Biological Seed Coating Innovations for Sustainable Healthy Crop Growth in Tomato

Abstract

Biological seed coating (BSC) is the fastest-growing segment under the seed treatment approaches in the global seed market. It refers to the application of certain beneficial microbes to the seed prior to sowing in order to suppress, control, or repel pathogens, insects, and other pests that attack seeds, seedlings, or plants. Beneficial bioagents along with the compatible adjuvants can safely be delivered through coatings onto the seed surface. The polymer acts as a protective cover for bioagents and helps in improving the shelf life and dust-free seed. It is an efficient mechanism for placement of microbial inoculum into soil where they colonize the seedling roots and protect against soil-borne pathogens. It is also used to increase the speed and uniformity of germination, along with protection against soil-borne pathogens in nursery and improves final stand. Some induces systemic resistance in plants against biotic agents. It is a low-cost, alternative viable technology to chemical-based plant protection and nutrition. Thus, the demand for biological seed treatment solutions is increasing in view of consumer acceptance for chemical-free food. They give protection to seedlings in the nursery against damping-off fungi like Fusarium spp. or Rhizoctonia spp. and improve crop growth and yield in the main field.

1. Introduction

Tomato (Solanum lycopersicum L.) is the second-largest global vegetable crop next to potato [1]. Tomato is known for its rich source of vitamins (A and C), minerals (potassium and folate), and antioxidants (lycopene and beta-carotene) with low calories and fat, making a healthy and balanced diet. Tomatoes are widely consumed as raw, cooked, canned, or processed products and contribute several health benefits like reduced risk of heart disease, certain cancers, and age-related macular degeneration and also improves overall digestive health. However, the production is threatened by various biotic and abiotic stresses. Among biotic stresses, tomato is affected by several fungal, bacterial, and viral diseases like damping-off (Pythium aphanidermatum), early blight (Alternaria solani), late blight (Phytophthora infestans), etc. Damping-off caused by Pythium spp. is an important nursery disease [2], which results in massive seedling death affecting qualitative and quantitative yield losses [3]. Moreover, seed and soil-borne fungi like Phytophthora, Pythium, Rhizoctonia, and Fusarium spp. can cause damping-off diseases that not only kill seeds and lower stem of seedlings but also create problems in emergence [4]. Biological stress is a complicated phenomenon that occurs in the field and is brought on by many pathogen types [5, 6, 7, 8]. Due to non-availability of resistant cultivars in tomato, the disease is managed by the use of synthetic pesticides [3]. seed and soil-borne diseases are more difficult to control with chemical seed protectants [8, 9, 10, 11, 12]; chemicals used in seed treatment pose a potential hazard to human health [13, 14, 15], bees [16], birds [17, 18], and soil microbes [19, 20], which could ultimately slow down plant growth [21].

Moreover, the global biological seed treatment market size was valued at USD 1.28 billion in 2022 due to the adoption of biological seed coating by key players of seed industry in view of surging demand for chemical-free foods. It is expected to grow further at a compound annual growth rate (CAGR) of 12.4% from the year 2023 to 2030. Among these, the microbial segment contributed over 65% in 2022 and is expected to grow at a CAGR of 11.8% from 2023 to 2030. The seed protection segment is the largest market share holder among them, occupying 67%, in terms of revenue during 2022. The rising inclination of consumers toward maintaining a healthy lifestyle and the rising demand for chemical-free food products have fueled the increased use of biopesticides for treating vegetable seeds, accounting for the highest revenue share of over 25% in 2022 with a CAGR of 12.7% from 2023 to 2030 [22].

In view of harmful effects encountered with the usage of synthetic pesticides, there is a need to shift for alternative protection measures in vegetable production [23, 24, 25]. Several studies have proved the effectiveness of biological control agents in controlling various seed and soil-borne diseases caused by Pythium spp. and Rhizoctonia solani [26]. It has been reported that Trichoderma spp. was found effective against Fusarium oxysporum and R. solani [27], whereas the metabolites produced by Bacillus subtilis showed antibiotic activity in suppressing damping-off caused by R. solani in tomatoes. Onion seeds coated with Pseudomonas fluorescens F113 reduced damping-off disease [28]. In addition, the microbial agents also enhance plant growth parameters [29] by improving the uptake of micro- and macronutrients [30, 31]. For instance, Bacillus spp. and Trichoderma spp. are known for their growth promoting properties [32, 33]. In greenhouse conditions, antagonistic bacteria and fungi showed successful control of tomato diseases like blight, damping-off, bacterial and fungal wilt, powdery mildew, anthracnose, and leaf spot [34, 35, 36]. Hence, seed treatment with bioagents protects the germinating seedlings against seed and soil-borne pathogens apart from adverse abiotic conditions and thus helps in maintaining the initial plant population, which in turn will result in a 10–12% improvement in crop yield. Through the metadata analysis across crops, target pathogens, regional climates, and conditions of experiments, Lamichhane et al. [37] reported that compared to untreated seeds, the effects of biological seed treatments on seed germination, seedling emergence, plant biomass, disease control, and crop production were all considerably higher (7 ± 6%, 91 ± 5%, 53 ± 5%, 55 ± 1%, and 21 ± 2%, respectively). Moreover, biological seed coating influences germination and seedling growth by acting as biostimulants [38]. Keeping this in view, biological seed coating is an emerging technique of seed treatment in which antagonistic microbes are blended with compatible adjuvant and applied to seed surface. The bio-friendly polymer is proven to be a superior substitute for the common sugar syrup adjuvant [39, 40]. This technique takes an environmentally friendly approach by selectively using fungal antagonists to combat soil and seed-borne diseases, perhaps providing an alternative to chemical management [28]. Although the idea of treating seeds with biological agents is not new, historically, seeds are often treated prior to sowing. There are very few studies in India that advocate seed treatment with biological agents on a large scale right after cleaning and processing the seed.

2. Need of biological seed coating

The necessity for biological seed coatings is typically driven by the demand to improve crop health, reduce environmental impact, and adhere to changing regulatory standards. Biological seed coatings promote reliable and sustainable agricultural activities by utilizing the advantages of beneficial microbes and tailored/customized/adapted treatments.

The statistics on the use of biological seed coatings are meagerly available because of the diversified products and varied interests of the industry. However, due to a shift toward organic farming, and the requirement for efficient and eco-friendly seed treatments, in the recent past, a steady growth in their usage has been observed across agricultural and horticultural crops with a customized option based on crop-specific requirements. As it promotes biodiversity, BSC is a sustainable and alternative approach to conventional chemical seed treatments. The growing health concern among consumers against agrochemicals creates a wide scope for the adoption of sustainable agricultural practices and eco-friendly seed treatments for the commercialization of biological seed coatings in the near future.

