Nanotechnology: Past, Present and Future Prospects in Crop Protection

Nanotechnology is an advanced and evolving discipline in the field of science and technology with various applications in other fields such as the life sciences, and is increasingly important in the plant sciences as well. It is estimated that 20–40% of crops are lost each year due to plant pests and pathogens. The current plant disease management, which primarily relies on toxic pesticides that may be harmful to humans and the environment, has the benefit of utilizing nanotechnology. It has capabilities in determining the outbreak of an epidemic as well as diagnosing different types of diseases. It can also distinguish between similar microbes like bacteria, fungi, viruses, complex genomic portions, and how two versions of genes on an individual chromosome differ. This chapter will cover the plant disease management implementation of this technology.


Introduction
Nanotechnology is a versatile discipline which embraces information from natural science, chemistry, physics and other fields. Sustainable crop production experiences approximately 20-30% of its total annual loss due to plant infection [1]. Food sustainability has been identified as one of the biggest problems of humanity faces. Conflict has plagued nations, societies, and administrations for a long time. Attack by plant pathogens on either cash crops or food crops results in decreased yields, economic loss, and possible crop damage [2,3]. There is a constant increase in the global population therefore the main challenge is how to meet the growing population's needs while reducing the stress on the environment. Controlling the spread of disease appears to be a main task at times. Nanotechnology is described as the operation or assemblies of discrete atoms, molecule, or molecular collections into structures in order to generate novel or extremely diverse assets [4]. The application of nanotechnology in agriculture can modify the agricultural science with advanced apparatuses for quick infection recognition, directed dealing, improved plant nutrient absorption, microbial infection resistance, and ecological stress resistance. Agronomic production will benefit from smart sensors and smart delivery systems to combat viruses and boost the harvest.
Moreover, the early and efficient pathogen detection is critical for infection resistance and disease management, thus helping to reduce yield damage. Magnetic nanoparticles, quantum dots, and gold nanoparticles are all commonly used nanoparticles for molecular detection. Gold nanoparticles, because of their unique characteristics such as small size, catalytic and surface effects, are frequently utilized for rapid insusceptible identification. Gold nanoparticles are capable of exhibiting covalent bonding with DNA, which allows it to be used for DNA assessment and reorganization. At the preliminary phase, nano-based applications are used for detection, diagnosis, and controlling of plant pathogens due to the application of safeguards for plant harvesting.

Defining nanotechnology in agriculture
The US Environmental Protection Agency has defined nanotechnology as the science of understanding and control of matter at dimensions of roughly 1-100 nm, where unique physical properties make novel applications possible [5]. This definition is somewhat inflexible when it comes to size dimensions. Materials could have received a greater emphasis on their problem-solving abilities. The particles referred to in this definition have "particulate between 10 and 1,000 nm in size dimensions that are simultaneously colloidal particulate" [6,7]. Ultimately, When the research into nanotechnology has been completely explored, it can be said to be the science of designing and building machines in which every atom and chemical bond is precisely specified. Rather, it is not a particular collection of techniques, devices, or products, but rather the full capabilities that we will be able to attain when our technology nears the theoretical limits set by atomic physics [8]. The "assembler" is Drexler's ultimate goal for nanomachine technology. The assembler is a nano-machined machine that is used to conduct routine operations at the atomic level [9]. The various types of nanoparticles are described below, along with their definitions and potential applications in plant pathology ( Table 1).

Nanoparticle for plant fungal disease management
Nanotechnology may play a key role in providing healthier food by promoting precision farming [11], in particular when facing huge losses due to a wide range of phytopathogens [12]. Agrochemicals use in farming are seeing a dramatic reduction due to the increasing popularity of metallic NPs. With the potential to eliminate targeted microbes from plants, soil, and hydroponics, they have outstanding capabilities [13,14]. NPs can be used to combat phytopathogens directly, as well as in developing fungicides [15]. Foliar sprays can be used to eliminate pathogens by NP application and also helps in plants growth [16]. Coefficient of variation is increased in low concentrations to control pathogens [13,17]. Metallic NPs cause hyphal plasmolysis, damaging fungal cell walls, resulting in cell death [18]. Some scientists believe that each agent has a different mechanism of action, whereas others claim the different mechanisms of action vary [19][20][21]. They include: 1. Permeability of plasma membrane, which is disturbed preventing a proper functioning due to attachment of the NPs proteins sulfur groups.
3. Disturbance of electron transport chain and protein oxidation. 4. Reactive oxygen species (ROS) may be generated, which cause cellular damage.
All of the mechanisms mentioned above have interconnected and exert interdependent effects on pathogens [22,23]. As part of a new technology that attempts to synthesize metallic nanoparticles, bio-reduction reactions have been evaluated for bio-reduction of different metals (e.g. iron, silver, zinc, gold, copper). In vitro and in vivo tests have also been done to see if metallic NPs have antimicrobial potential.

