkbier et al. (2015) created a helicase-dependent isothermal amplification (HDA) in conjunction with on-chip hybridization for identifying Phytophthora species. With this method, the target gene locus for the yeast GTP-binding protein (Ypt1) can be amplified effectively at a single consistent temperature in a tiny heating unit. By using on-chip DNA hybridization and subsequent silver nanoparticle deposition, the assay’s specificity was established. The silver deposits act as reliable endpoint signals, enabling both electrical and optical readout. These developments suggest that the combined techniques will soon be applied on-site for the accurate identification of several soil-borne pathogens. Hervas et al. (2011) established a “lab-on-chip” method for the rapid, sensitive, and selective quantification of zearalenone generated by Fusarium sp. that incorporates an electrokinetic magnetic bead-based electrochemical immunoassay on a microfluidic chip. Rispail et al. (2014) studied the effects of superparamagnetic nanoparticles and quantum dots on Fusarium oxysporum. The presence of the pathogenic fungus was quickly identified by interactions between nanomaterials and the fungal hypha, though their internalization patterns varied. This study showed viability of new nanotechnology-based systems for the early detection and eventual control of harmful fungi which is the first study on the effects of quantum dots and superparamagnetic particles on fungal cells. Hashimoto et al. (2008) created a novel biosensor system comprising two biosensors for rapid detection of soil-borne pathogens. Here, equal amounts of two distinct microorganisms, each immobilized on an electrode, were used to build the system.

However, the science of nanodiagnostics is still in the toddler stage for accurate detection of pathogens and toxins in agricultural field. Extensive research is needed to optimize the diagnostic assays for detection of precise signals emitted from low level of pathogens. Also, efforts must be channelized towards development of portable, cheap, efficient and hand held nanodevices for in situ detection of soil borne pathogens.

Soil borne plant pathogens represent diverse group of microorganisms such as fungi, bacteria, viruses, nematodes dwelling in soil and cause huge economic loss by affecting the root and collar region of plants. These pathogens are difficult to manage using conventional strategies as chemical pesticides can hardly reach into the soil system and large amount of these chemicals upsets the soil and environmental health. Nanotechnology has emerged as one of the potential management strategy to curb the menace of soil-borne plant pathogens. Nanomaterials can be effectively utilized to manage soil-borne pathogens owing to their versatile antimicrobial properties, including generation of ROS, cell membrane, organelles and other macromolecule destabilization and toxicity due to nanoparticles. The smaller size and greater surface area to volume ratio of nanoparticles allow for greater penetration potential and better interaction with soil-dwelling microbes thereby increasing their control efficacy. Nanomaterials can also be used as smart delivery vehicle for pesticides, fungicides and fertilizers to reduce the chemical load on the environment. Also, nanodiagnostics have emerged as a potential science to overcome the difficulties associated with the detection of soil-borne pathogens. Nanotechnology have been utilized to develop affordable biosensor systems for the early and sensitive detection of soil-borne pathogens based on the qualitative and quantitative detection of specific metabolites secreted by them. The indirect mechanism of management of soil-borne pathogens involves activation of plant defense mechanism and promotion of plant growth. To use nanomaterials wisely in soil-borne pathogen protection, it is imperative to understand their ecotoxicity, phytotoxicity, cytotoxicity, genotoxicity and interactions with the soil system and the soil residents. The nanomaterials upon reaching the soil, directly interact with soil particles affecting physicochemical properties, fertility and beneficial organisms. The effect of nanoparticles on soil structure, soil functioning, organic matter, siderophore production, nitrogen fixation, phosphate and potassium solubilization, and related processes need to be assessed to develop a holistic idea of the behaviour and fate of nanoparticles in soil. Also, the repercussions of the use of nanoparticles on beneficial microorganisms need to be examined. The mechanism involved in the interaction of nanoparticles with the rhizospheric microbiome needs to be elucidated further. Integration of nanomaterials with biological control agents and organic additives would prove beneficial in mitigating soil-borne diseases along with crop produce intensification. However, the technology is still in its infancy and demands extensive research in this arena. Further, nanocomposites can be developed using active ingredients and fertilizers for holistic development of agricultural crops.