Efforts are needed to improve the efficacy, stability, and compatibility of biological seed coatings, through enhancing formulations, developing improved delivery systems, and exploring new combination strains of beneficial microorganisms.

The regulations and certifications on the usage of biological seed coatings can be subjected to a particular country or region based on product efficacy, safety, and labeling. In case of organic certifications, compliance is required for specific standards with regard to biological seed treatments.

3. Benefits of biological seed coating

Through the biological seed coating technique, beneficial microbes maintain a symbiotic relationship with the seedlings and contribute to many benefits such as enhanced seed germination and seedling vigor, increased resistance toward pests and diseases, and efficient nutrient uptake and productivity.

Enhanced seed germination and seedling establishment: The microorganisms used in the seed coating can stimulate germination, improve seedling vigor, and enhance early root and shoot growth, resulting in quicker and more uniform emergence of seedlings.

Disease suppression: Certain microorganisms in the seed coating can have antagonistic effects against pathogens and suppress seed and soil-borne diseases. They may produce antibiotics or compete with harmful organisms for resources, thereby protect the seedlings from infections.

Nutrient availability and uptake: Some microorganisms, especially the mycorrhiza, has the ability to solubilize nutrients, such as phosphorus, and make them available to the developing plants. This can enhance nutrient uptake efficiency and support plant growth.

Environmental stress tolerance: Bioseed coatings contain microorganisms that produce compounds that help the plants to tolerate various environmental stresses, such as drought, salinity, or temperature extremes. These microorganisms can promote stress tolerance and improve plant survival under adverse conditions.

Reduced chemical inputs: Use of biological seed coatings, which is cost effective, can reduce the reliance on chemical treatments, such as fungicides or insecticides, as the beneficial microorganisms can provide natural protection against pathogens and pests without affecting the soil fauna.

Compatibility with other seed treatments: Bioseed coatings can be used in conjunction with other seed treatments, such as insecticides or fungicides, without significant interference. This allows for integrated pest management strategies and customized seed treatments in addition to reducing the cost of inputs.

Enhanced soil fertility: Applied BCAs continuously multiply in the soil and help in the improvement of its fertility.

4. Organisms commonly used for biological seed coating

Selection of the organism for biological seed coating depends on the crop being cultivated, benefit required, compatibility ensured, and effectiveness for specific application. The specific strains and species within the groups of organisms and their effectiveness may vary based on soil conditions, crop, and the region under consideration. It is crucial to note that the individual strains and species within these groupings of organisms might vary, and their efficacy can rely on factors including the type of crop grown, the soil, and geographical considerations. To ensure compatibility and efficacy for particular applications, the selection of the suitable organisms should be based on scientific study and field tests. Commonly used organisms for biological seed coating are included in Table 1.

Biological organism	Importance and mode of action
Trichoderma spp	Potential Biological Control Agent [41, 42, 43]. It is fast-growing, secondary opportunistic invader, having efficient rate of sporulation, which survives under adverse conditions; utilizes nutrients efficiently; produces antibiotics, cell wall-degrading enzymes like protease, beta 1–3-glucanase, and toxic metabolites [44, 45, 46]; and can induce systemic resistance in plants. Trichoderma species are beneficial fungi that can protect seeds and seedlings against soil-borne pathogens. After completion of the parasitic activity, host fungi cytoplasmic contents appear totally evacuated, and the hyphae look “translucent,” and the hyphal “exoskeleton” remains [47]. Five isolates of T. harzianum were also found antagonistic to the growth of R. solani in dual culture on PDA with sparse to intense coiling method of myco-parasitism followed by disintegration, disorganization, and death of R. solani mycelium [48]. Trichoderma spp. can improve the plant growth and yield by enhancing the growth hormones and increment of plant beneficial microbiome [49, 50, 51].
Bacillus spp.	The endospores produced by these bacteria are resistant to adverse conditions. Due to their antagonistic properties, Bacillus spp inhibit plant pathogen growth through the production of antibiotics and enzymes. Examples of this group include Bacillus subtilis, Bacillus megaterium, and Bacillus amyloliquefaciens.
Pseudomonas spp	Pseudomonas species, such as Pseudomonas fluorescens, have biocontrol properties and can suppress plant diseases caused by pathogens. Through the production of antimicrobial compounds, they can suppress plant diseases by outcompeting the pathogenic organisms for resources like siderophores, iron complexes, and so forth. They can induce systemic resistance [52] and also improve seed quality and reduce bacterial canker drastically [53].
Plant Growth-Promoting Rhizobacteria (PGPR)	PGPR are beneficial bacteria that colonize the rhizosphere (root zone) and promote plant growth. Examples include species of Bacillus, Pseudomonas, and Azospirillum. They can improve nutrient availability, produce growth-promoting substances, and help against plant pathogens. They are used to control the bacterial spot of tomato caused by Xanthomonas vesicatoria [34, 54, 55, 56].
Nitrogen-Fixing Bacteria	Certain bacteria, such as species of Rhizobium and Bradyrhizobium, are used in legume crops to establish symbiotic associations in root nodules by fixing atmospheric nitrogen and making it available to the plants.
Mycorrhizal Fungi	Mycorrhizal fungi form symbiotic associations with plant roots, improving nutrient uptake, particularly phosphorus. Examples include species of Glomus, Rhizophagus, and so on. They explore volume of soil by extending the root system with their hyphae.
Yeasts	Some yeast species, like Saccharomyces cerevisiae, have biocontrol properties and can help protect seeds, seedlings, and also postharvest pathogens by releasing antifungal substances and thereby initiating the defense factors in host plant [57].
Actinomycetes	Actinomycetes are potential biocontrol agents against of soil-borne plant pathogens like Fusarium spp. [58], Phytophthora spp. [59], Pythium spp. [60], Rhizoctonia spp. [61], and Verticillium spp. [62].

Table 1.

Organisms used for biological seed coating (table is extrapolated from other works).

5. Mechanism of biological control

Fungal and bacterial biological control agents use different mechanisms to control pests, pathogens, and invasive species. Specific fungal and bacterial biocontrol agents may employ multiple mechanisms simultaneously or have unique strategies depending on their characteristics and the target organisms. The selection of the appropriate biocontrol agent and mechanism depends on factors such as the target pest or pathogen, the specific crop or ecosystem, and the desired outcomes of biological control. Here are the mechanisms commonly associated with fungal and bacterial biological control:

Mutualism: It is an association between two or more species by which both species derive benefit. It contributes to biological control by fortifying the plant with nutrition and or by stimulating the host defenses. Obligatory interaction is observed between plants and mycorrhizal fungi. Facultative or opportunistic mutualism is observed between leguminous plant and Rhizobium bacteria.