Nanotechnology based detection of plant diseases
Several plant species have been designated as hyper-accumulators, meaning that they have a high capacity to concentrate trace metals and then use those NPs [24]. Silver, silica, gold, zinc, and copper are frequently used metallic nanoparticles as antimicrobial agents. Silver nanoparticles were shown to be antimicrobial in both ionic and nano forms, and when tested and studied, the particles were shown to be capable of killing plant pathogens [25]. Silver has a strong antifungal and Technology in Agriculture antimicrobial mode of action against bacterial and fungal pathogens [26][27][28]. Fungicides' hydroxyl radicals-like degradation of fungal and bacterial cell material is achievable with copper NPs [29,30]. Since the size of these nanoscale copper particles helped control bacterial blight of rice and mung bean leaf spot disease, they were considered useful [31]. This is something you could try if you have plants that are ill or weak. Silica NPs would assist in the acquisition of resistance to diseases and in the activation of plant physiological mechanisms [32]. Iron NPs come into direct contact with fungal cell membranes and disturb the cell's permeability, reducing the cell's growth and eventually causing death through the development of oxidative stress [33]. In solution, zinc NPs release hydroxyl and superoxide radicals, destroying fungal cell walls, hyphae, and preventing conidiogenesis, all of which leads to cellular death [34,35]. The gold NPs had greater toxic effects on Salmonella than on its macroform [4]. As of now, there is no evidence to suggest that silica itself has any antimicrobial capability, but it can indirectly promote plant disease resistance and other stress resistance [36,37]. For some plant diseases, nano-silver was found to be highly effective [13]. Nano-sized mesoporous silica particles feature a regular pattern of pores with increased surface area. It's improved delivery, efficiency, and effectiveness for site-specific chemicals.

Fungicides (Nano fungicides)
Nano-scale materials development has seen considerable progress in the recent years, with distinct characteristics from corresponding bulk materials. Nanotechnology promises a bright future while delivering pesticides in a safer manner [38]. Agrochemicals have enhanced solubility when polymeric Nano fungicide formulations deliver them at a slow rate, thus increasing their bioavailability [39,40]. Nanofungicide developed and tested so far proved effective in plant protection strategies [41,42]. For developing Nano fungicides, we should opt for Nano emulsions (NEs) with smaller size, lower viscosity, and higher stability [43]. The active fungicide ingredient is placed within a core surrounded by a membrane in a nanocapsule. Additionally, nanoencapsulation could be utilized in nanopesticide formulations. Polymers and inorganic compounds have been tested for their possible use in nanopesticide formulations for crop protection [44]. For these formulations to be as potent and stable as possible, while still meeting the safety criteria of the systems to the environment and human beings, it is critical that more work be done. Nanotechnology has a large capacity to develop completely new systems and formulations [45].