Nanopesticides would require more than a decade to reach the market and its end users. Most of the nano-formulations or products are still in the laboratories or start-up phase and fewer products have reached the market till date. In 2019, the global market of nano-based materials was estimated as 8.5 billion US dollars and it was anticipated to flourish at an annual rate of 13.1% from 2020 to the year 2027 (Anonymous, 2016). The increase in market share of nanomaterials in different field is attributed to increase in social acceptance and demand and adoption in different arenas such as medical, food industry, agriculture, sports, aerospace, energy sectors and many more. However, acceptance of nano materials in agriculture is quite low as it is closely related to food and human health. The high initial production cost and complexity in production process makes its use in agriculture debatable. It is well known that nanomaterials synthesized through physical and chemical methods are enormously expensive and pose environmental risk. The green synthesis methods are comparatively cost effective and profitable in long run, less hazardous to the ecological health and have faster reaction rate. Efforts are made globally for regulating secure manufacturing and applications of nanomaterials and nanodevices by supervision and advices or by legislations (Choi et al., 2009). Till date, there is no single law fully committed to offer guidelines related to use of nanotechnology in any country across the globe. There is a need for guidelines and directives to assess impending hazards and for suggestions to ensure safe utilization of nanotechnology and few organizations are working actively in this field such as International Standard Organization (ISO), Organization for Economic Cooperation and Development (OCED) or US Food and Drug Administration (FDA) (Coles and Frewer, 2013). The cautious assessment of benefits of use of nanoparticles throughout its lifecycle addressing environmental, social and economic implications as well as occupational safety and health hazards are need of the hour. The effect of nanoparticles on agricultural, industrial and non-industrial workplaces and measurement of exposure of workers in the workplaces is important. Also, the toxicological properties of nanoparticles should be characterized and gathered information must be stored in database which can be readily accessed by researchers. In nanoparticle manufacturing plants, safety measures should be prioritized to eliminate occupational hazards. Also, safety guidelines should be established in laboratories concerning safe handling, use and disposal of nanoparticles and related waste materials. Proper care should be taken while promoting the benefits of use of nanoparticles in agricultural field so that no adversities result from their use.

Further research is needed to determine the practicability, sustainability, efficiency, applicability and releasability of nanotechnology-based products under field conditions as well as to validate these technologies in comparison to present technologies. Also, more in vivo and field trials are to be conducted for pesticide loaded nanomaterials or nanopesticides. To get comprehensive idea on efficacy of these pesticides, long term trial data is required which is constraint at present. Unlike chemical pesticides, nanomaterilals and nanopesticides lacks a clear definition by regulatory authorities. Kookana et al. (2014) reviewed into great detail about how the effects of nanopesticides, in contrast to conventional pesticides, may rely on the uptake, bioavailability, concentration, and toxicity of the nanoparticles as well as the ratio of the active coupled to them. There is also little information available on the problem of pesticide resistance and potential ways that adding nanoparticles could lower its prevalence. The creation of regulatory standards for risk assessment is not possible without the use of extensive analytical techniques. The application of pesticides in field undergoes rotation and revision by regulatory bodies periodically restricts and ban the use of chemical pesticides thus, broad range of nanoformulations need to be available for future applications. Using new tools and methods to produce solid data for analysis, characterization, and risk assessment may be the key to receiving approval from regulatory authorities.

Thus, for logical selection of appropriate nanomaterials and nanopesticides, a thorough knowledge of the structural characteristics of the nanoparticles, including their shape, size, functional groups, and active adsorption/loading capacity is essential. In order to undertake biocompatibility and efficacy investigations at the cell, organism, and pest-host ecosystem levels under as-close-to-field circumstances as feasible, it is also crucial to choose a trustworthy and reproducible system. Further, wholesome development of nanoscience requires integration of different sciences such as biologists, agricultural engineers, plant pathologists, biotechnologists and soil microbiologists. Therefore, efforts must be directed toward creating a soil disease control strategy that is long-lasting, safe, effective, and environmentally benign.

PD was responsible for writing guidance and manuscript preparation. AK was responsible for writing the first draft of the article. PD revised the article with other coauthors. All authors contributed to the article and approved the submitted version.