Plant Growth Promotion: Some bacterial biocontrol agents not only suppress pests or pathogens but also promote plant growth [51]. These beneficial bacteria can produce plant growth-promoting substances like phytohormones, enzymes, or siderophores. They enhance nutrient uptake, improve stress tolerance, or stimulate root development, resulting in healthier plants with capacity better able to resist pest or pathogen attacks [55].

Protocooperation: It is a form of mutualism in which the involved organisms do not exclusively depend on each other for survival. Many of BCAs are facultative mutualists whose survival rarely depends on any specific host, and disease suppression depends on the prevailing environment.

Commensalism: It is a form of symbiotic interaction between organisms where one organism benefits, and the other is neither harmed nor benefited. Most plant-associated microbes are commensals with regard to host plant to which they contribute nothing, while their presence decreases the pathogen infection and disease severity.

Neutralism: Presence of one species has no effect on the other species.

Antagonism: It results in negative outcome for one or both.

Competition: The competition between and within the species results in decreased growth, activity, and fecundity. Biological control takes place when the antagonistic organism competes the pathogenic organism for nutrients in and around the host plant [55]. This will benefit beneficial organism at the expense of other. Bacterial and fungal biocontrol agents can compete with pests or pathogens for resources such as nutrients or space. They colonize ecological niches and outcompete the target organisms for nutrients and space, reducing their population size and limiting their ability to cause damage.

Parasitism: It is a type of negative symbiosis in which two unrelated organisms coexist for a long period. In this association, physically smaller parasite gets benefited by causing harm to the large organism called the host. Similarly, parasitism of virulent pathogen by beneficial organism leads to biocontrol through the stimulation of host defense systems. Some fungal biocontrol agents are mycoparasites, meaning they attack and parasitize other fungi. These biocontrol fungi invade the target pathogenic fungi, penetrate their hyphae, and extract nutrients eventually killing them. Mycoparasitic fungi can produce specialized structures like haustoria or adhesive structures to facilitate attachment and nutrient uptake [47, 48].

Hyperparasitism: Pathogen is directly attacked by the specific BCA and stops its propagation and kills it.

Hypovirulence: Reduction in disease-producing capacity of the pathogen. Coniothyrium minitans parasitizes sclerotia producing plant pathogens.

Predation: Killing of one organism by another for consumption and sustenance is referred as predation. For example, fungal feeding nematodes and microarthropods consume pathogen biomass.

Induction of host resistance: Some fungal biocontrol agents can induce systemic resistance (ISR) in plants [52]. When these fungi colonize plant roots or other plant tissues, they trigger the plant’s defense mechanisms, leading to the production of defensive compounds or activation of systemic signaling pathways. This enhanced resistance helps plants withstand attacks from pests or pathogens. Certain bacterial biocontrol agents can trigger systemic resistance in plants similar to fungal biocontrol agents. They colonize plant surfaces or enter plant tissues, activating the plant’s defense responses. This leads to the production of defense compounds, reinforcement of cell walls, or activation of signaling pathways, making the plant more resistant to pests or pathogens.

Antibiotic-mediated suppression: Many fungal biocontrol agents produce secondary metabolites, such as antibiotics, which inhibit the growth and development of target pests or pathogens [46]. These biocontrol fungi release toxic compounds into the environment that are harmful to the target organisms, suppressing their population growth or causing their death. Several bacterial biocontrol agents generate antimicrobial substances, which include antibiotics, toxins, or enzymes, which hinder the development and growth of pests or pathogens by intervening with important cellular functions, destroying cell walls, or obstructing nutrient uptake, eventually resulting in either death or inhibition of the target organisms. Bacillus subtilis also shown the ability to produce antibiotics and other metabolites against Pythium spp. [63, 64].

Suppression through lytic and other enzymes: Many BCAs generate and liberate lytic enzymes that hydrolyze polymeric compounds like chitin, proteins, cellulose, hemicellulose, and DNA and suppress plant pathogen activities directly.

6. Commercial bioformulations

These are the products available in the market that contain beneficial microorganisms or natural compounds used for various agricultural applications. Specific commercial bioformulations can vary depending on the region, crop, and regulatory approvals. These formulations are designed to enhance plant growth, improve nutrient uptake, suppress diseases and pests, and promote sustainable agriculture. The availability and formulations of these products may be subject to local regulations and market demands. Farmers and growers should consult with local agricultural suppliers or experts to identify suitable commercial bioformulations for their specific needs. Here are some examples of commercial bioformulations based on the utility:

Biopesticides: These are the formulations containing beneficial microorganisms or natural compounds used for pest management. These products may contain antagonistic bacteria, fungi, or viruses that can inhibit the growth or activity of plant pathogens. Examples include fungal biopesticides like Trichoderma spp., Beauveria bassiana, and Metarhizium spp. for controlling fungal diseases and targeting specific pests, Pseudomonas fluorescens for fungal and bacterial disease management, and Bacillus thuringiensis (Bt) formulations for insect control.

Biofertilizers: These formulations contain beneficial microorganisms, such as nitrogen-fixing bacteria (e.g., Rhizobium spp.), phosphate-solubilizing bacteria, or mycorrhizal fungi. These enhance nutrient availability and improve nutrient uptake by plants, promoting healthy crop growth and reducing the need for synthetic fertilizers.

Plant Growth Promoters: These bioformulations contain natural compounds or beneficial microorganisms that stimulate plant growth and development by enhancing root development, increase nutrient absorption, and improve stress tolerance.

Biostimulants: These are similar to PGPRs but with an added advantage of stimulating plant physiological processes and enhancing plant growth, vigor, and overall health of the plant. These products can include substances like seaweed extracts, humic acids, or plant growth-promoting rhizobacteria (PGPR).

7. Classification of commercial bioformulations

Commercial bioformulations are classified into two types based on the carrier material used 1) Solid formulation and 2) Liquid formulation.

7.1 Solid bioformualtions

Solid bioformulations refer to formulations that contain living organisms or their derivatives in a solid form. These formulations are designed for various applications, including agriculture, environmental remediation, and biotechnology. Unlike liquid formulations, which are in a liquid medium, solid bioformulations provide a different matrix or carrier for the organisms. The composition and formulation process may vary based on the specific application, target organisms, and formulation technology used. Factors like compatibility, viability, and compatibility with the carrier or matrix material need to be considered during the development and production of solid bioformulations. Solid bioformulations offer advantages like improved stability and shelf life protection for the organisms from environmental stresses, allowing for easier storage and transportation and providing controlled release of the organisms, prolonging their activity and efficacy. Solid bioformulations can be classified into several categories based on their composition and purpose.