Herbicides
They aimed to improve low water solubility, decrease volatility and to deliver the active molecules slowly. Organic solvents are needed to help solubilize insecticides that have low water-solubility, which increases the cost and toxicity. To decrease toxicity, nanoparticles may be used to increase solubility. Another problem that occurs following insecticide application is the evaporation or volatilization of the active ingredient. Even though essential oils have a reputation for causing insecticidal effects, the unstable chemical nature of the substances in the presence of air, light, moisture, and heat causes them to rapidly evaporate. Another motivation for the development of Nano-insecticides is to make the active molecules more stable, which would help ensure that they release at consistent rates over time, resulting in a reduction in insecticide usage while also improving the safety of humans and animals. Whereas fipronil, a commercial insecticide, extended the 100 percent mortality window by 3 days, compared to that commercial product, fipronil-loaded silica extended the 100% mortality window by 3 days, allowing better control of the colony. In groundnut bruchid storage conditions, utilized azadirachtin-loaded zinc oxide or chitosan nanoparticles, and examined the effectiveness over 180 days. The groundnut bruchid, 54.61% of the total weight, was found in the Neem seed kernel extract, loaded into zinc oxide nanoparticles, when compared to the other formulations tested [46]. If the gradual release of active molecules decreases toxicity, then this could also potentially lower the toxicity of insecticides. The results of these studies are promising, but additional studies are required to fully confirm the reductions in insecticide toxicity.

Insecticides
The use of nanosized preparations or nano-materials based herbicide formulations offers unique opportunities for delivering chemical or biological pesticides. Herbicide formulations based on nanomaterials may be more effective, have better solubility, and reduce toxicity than conventional herbicides. If early-stage weed control is employed with the use of nanoparticle-based herbicide release systems, the resistance potential will be minimized while the active ingredient's effectiveness will be maintained and prolonged release will be prolonged [47]. Herbicides can be selective, killing only target weeds, or non-selective and potentially hazardous to people and the environment if they kill all vegetation. Before seedlings sprout up from the soil, you can apply a pre-plant, pre-emergence, or post-emergence herbicide (weed seedlings already emerged from the soil).

Nano-phytopathology
New techniques such as nanotechnology will remain novel for this century, but as time passes and extensive research is done in the field, they will be more widely used in the treatment of plant infection. Plant pathology is set to offer an exciting future of research with regard to their antibacterial and antifungal properties in the context of nanotechnology. Using nanoparticles to protect the seeds and foliage from pathogens that would otherwise intrude can be the most effective method. Therefore, it can be summarized here that nanoparticles can play their role in plant disease management in following ways-.
• Nanoparticles being used as pesticides themselves and being applied to plants directly for the control of disease.
• Nanoparticles as carriers of other pesticides/nanoparticles for their controlled and targeted release and to increase their effect.
• Nanodevices to detect diseases at early stages.
Nanoparticles can be successfully applied to disease affected plants with enhanced and effective results due to their extremely reactivity/affectability. This increased reactivity can be attributed to their extremely small size and large surface area.

Effect of nanoparticles on the pathogens/microorganisms
After scientific testing, scientists have confirmed that the chemical and physical properties of nanoforms of materials actually shift between their macroform and nanoform. All of these properties transformations ultimately end up with useful real-world applications in plant defense and plant protection. Since nanoparticles have the advantages of both small size and surface area, they influence plant pathogens in a more precise way. Larger macroscopic entities are less likely to interact with microorganisms because they are farther away from them. There is an abundant amount of evidence available to bolster this claim.

Effect of nanoparticles on Bacteria
New research shows that nanoparticles have antibacterial properties, which is most likely the result of the cell wall of the bacteria being broken or of high levels of reactive oxygen species (ROS) being produced [48][49][50]. Bacterial infection is a leading cause of contamination and mortality due to prolonged presence of pathogens. Due to low cost and positive results, antibiotics have been selected for the treatment of bacterial contamination. Although multiple studies have demonstrated that overuse of antibiotics leads to multidrug-resistant bacteria strains, this has not yet been confirmed though. A very powerful strain of antibiotic-resistant bacteria has emerged. Previous researches states that, these kinds of bacteria consist of gene, which are super resistant [51]. The mode of action of nanoparticles is directly linked with the bacterial cell wall, which enables the nanoparticles to control super-resistant bacteria. Bacteria may become resistant to nanoparticles if they are exposed to them. If these new NP-based materials are able to perform antibacterial activity, it's entirely possible [52][53][54].