Solid carrier based bioformulations: In this type of formulation, the living organisms are immobilized or embedded within a solid carrier material. The carrier provides physical support, protection, and nutrients for the organisms. Commercially used solid carriers are peat, vermiculite, perlite, clay, or compost. These are used for the application of biofertilizers, biocontrol agents, and bioremediation.

Pellets or Granules: These formulations are typically produced by blending the living organisms with inert solid materials and binders, and then granulating or pelletizing them into a solid form. These provide a controlled release of the organisms and allow for easier application in agriculture like biofertilizers.

Capsules or Tablets: In this type, the living organisms or their derivatives are compressed into tablet or capsule form using suitable inert materials and binders. By offering convenient handling and precise dosing, these are used in applications such as biocontrol agents or probiotics, where the organisms need to be protected during storage and transportation and delivered in a controlled manner.

Powders: Solid bioformulations can also be in the form of finely ground powders. The organisms or their derivatives are typically dried and ground into a powder, which can then be mixed with other ingredients or applied directly to the target area. Powders are commonly used for seed treatments, where the organisms are applied to seeds before planting to enhance germination; protection against pathogens, or to provide other benefits.

7.2 Liquid bioformulations

These are the formulations that contain living organisms or their derivatives available in liquid form and are designed for various applications in agriculture for managing different stresses. These formulations typically consist of a liquid medium that provides a suitable environment for the growth and survival of the organisms, along with other additives that enhance their performance. These are easy to handle, can be applied using conventional spraying equipment, and allow better distribution and colonization of the beneficial organisms on plant surfaces or in the target environment. Moreover, the liquid medium can provide nutrients and protect the organisms during storage and application. Specific liquid bioformulations vary depending on the intended application, target organisms, and the specific formulation technology employed. The formulation process may involve selecting appropriate strains, optimizing growth conditions, and adding stabilizers or additives to enhance shelf life and efficacy. Liquid bioformulations can be broadly categorized into two types: microbial bioformulations and biopesticides.

Microbial Bioformulations: These formulations contain beneficial microorganisms, such as bacteria, fungi, or algae, which are used for various purposes. Some common examples include, Biofertilizers: These formulations contain nitrogen-fixing bacteria or other beneficial microorganisms that enhance soil fertility and plant nutrition. They can improve nutrient availability, promote plant growth, and enhance crop yield. Biocontrol agents: These formulations consist of beneficial microorganisms that help control plant diseases and pests. They can suppress the growth of pathogenic microorganisms or insects, providing a natural and environmentally friendly alternative to chemical pesticides. Biostimulants: These formulations contain microorganisms or their metabolites that stimulate plant growth, enhance nutrient uptake, or improve stress tolerance. They can be used to enhance crop productivity and improve plant health. Bioremediation agents: These formulations contain microorganisms capable of degrading or detoxifying pollutants in the environment. They are used for the cleanup of contaminated soils, water bodies, and industrial sites.

Biopesticides: These formulations are specifically designed for pest control and contain natural substances derived from living organisms. They can be based on microorganisms, such as bacteria, viruses, or fungi, or the plant extracts. Biopesticides are considered safer and more environmentally friendly compared to synthetic chemical pesticides.

8. Methods of biological seed coating

Biological seed coating is a technique used to enhance seed performance and protect seeds from various stresses, such as pathogens, pests, and adverse environmental conditions. There are several methods of biological seed coating that can be employed, each with its advantages and applications. The specificity of the method and formulation varies based on the crop, target pests or pathogens, desired outcomes, and the prevailing environmental conditions. These biological seed coatings are not mutually exclusive, but combinations of different coatings can be used to achieve multiple benefits. Biological seed coatings can be classified into several types based on their composition, purpose, and the agents used. Here are some common types of biological seed coatings.

Encapsulation: This method involves encapsulating the seeds with a protective layer made of natural materials, such as clays, polymers, or biodegradable substances. The coating layer acts as a barrier against external factors, such as pathogens and insects, while providing a controlled release of nutrients or bioactive compounds.

Microbial Seed Coating: It involves application of beneficial microorganisms to the seed surface. These microorganisms can include beneficial bacteria, fungi, or mycorrhizal fungi. The coating provides a reservoir of beneficial microbes that can enhance seed germination, nutrient uptake, and overall plant growth. Additionally, these microbes can help suppress the growth of harmful pathogens.

Biopolymer Coating: Biopolymer-based coatings are derived from natural polymers, such as chitosan, alginate, or starch. These coatings can provide protection against pathogens, regulate water absorption, and enhance seed adhesion. Biopolymer coatings are often used to improve seed viability, reduce seed-borne diseases, and promote seedling establishment.

Biopesticide Coating: Biopesticide seed coatings involve applying naturally derived plant extracts or biocontrol agents to the seed surface. These coatings can help protect seeds from pests and diseases, such as insects, nematodes, or fungi. Biopesticide coatings provide an eco-friendly alternative to chemical pesticides while maintaining seed quality and promoting healthy plant growth.

Nutrient Coating: Nutrient seed coatings aim to provide essential nutrients to the germinating seed or seedling. These coatings contain fertilizers, growth-promoting substances, or micronutrients. The coating ensures that the seed has access to necessary nutrients during early growth stages, enhancing germination, early vigor, and establishment.

Hormone-based Coating: The method involves application of plant growth regulators, such as auxins, cytokinins, or gibberellins, to the seed surface. These hormones can influence seed germination, root development, and overall plant growth. Hormone-based coatings are used to enhance seedling vigor, stimulate root growth, and improve stress tolerance.

9. Factors that affect the effectiveness of biological seed coating

The following factors influence the effectiveness of the biological seed coating.

Seed characteristics: The size, shape, and texture of seeds may vary depending on the type of seed. These traits may affect the efficacy of biological coatings adherence and persist on seed surface. Some seeds may have natural structures or coatings that make it easier or hinder the microbes to attach.

Choice of Microorganism: The choice of selecting microorganisms for seed coating is crucial. Factors like microbial strains, its compatibility with specific crop, and the expected benefits (e.g., disease/pest management, nutrient solubilization) should be taken into consideration as varied microbes have their own requirements for growth, survival, and interaction with seed and seedlings.

Colony-Forming Units per milliliter (CFU/ml) or per gram (CFU/g): It allows the quantification of viable microbes and assessment of microbial load, growth, or inhibition in different samples and systems which is important for disease suppression.

Coating formulation: To ensure viability and stability, the composition of the microorganisms along with their formulation is important. The survival and efficacy of these microbes can be affected by the factors such as carrier materials, protective additives, and application techniques. However, optimization of coating formulation is required to provide ambient conditions for the growth and activity of the microbes.

Application technique: The process used for applying biological coatings to seeds has a direct effect on the coating’s coverage, consistency, and adherence. The techniques viz., film coating, slurry coating, or vacuum impregnation can be employed.

Adjuvant used for coating: Bio-friendly polymer and nonionic polymers, biopolymers used as an adjuvant recorded good viability and shelf life of bioagent compared to conventional adjuvants like sugar/jaggery syrup.

Viability and shelf life: The ability of a bioagent to survive and maintain its effectiveness over time when stored under particular conditions is referred to as its viability and shelf life. The bioagent must be viable and have a long shelf life in order to be useful across a range of applications.

Environmental conditions: Environmental factors, including temperature, humidity, and light exposure, can influence the survival and activity of the microorganisms on the seed surface. Some microorganisms may have specific temperature or moisture requirements for optimal performance. High temperatures or prolonged exposure to UV light can negatively impact the viability and efficacy of the microorganisms.

Seed storage and handling: Proper seed storage and handling practices are essential to maintain the viability of the biological coating. Storage conditions, such as temperature, moisture, and duration, can affect the survival of the microorganisms. It is important to follow recommended storage guidelines to preserve the efficacy of the biological coating until the seeds are planted.

Interactions with other seed treatments: If other seed treatments, such as fungicides or insecticides, are applied in conjunction with biological seed coating, compatibility and potential interactions should be considered. Some chemical treatments may adversely affect the survival or activity of the microorganisms, leading to reduced efficacy of the biological coating. Considering these factors, the seed coating process can be optimized accordingly, and the effectiveness can be maximized, leading to the improvement of seed quality and crop performance.

10. Several factors can influence the viability and shelf life of a bioagent

It is significant to remember that a bioagent’s viability and shelf life might change based on the particular organism, formulation, and storage conditions. Manufacturers often include guidelines and suggestions for storage conditions, shelf life, and handling procedures. Following these recommendations will assist the bioagent to remain as viable and effective as possible throughout its shelf life.

Storage Conditions: The viability and shelf life are greatly influenced by the storage conditions, which include temperature, humidity, and light exposure. The storage conditions for each bioagent should be specified based on their specific requirements. For instance, some bioagents can be stored at ambient temperature, while others may need to be refrigerated. It is crucial to adhere to the manufacturer’s prescribed storage recommendations.

Formulation and Packaging: The formulation and packaging of the bioagent can impact its viability and shelf life, wherein the selection of carrier materials, stabilizers, and protective additives can help in enhancing the stability and longevity of the bioagent. Further, an airtight and moisture-resistant container prevents contamination and moisture exchange, which may affect the viability of the bioagent.

Strain Selection: It is important to select stable strains or isolates of a bioagent as some of them may have better survival and stability potential and more suitable for extended shelf life. Screening and selection of strains help in identifying the strains with preferred characteristics.

Adjuvant used for coating: Bio-friendly polymer not only acts as a good binder but also provides nutrients required for the survival of microorganisms on the coated seed surface compared to sugar/jaggery syrup.

Quality Control: In order to ensure bioagent viability and shelf life, it is much essential to follow strict quality control measures during production and formulation, which helps in assessment of viability and enumerating the microbes to ensure consistent quality of a product. Further, batch testing and monitoring at regular intervals are needed to identify any potential deviations or reduction in viability.

Shelf Life Testing: Stability test should be conducted to evaluate the viability and efficacy of the bioagent over a period of time by subjecting the bioagent to accelerate aging or ambient storage conditions and assessing its viability and efficacy at periodic intervals. The test helps in determining the expiry period of the product.

11. Compatibility studies for biological seed coatings

Studies on the compatibility between the biological agents used in the formulation of biological seed coatings and the other components of the coating system have to be performed to ensure that the biological agents remain effective and efficient and do not adversely affect the coating or other additives. Key components to consider when executing compatibility studies for biological seed coatings are:

Compatibility with Coating Materials: Biological agents have to be tested for their compatibility with coating materials, such as binders, adhesives, polymers, film-forming agents, and so on, where they do not interfere with the coating process, adhesion to the seed surface, as well as physical integrity of the coating. Other additives like colorants, surfactants, or nutrients that are included in the seed coating formulations should be evaluated for their compatibility with biological agents, where the additives do not have negative impact on viability or efficacy of biological agents. These studies can be carried out by following poison food technique for fungi and zone of inhibition technique for bacteria. In agricultural or horticultural crops, to ensure the successful integration of the biological agents into the coating formulation, the compatibility studies help in the optimization of the formulation and the performance of coated seeds to confer desired benefits.

Compatibility with other bioagents: For the development of bioagents consortia, biological agents have to be tested for their compatibility with each other with the help of dual culture technique.

Viability Assessment: The effect of the coating materials on the viability of the biological agents has to be assessed by determining the Colony Forming Units (CFU) to assess the survival and growth of microbe after subjecting to the coating process.

Physical and Chemical Stability: The biological agents have to be assessed for their physical as well as chemical stability to observe any deviations in pH, temperature, or moisture content, which affect the viability of microbes. Performing long-term stability studies influences the shelf life and storage conditions of coated seeds.

Efficacy Evaluation: Finally, after seed coating, the effectiveness of biological agents and further the ability of the coated seeds to have desired biological benefits like improved germination, plant growth promotion, disease or pest control should be assessed. The efficacy of bioagents can be tested both in the laboratory and field conditions.

12. Materials required for biological seed coating

The specific material requirements will be varied and depend on target crop, bioagent strains, coating formulation, and desired outcomes. For effective application of biological agents onto the seed surface, the following are the commonly used materials in biological seed coating:

Beneficial Microorganisms: Selection of potential strains of beneficial microorganisms (bacteria, fungi, or mycorrhizal fungi) in pure form or commercial products from specialized suppliers. The use of effective native isolates will give better protection against disease causing pathogens.

Carrier Materials: Carrier Materials: Talc is a commonly used carrier because of its fine texture, absorption capacity, and ability to aid in the equal dispersion of microorganisms on the seeds. This helps to offer a suitable medium for the beneficial microbes to adhere to the seed surface. Clays, like kaolin or bentonite, offer the microorganisms a moderate amount of adhesion as well as protection. Vermiculite is a type of mineral that can hold moisture and create an ideal habitat for the development of microorganisms. Biopolymers: Chitosan, alginate, or starch are examples of biodegradable polymers that can be utilised to enhance adhesion, microorganism protection, and controlled nutrient release.