Nanotechnology for plant viral diseases
The various types of nanoparticles were investigated and used to control Sitophilus oryzae and baculovirus BmNPV (Bombyx mori nuclear polyhedrosis virus) in silkworm (B. mori) disease caused by S. oryzae and BmNPV [55]. To complete their investigation, the researchers performed bioassay, which involved preparing the nanoparticles' solid and liquid formulations; after which, they applied these formulations to rice and stored it in a plastic box with 20 adult S. oryzae for seven days. On the first day, the researchers reported that hydrophilic silver nanoparticles were most effective. More than 90% of mortality was gained on day 2, and silver and aluminum nanoparticles were the primary source. Seventythree percent of the insects died after seven days of exposure to lipophilic silver nanoparticles. But with respect to nanoparticles of aluminum, 100% mortality was observed. Thus, a significant decrease in viral load was found in a hydrophobic aluminosilicate nanoparticle suspension when B. mori leaves were used in an ethanolic treatment of grasserie disease.

Metallic nanoparticles: effective tool for plant disease management
There are different nanotechnology approaches for the detection of plant diseases (Figure 1).

Bio-nano materials
There are some bio-nano materials which are categorized through X-ray diffraction (XRD) technique, X-ray photoelectron spectroscopy (XPS), Energy-dispersive X-ray spectroscopy (EDS), UV visible spectroscopy, scanning electron microscopy (SEM), Fourier transforms infrared spectroscopy (FTlR), Coupled plasma spectrometry (ICP), Transmissions electron microscope (TEM) and Atomic force DOI: http://dx.doi.org/10.5772/intechopen.98703 microscopy (AFM) techniques. These bio-nano materials played noteworthy role in field of agriculture, medicine and biology. The increasing usage of bio-nano materials in many areas will enhance their productivity in the atmosphere by developing more analytical tools in nanotechnology for controlled environmental risk management [56]. Bio-synthesis of bio-nanomaterials can be also achieved by using plant extracts [57], microbial cultures or their enzymes and proteins.

Nano bio-barcode assay
The technology of biological barcodes is improving in nanotechnology and incorporating new advancements in nanotechnology to aid in the identification of nonenzyme-containing ultra-sensitive proteins and DNAs. Instead of using an orthodox ELISA, a protein barcode assay could be employed, which is both more complicated and far more sensitive and profound. Because of its dependence on nanoparticles, the nanoparticle-based biobarcode assay is more sensitive to finding pathogens than traditional techniques like ELISA, Real-time PCR, etc. [58,59]. It can also help in early detection of plant diseases. The biobarcode technique consists of two probes.

Magnetic micro beads (MMB): Target recognition and carry an antibody or
DNA as a biological probe.

Gold nanoparticles (Au-NP):
It has a polyclonal antibody or an oligonucleotide (Bio-barcode) Bio-barcode is a developing technique with the help of advancements in nanotechnology. It is an enzyme free, PCR free technique and highly sensitive for protein and DNA detection.
Moreover, the advancement has been made on different aspects of Bio-barcodes to make it more applicable in fields. DNA barcoding has been suggested for fungal identification [60]. It has been reported to be reliable and rapid method of detection. A DNA barcode should be standardized and scalable. And also, the similar techniques can be developed for speedy and onsite detection of plant pathogens particularly viruses to decrease the losses to crops.

Nanopore system
Nano pore used in nano-pore systems can be used to examine genetic information at a low cost, have low sample preparation requirements, and operate quickly [61]. In fact, nanopore is a nano-sized pore through which a flow of nanoparticle ions is flowing. When there is a change in the current, it shows that an analysis of the biological molecule is in progress. Nanopore-based systems determine nucleotides through conductivity changes, which enables them to identify nucleotides because of their lipid membrane [62]. A protein nanopore is injected into a polymer bilayer membrane, which contains a sensory chip to measure current that is associated with the identity of the molecule [63].
Newly, nanopore based sequencing (Nano-SBS) distinguished four DNA bases through discovering four different sized tags released from 5′-phosphate-modified nucleotides at the particular molecule level for sequence determination [64].
Recently, UK-based nanopore technology, a portable DNA sequencing machine (MinION) has been released. It enables researchers to sequence a 10 kb sample of single-stranded DNA as well as double-stranded DNA, making next-generation sequencing easily approachable [65].
The discovery of this new technique offers both the ability to detect and track the spread of an epidemic, as well as the ability to differentiate between various bacteria, fungi, viruses, complex genomic components, and difference between two different gene sequences located on the same chromosome. In other words, a nanopore platform that is already inside a current diagnostic machine can conduct whole genome analysis in minutes. It could be used for analyzing plant and pathogen genomics for the purpose of increasing agricultural crops.