Adhesive Substances/Adjuvants: Plant-based gums, gelatinous solutions, or biodegradable polymers like starch or cellulose are used to increase the adherence of the carrier and microorganisms to the seed surface. These increase stickiness and encourage the adhesion of the carrier material to the seed.

Protective Agents: To enhance seed protection, protective agents may be added in the coating formulation, such as antioxidants like ascorbic acid or vitamin E, to provide protection to the microorganisms and seeds from oxidative stress during storage or handling. Natural or synthetic compounds having antifungal or antibacterial properties can be included to the coating formulation to protect against seed-borne pathogens.

Proper packaging materials (moisture-proof) and packing method is needed to maintain seed viability and integrity of the coating.

13. Dosages of biological seed coating

Although dosages for biological seed coating vary depending on the product, crop, seed size, and so forth, it is necessary to account for the amount and active ingredients applied to the seed. Therefore, to determine the accurate dosages for any particular application, valuable suggestions have to be taken from product manufacturer, agricultural extension services, or agronomists. The following are some points to be considered for fixing dosages of biological seed coating:

Recommended Application Rates: For the particular product, manufacturers frequently offer recommended application rates or instructions. Depending on the target crop, the type of seed, and the desired results, these guidelines may recommend a range of treatment rates. To ensure proper dose, it is essential to carefully read and adhere to these recommendations.

Seed Size and Weight: The dosage when coated on the seed can influence the size and weight of the seeds. Generally lower dosage is required for the smaller seeds over the larger seeds to achieve maximum coverage and adherence of the coating. Uniform application of seed coatings should be done to have consistent results.

Concentration of Active Ingredients: The dosage can also be affected by the concentration of active components, such as beneficial microbes or bioactive substances, in the composition of the seed coating. The suggested dosage will depend on the exact formulation because various products may have variable concentrations.

Seed Coating Method: The dosage of application may vary depending on the method by which the seeds are coated. In order to ensure sufficient coverage and adherence of the coating to the seed surface, the dosage may need to be adjusted for various coating processes, such as slurry coating, dry coating, or film coating.

Seed Treatment Equipment: The dose of the biological seed coating can vary depending on the type of seed treatment equipment being utilized. In order to provide precise and constant application rates, manufacturers may offer guidelines for equipment calibration and settings.

14. Process of biological seed coating

In order to ensure that the biological agents are applied accurately and that the seeds are properly treated, the biological seed coating process entails several steps. It is important to keep in consideration that the precise procedures and methods may change based on the biological agents, seed coating components, and equipment utilized. Additionally, the seed coating procedure may be influenced by factors including seed species, desired results, and regulatory considerations. The common procedure includes:

Selection of Biological agents: Select potential beneficial microbes such as bacteria, fungi, mycorrhizal fungi, or other PGPRs for seed coating that offer protection against pathogens or enhance nutrient uptake.

Preparation of Biological agents: Culture the bioagents in a suitable growth medium under controlled conditions to have a sufficient spore load/population for seed coating.

Seed Treatment: Prior to treatment, the seeds should be cleaned, sorted, and evaluated for quality. Remove any contaminated or unhealthy seeds. If necessary, treatments like applying fungicides or insecticides can be done at this stage.

Coating Formulation: By combining the biological agents with a carrier substance, prepare the coating formulation. The carrier material might be an adhesive substance like biopolymers or gelatinous solutions, or it can be a powdered material like talc, clay, or vermiculite. The biological agents should adhere to the seed surface, and formulation should be distributed uniformly.

Seed Coating Application: Apply the coating formulation on to the seeds, which can be done either manually or with specialized seed coating tools. In order to obtain a consistent coating, the seeds are often tumbled or rotated in a drum, while the coating composition is sprayed or applied evenly.

Drying and Curing: After application of coating, to achieve efficient coating adhesion and to avoid seed clumping or sticking, the coated seeds must be dried and cured. This can be accomplished by distributing the coated seeds in a well-ventilated area or by employing temperature and humidity-controlled drying chambers.

Quality Control and Packaging: Following drying and curing, the coated seeds are subjected to quality control inspections to make sure the coating application is uniform and meets the standards. After being packaged in appropriate containers with the correct labeling and storage conditions, the coated seeds are stored to maintain seed viability advanced innovations in biological seed coating for tomato are mentioned in Table 2.