Nanodiagnostic kit
Nanodiagnostic kit also called "lab in a box" is used as a small box for measuring important tasks in plants which can be done in small space [66]. A smart kit helps to detect the plant pathogens and can help the farmers in prevention of wide spread diseases [1,67]. Nanodiagnostic kit contained four myco-sensors which can detect the of ZEA, T-2/HT-2, DON and FB1/FB2 myco-toxins on only one strip used for cash crops like wheat, barley and corn [68]. This method is fast, convenient, and less expensive for finding out if crops have a fungal infection. Antigen and antibodies, the nucleotide sequence in which nano kit can be used, all have multiple additional purposes. Moreover, it can also detect particular gene target, isolation and purification of specific genes. But nano kit has not fully checked practically for the plant pathogen detection in field conditions. More extensive research works are still needed in this field.

Quantum dot (QDs)
This is another level of nanocrystals that release specific wavelengths of light: Quantum Dots (QDs). There are three-dimensional nanoparticles that have a broad excitation spectrum [69]. Narrow-tunable emission peak, extensive fluorescence lifetime, resistance to photo bleaching, and molar extinction coefficient ten to one hundred times higher than for most QDs. However, one of the findings revealed multiple enzymatic properties of QD-based nanosensors [70] and stated CdTe quantum dots usage as biosensors with specific antibiotic coatings against Polymyxa betae specific glutathione-S-transferase (GST) protein [71]. Because of the interaction of CdTe quantum dots and rhodamine, which cause a resonance dipole-dipole coupling, the resonance dipole-dipole coupler, which is required for fluorescence resonance energy transfer, is created (FRET). For more efficient results, this device can be used to test plants in under 30 minutes. Although it was concluded that there was a highly sensitive detection of diseased lime trees by showing 100% specificity with a sensitive detection limit for P. aurantifolia, the opposite appears to be true in this instance, according to the findings of this study what [72]. DOI: http://dx.doi.org /10.5772/intechopen.98703 In the near future, quantum dots will be used in almost every form of diagnostics and medical testing. For example, fluorescent QDs can be used for a variety of molecular diagnostics and genotyping procedures. Additionally, these studies contribute to the complex diagnosis and combination with therapies which help lead to possible cancer diagnosis applications. QD bio conjugates enable the visualization of living cancer cells in animals and the visual differentiation of cancer cells in the context of a fluorescence microscope.

Future prospects of nanotechnology in plant disease management
To find out more about using NMs in plant sciences, we have covered all relevant aspects here. According to recent researches, the use of nanotechnology has resulted in considerable advancements in the development of NMs and their implementation in medicine for the detection and treatment of illnesses. This is where NMs (naturally occurring mini-molecules) for plants has fallen short. Concluding remarks: Additional studies are likely needed to optimize this synthesis and biofunctionalization direction for plant applications, but also to investigate further the underlying mechanisms of plant uptake, especially with regards to sustainable agriculture. The significant aspects of plant physiology that have thus far gone undocumented are something that the applications will need to support. Nanobiosensors for monitoring plant development and interactions with the environment, especially in controlling growth conditions, could be a means of improvement. Polymeric and hydrogelbased NPs, because of their safety profile, high loading capacity, and resistance to degradation, offer undeniable advantages for drug delivery. This unique NMs strategy is elegant in that it allows for the spatial and temporal cargo release from cell and animal models based on environmental cues (e.g., UV, NIR, ultrasound, etc.) [73][74][75]. Finally, as a final remark, we encourage multidisciplinary approaches for designing and synthesizing smart nanomaterials, in order to help expedite plant nanotechnology. The point of such a project is to open new horizons in phytonanotechnology by uniting complementary professional competencies, including those of plant biologists, geneticists, chemists, biochemists, and engineers.
Every sanitation/quarantine strategy requires that infested or infected material be discovered ahead of time, because any greenhouse, field, state, or country where this treatment is used is inevitably where you find infested or infected material. In order for this operation to succeed, prompt detection of pathogens is critical. There are large advances in the speed and sensitivity of pathogen probes with the introduction of nanotechnology. Nanoparticles can be used as rapid diagnostics for the detection of bacterial, fungal, nematode, and viral pathogens, which can help in the early detection of diseases [76,77]. Pathogen detection has only recently been explored with super paramagnetic iron oxide nanoparticles, though the techniques have been pursued in other applications for nearly a decade [78,79]. Nanoanalytical devices employ a biologically-integrated sensing element with a transducer built into it to form an electronic signal when they come into contact with the analyte of interest (pathogen). However, Nanotechnology innovations in the last decade have greatly reduced the technical barriers of making biosensors with a variety of nanoparticles and nanostructures [80].
Moreover, this novel use of nano-enabled biosensors to monitor, map, and treat specific areas in a field prior to or during the onset of symptoms can be coupled with robotics and GPS systems to produce smart delivery systems that monitor, map, and treat locations prior to or during symptoms appearing. This new technology could help farmers reduce their use of agrochemicals while also increasing yield and profits [81,82]. Biosensors, being capable of detecting pathogens with a higher level of sensitivity, can also be used in ports of entry, where quarantined pathogens can be apprehended with greater efficiency. When food pathogens and mycotoxins are detected quickly, the value of rapid analysis is obvious [83][84][85]. Applications of nanotechnology in plant disease management and crop improvement are shown in Figure 2.