Crop	Beneficial organism	Method	Mode of action	Reference
Tomato	Trichoderma harzianum	Seed treatment	Trichoderma hyphae completely engulfed the hyphae of R. solani by coiling and hooking. Decreased 49.5 and 64.33% of pre-emergence damping-off disease caused by P. infestans and R. solani, respectively. Trichoderma treatments had a positive effect on growth parameters compared to control.	[65]
Tomato	Five biocontrol bacteria (Bacillus amyloliquefaciens (Ba), Bacillus subtilis (Bs wy-1), Bacillus subtilis (WXCDD105), Pseudomonas fluorescens (WXCDD51), and Bacillus velezensis (WZ-37)	Mixed with auxiliary factors (inactive components of seed-coating agent) after fermentation	The seedling mortality rate due to Pythium aphanidermatum was 26.7% lower than that of the sterile water control and 20% lower than that of carbendazim.; The seedling mortality rate caused by Fusarium spp. was 44.31% lower than that of the control and 22.36% lower than that of carbendazim.	[66]
Tomato	Bacillus siamensis CU-XJ-9	—	Produced nodules and destroyed the mycelial structure of Fusarium graminearum through the production of lipopeptide antibiotics.	[67]
Pigeonpea	Trichoderma viride, Pseudomonas fluorescens, Bacillus subtilis	Seed Coating	Improved seed germination in biologically coated seed	[68]
Tomato	Endophytic bacteria (SuRW02)	Seed coating	Endophytic bacteria recorded 38% incidence of Fusarium wilt and disease severity indices of 0.37. The uncoated seeds and seed coating without endophytic bacteria showed disease incidences of 70 and 50% and disease severity indices of 2.00 and 1.25, respectively. It further promoted tomato plant growth and quality of tomato production.	[69]
Tomato	Trichoderma pseudokoningii	Seed biopriming with vermiwash combination	Under heat-stress conditions, root biomass increased.	[70]
Tomato	Bacillus subtilis subsp. subtilis, and T. harzianum	—	Significantly enhanced tomato plant growth and immunity when used against P. infestans.	[71]
Tomato	Four Trichoderma isolates	Seed treatment	Depending on the Trichoderma isolate, there was a significant rise in germination percentage and a reduction in the incidence of pre-emergence damping-off with biocontrol efficiency against R. solani ranging from 20.66 to 39.23% and Pythium spp. from 32.39 to 64.46%. However, isolate T. harzianum has improved plant height, number of leaves and flowers per plant, dry and fresh weight, root length and yield	[72]
Chili	T. harzianum	Seed treatment	Proved effective in controlling damping-off disease caused by Pythium aphanidermatum	[73]
Tomato	T. harzianum	Seed treatment	Overall enhancement of plant growth was observed when used against Pythium ultimum and Phytophthora capsica.	[74]
Pigeonpea	Trichoderma viride, Pseudomonas fluorescens, Bacillus subtilis, Rhizobium spp.	Seed treatment	Improved seed germination in biologically coated pigeonpea	[39]
Tomato	T. harzianum	Seed treatment	Isolate Th-Sks showed 79.47% growth inhibition of Phytophthora infestans with the suppression efficacy of 91–100% in field and promoted plant height and fruit yield	[75]
Tomato	Isolates of T. asperellum TRC 900 (10^6 spores/ml); and B. subtilis BS 01 (10^6; CFU/ml)	Three grams of wet seeds were mixed either with B. subtilis or with T. asperellum; suspensions followed by air drying at 25°C for 24 h.	Under heavy disease pressure, coated seed showed lower percentage of pre-emergence damping-off. Combination of seed coating and fertilizer application (NPK fertilizer of 400 ppm) accelerated the growth of the seedlings. Among the two bioagents, B. subtilis was highly efficient in controlling damping-off caused by P. aphanidermatum compared to T. asperellum.	[76]
Tomato	Trichoderma spp.	Different substrates amended with Trichoderma	Noticeable reduction of damping-off caused by R. solani in tomato was seen.	[77]
Tomato	T. harzianum	Foliar application of T. harzianum spores	Inhibited 67.78% incidence of Alternaria leaf blight	[78]
Tomato	Endophytic actinomycetes (Strains CA-2 and AA-2 related to Streptomyces mutabilis NBRC 12800 T and Streptomyces cyaneofuscatus; JCM 4364 T)	Seed coating	Reduced the severity of damping-off of tomato seedlings and showed a substantial rise in the seedling fresh weight, seedling length and root length of the treated seedlings compared to the control.	[79]
Tomato	Bacillus spp. and Pseudomonas spp. (PGPR)	Seed coating	Inhibited the growth of the Fusarium spp., a wilt pathogen, by making use of mechanisms such as indole acetic acid production, siderophore production, phosphate solublilization, systemic resistance induction and production of antifungal volatile componuds.	[80]
Tomato and chili seedlings	Antagonistic Streptomyces rubrolavendulae S4	Growing of seedlings in P. infestans artificially inoculated peat moss	Significant increase in the survival rates of colonized tomato and chili seedlings, from 51.42 to 88.57% and 34.10 to 76.71%, respectively.	[81]
Tomato	Lactic acid bacteria (LAB), isolated from milk and yoghurt	Seed treatment or soil drench	Acted as plant growth promoting bacteria and biocontrol agent against some phytopathogenic fungi such as Fusarium oxysporum, under in vivo tests	[82]
Tomato	Bacillus subtilis (GIBC-Jamog) and Burkholderia cepacia (TEPF-Sungal) and PGPR strain mixtures, S2BC-1 (B. subtilis) + GIBC-Jamog (B. subtilis) and S2BC-2; (Bacillus atrophaeus) + TEPF-Sungal (Burkholderia cepacia)	Seed bacterization and; soil application of S2BC-1 + GIBC-Jamog challenge-inoculated with F. oxysporum f.sp. lycopersici.	Significant decrease in the incidence of vascular wilt caused by the fungus Fusarium oxysporum f.sp. lycopersici and localized induced systemic resistance (ISR) compared to non-bacterized seed.; .	[83]
Chili, Tomato and brinjal	P. fluorescens	Biopriming	Stimulated the germination of seeds better than some fungal biopriming agents viz., T. viride AN-10 and T. harzianum AN-13	[84]
Tomato	T. harzianum Rifai strain T-22	—	Alleviated abiotic stress tolerance factors like osmosis, salinity, chilling, and high temperature.	[85]
Tomato	B. brevis	—	Potential biological control agent that reduced the impact of Fusarium oxysporum f.sp. lycopersici	[86]
Tomato	T. harzianum and fluorescent; Pseudomonas	seed bio-priming	Increased seed germination (22–48%), decreased germination time (2.0–2.5 days), and decreased incidence of wilt in pots and fields. In pots and the field, respectively, the combination of fluorescent Pseudomonas, T. harzianum, and arbuscular mycorrhizal fungus (AMF) recorded superior control than uninoculated treatment. The yield was also increased by 20% by the combination treatments. In all treatments, the addition of cow dung compost (CDC) further decreased the disease and improved yield in all treatments.	[87]
Tomato	Trichoderma spp.	Seed treatment	In the presence of abiotic stress oxidative damage conditions, Trichoderma treatment guarantees a high speed and more uniform germination through physiological protection and decreased accumulation of lipid peroxides.	[88]
Tomato	T. harzianum and P. fluorescens	Seed coating of inoculum	Reduced the mean germination time to less than 2.5 days and increased the germination rate to more than 48%. In comparison to single-isolates, inoculant combinations were more successful.	[89]
Carrot and onion	T. viride, Pseudomonas fluorescens, Pseudomonas chlororaphis, Clonostachys rosea, and Pseudomonas chlororaphis	Seed priming	Improved emergence and a better emergence time under glasshouse condition.	[90]
Tomato	T. harzianum	Seed coating	Recorded high seedling emergence and seedling shoot fresh weight.	[91]
Tomato	Pseudomonas fluorescens (10^8 cfu/ml)	Biological seed treatment- Slurry seed treatment at the rate of 10 g/ kg seeds followed by air drying for 12 h.	Improved seed quality and significantly reduced Xanthomonas vesicatoriacausing bacterial spot disease incidence in fields	[92]
Tomato	T. harzianum	Plants treatment	Showed reduction in damping-off and root rot diseases. Gave high fruit yields.	[93, 94]
Tomato	Trichoderma spp.	Seed treatment	Considerable yield increase was noticed in the plant seeds when pre-treated with Trichoderma spore suspension.	[35, 94]
Tomato	Trichoderma spp.	Biopriming of seeds with Trichoderma formulations before sowing/planting	The ability of isolates of T. harzianum to produce phytohormones such auxins, gibberellins, and cytokinins, vitamins, and solubilizing minerals contributed to the promotion of tomato growth parameters besides, their role in direct inhibition of pathogen growth.	[93]
Tomato	B. subtilis and B. lentimorbus	—	Potential to be used as biocontrol agents against R. solani	[95]
Tomato	Pseudomonas aureofaciens AB254 (10^5 bacteria cfu / seed.)	Seeds were bio-osmoprimed by soaking in aerated −0.8 MPa NaNO3 for 4 days at which time a mixture of nutrient broth, polyalkylene glycol, and bacterial stock were added. Seeds were then hydrated for an additional 3 days	At a slightly slower rate, bio-osmopriming also offered defense against the damping-off fungi Pythium ultimum. This method also increases the possibility of the seed lot establishing a healthy stand.	[96]
Tomato	Pseudomonas aureofaciens AB254 (10^8 bacteria cfu / seed.)	Seed coating with AB254	AB254 coatings protected tomato seeds from damping-off fungi Pythium ultimum infection equally as the fungicide, Metalaxyl.	[96, 97]
Tomato	T. harzianum	Seed coating or in wheat-bran/peat (1:1,v/v) rooting mixture	Fusarium oxysporum f.sp. radicis-lycopersici was completely eradicated from the rhizosphere root zone due to the proliferation of T. harzianum and resulted in 26.2% increase in tomato yield over the control.	[98]

Table 2.

Advanced innovations in biological seed coating in tomato (table is extrapolated from other works).

15. Mode of action of biological seed coating

Biological seed coatings have different modes of action. Depending on the microorganisms employed and their interaction with the seed and the surrounding environment, the precise method of action can change. Here are a few typical biological seed-coating modes of action:

Biological Control: The beneficial microbes used in seed coatings show antagonistic properties and combat the plant pathogens through various mechanisms like antibiosis [47], competition [48], and parasitism, apart from inducing systemic resistance in host plants [52, 67, 75, 86, 95].

Disease Suppression: Many of the microbes used in seed coating technique protect the seeds as well as seedlings from various seed and soil-borne infections by producing antibiotics or other antimicrobial compounds that affect the growth of pathogens [65]. In addition to competing for resources, they colonise the rhizosphere, which causes host plants to develop systemic resistance and so protect themselves from plant infections [73, 79, 94].

Nutrient Solubilization and Enhancement: Some microorganisms have the capacity to solubilize nutrients. Nutrients like phosphorus can be solubilized by specific microbes, which increase their availability to plants [93]. They synthesize the phosphatases and other enzymes that convert complex nutrient forms into simpler forms that plants can readily absorb. This promotes plant growth and development and improves the efficiency of nutrient uptake.

Enhanced Germination and Seedling Establishment: Microorganisms found in seed coatings can promote seed germination and increase the vigor of seedlings [39, 68]. These microbes may produce enzymes that stimulate root and shoot growth or break down seed dormancy. As a result, seedlings emerge more quickly and uniformly, enhancing the crop establishment [81, 89, 90, 92].

Plant Growth Promotion: Beneficial microbes used in seed coatings enhance plant growth-promoting substances like phytohormones, which can directly encourage the plant growth (65, 71, 74 82). However, they indirectly aid in increasing nutrient availability, promoting root development, and enhancing physiological plant processes leading to health plant growth [94, 98].

Environmental Stress Tolerance: Some microorganisms found in seed coatings can increase plants’ resistance to environmental challenges like drought, salt, and severe temperatures [70, 71, 83]. They could synthesize stress-responsive compounds, such as osmoprotectants or heat-shock proteins, which aid plants in surviving adverse conditions and increasing their yield [85, 88].

16. Precautions for biological seed coating

Certain safety guidelines should be followed while utilizing biological seed coatings to ensure correct handling, application, and security. However, these precautions are only general recommendations, and they may change depending on the product, formulation, and regional regulations. Therefore, always read the product label and consult the manufacturer or industry professionals regarding specific usage guidelines and safety measures before using of the biological seed coating product. When handling biological seed coatings, the following general safety measures have to be taken:

Follow Product Instructions: Read the manufacturer’s instructions, suggestions, and safety data sheets that are provided with the biological seed coating product carefully, and then follow them. Follow the manufacturer’s recommended dosage, application guidelines, and safety instructions.

Personal Protective Equipment (PPE): As suggested by the product’s manufacturer, wear proper protective equipment, such as gloves, protective clothes, goggles, and respiratory protection. Refer to the product label for detailed instructions since PPE requirements can vary depending on the particular product and application method.

Storage and Handling: The biological seed coating materials should be kept out of direct sunlight and high temperatures in a cool, dry location. Observe any special storage instructions that the manufacturer may have provided. Be cautious when handling the items to prevent spills, leaks, and contact with the skin, eyes, or clothing.

Mixing and Application: The biological seed coating product should be prepared and mixed in accordance with the manufacturer’s instructions. Use the right equipment and adhere to the suggested application techniques. To reduce the risk of exposure or inhalation, avoid creating too much dust or aerosol during mixing and application.

Environmental Considerations: When applying biological seed coatings, adhere to the appropriate environmental rules and regulations. Applying the coatings in areas with possible environmental hazards, such as those close to water bodies or delicate habitats, is not advised. Precautions should be taken to prevent water sources from being contaminated, including adhering to buffer zone restrictions.

Seed Quality: Make sure that the seeds being coated are of high quality and not contaminated by insect or pathogens, or other pollutants. Poor quality seeds may increase risks or have an adverse influence on the seed coating’s efficiency.

Disposal: Using correct waste disposal techniques to dispose of any empty containers, unused product, or waste materials in accordance with local regulations taking to consideration their impact on the environment.

Record Keeping: Ensure that all information regarding the products used, application rates, dates, and any observations or results is accurate. This knowledge may be useful for future research, assessment, or troubleshooting.

17. Future challenges

Manipulation or improvement of the PGPR strains for overall health of the crop will determine their future. However, genetically engineering of the PGPR to obtain desired effects and employing nano-fertilizers or/and pesticides combined with isolated effector molecules from the PGPRs instead of the complete organism are the few approaches that can be used to accomplish the aspects. Further, the technology or/and the technological improvements in this area have yet to be demonstrated, assessed, and standardized, and they should also be economically viable.

18. Conclusion

It is to conclude that the biological seed coating offers environmentally friendly and sustainable approach that provides efficient protection against seed and soil-borne pathogens, seed quality improvement, and crop productivity enhancement by reducing reliance on harmful synthetic inputs of agriculture. It is in line with the principles of sustainable farming practices, promotes ecological balance, and supports the safe and healthy food production for a growing population.