Limitations and future directions of nanotechnology
Nanotechnology with promising results in the agricultural sector, such as its unique method of applying pesticides, fertilizers, and so on, may finally allow the human population to visualize the dream of achieving sustainable and ecofriendly agricultural technology. Recent findings have shown that nanomaterials could potentially harm a beneficial soil organism, the earthworm [86]. Xu et al. [87] summarized increased safety concerns regarding nanomaterials in food and agriculture. They concentrated on the most common exposure routes and factors involved in nanotoxicity. More and more engineered nanomaterials are reaching the environment, due to new technologies. Production scale and cost currently limit the application of nanocarriers in agriculture. Large-scale manufacturing of nanomaterials and its effective application to agriculture will greatly reduce the cost. The difficult commercialization of nanomaterials for agricultural applications necessitates wellprotected materials, superior testing priorities, a clear-cut risk assessment, and international regulatory guidance [88]. However, a concern has been raised on the impact of increased nanomaterial production on ecosystem health. Many commercial nanomaterials are more toxic than their bulk-form counterparts, even though bulk-form nanomaterials are legally allowed for sale. There still needs to be further research on the various applications of nanomaterials, such as synthesis, toxicity, and its use at the field level. Even the dream of utilizing nanotechnological methods in agriculture is still in its infancy. As a result, the focus areas that require further investigation are the development of systems that would improve the release profile of herbicides without altering their characteristics and novel carriers with enriched activity without significant environmental damage. There are some examples of recent breakthroughs in nanotechnology in agriculture ( Table 2) [89].

Conclusion
Nanotechnology has the potential to improve plant growth, disease resistance and nutrient use with controlled delivery of agrochemicals. More efficient and targeted use of fungicides, herbicides and insecticides may be seen through using environmentally friendly nanocapsules. In order to preserve the freshness and quality and help in disease prevention, post-harvest nanotechnology research and development is needed. As the use of nanotechnology progresses, applications of green chemistry have reduced the use of toxic solvents, allowing for crop protection. Through use of biotechnology and nanotechnology, crop protection and production are now available to a much larger portion of the population. Despite being unverified, the effects of nanomaterials on the environment are clearly noticeable because of their unique physical and chemical properties. Nanomaterials application in agriculture is new, and further research is required. Nanomaterials are expected to have a huge impact on the pricing and environmental friendliness of crop protection techniques. With the application of nanotechnology, new methods will be developed for managing disease in greenhouses and fields, while advancements in disease diagnostics and the construction of molecular manipulations of plants and pathogens will be made possible. However, only a few laboratories are currently exploring the incorporation of nanotechnology into phytopathology, but we expect that as new research is geared toward discovering, adapting and applying nanotechnology, the barriers to global food production will be lessened.