Nitrogen is the most critical nutrient for plant growth, and perhaps the most recognizable example of biofertility inoculants are the rhizobia which fix atmospheric nitrogen in nodules of legume crops. This diverse group of bacteria comprises some of the most intensely investigated microbes owing to their value as inoculants. Despite their taxonomic diversity, all rhizobia establish symbiotic interactions with their host plant via highly conserved mechanisms which have been reviewed extensively (Alexander, 1984; Weidner et al., 2003; Zahran, 2009; Terpolilli et al., 2012). Legume crops are grown on an estimated 250 million hectares globally and fix roughly 90 million metric tons of atmospheric nitrogen annually (Zahran, 2009).

Effective rhizobial products exhibit high rates of nitrogen fixation and compete successfully with less efficient indigenous rhizobia populations to colonize and form nodules on target host plants. Successful commercial production of rhizobia required the ability to produce the organisms in large quantities and enable a long-term shelf life. Unfortunately, many microbial products fall short in the latter specification leading to overall poor performance in the field. In the 1980s and 1990s many rhizobial products showed poor efficacy (Catroux et al., 2001). However, over the past decade both quality standards and performance of these products have improved substantially, and several marketed products have been shown to affect consistent improvements in yields of legume crops. Nitrogen-fixing products sold today contain substantially higher numbers of viable organisms per gram than those from earlier decades. Additionally, improved product formulations have resulted in enhanced stability (Grooms, 2008). In tests with inoculated soybeans, Beuerlein (2008) reported yield improvements averaging approximately 120 kg per hectare.

Soybeans contain 37–45% protein by weight, and thus, a 3600 kg ha^-1 crop requires 136 kg of nitrogen (Beuerlein, 2008). To illustrate the impact of rhizobial products on soybean yields, products sold by the Monsanto BioAg Alliance (Optimize^®) (Monsanto BioAg Alliance, 2015e), BASF (Vault^®), ABM (Excalibre^TM), and MycoGold^TM are discussed. In addition to live Bradyrhizobium cells, Optimize^® for soybeans contains lipochitooligosaccharide, a molecule that enhances the soil microbial environment¹ Seeds treated with Optimize^® consistently show an increase in yield over untreated controls (Figure 1). Similarly, Vault^® is a seed treatment consisting of Bradyrhizobium and a patented rhizobial enhancer (Basf-Corporation, 2015). ExcalibreSA^TM is a blend of Bradyrhizobia², and MycoGold^TM blends Bradyrhizobium with biostimulants and other microbes³ The use of bioinoculants on soybean crops consistently provides a 4:1 return on investment.

In addition to the nodule-forming rhizobia which establish nitrogen-fixing symbioses in legumes, there are numerous species of non-legume nitrogen fixing bacteria that associate with agriculturally important crops (Rai, 2006). Among these, members of the genera Azospirillum MicroAZ-ST^TM (TerraMax⁴), and Mazospirflo-2 (Soilgro; Owen et al., 2015), Azotobacter Bio-N^TM (Agriculture Solutions⁵), and Gluconacetobacter have attracted interest, because they are root-colonizing and exhibit the potential to transfer fixed nitrogen to the plants with which they associate. Non-legume nitrogen fixing bacteria have been shown to increase yield of various crops including sunflower, carrot, oak, sugar beet, sugar cane, tomato, eggplant, pepper, cotton, wheat, and rice (Bashan et al., 1988; Bashan and Holguin, 1997). In a review summarizing 20 years of global field trials, Okon and Labandera-Gonzales (1994) reported that in 60–70% of the trials, inoculation with various Azospirillum strains increased crop yields by 5–30%. Another extensive, multi-year study conducted by Diaz-Zorita et al. (2012) showed that on-seed inoculation increased wheat and maize yields by 244 kg ha^-1 (3.9 bu ac^-1) and 514 kg ha^-1 (8.2 bu ac^-1), respectively. In addition to nitrogen fixation, some Azospirillum species are capable of producing plant growth-promoting compounds which may play a role in their mode of action (Okon et al., 2015). Non-leguminous nitrogen fixing bacteria also manifest other plant-beneficial traits such as remediation of soils polluted with heavy metals (Ullah et al., 2015) and confer enhanced tolerance in plants to abiotic stresses such as drought (Vargas et al., 2014).

Compared with other soil nutrients, phosphorus is the least mobile and is usually in a relatively unavailable form for plant uptake. Next to nitrogen, this nutrient is the second most important nutrient in crop production and is traditionally applied in the form of chemical fertilizers or manure. The world’s supply of rock phosphate is expected to be largely depleted in the next few decades (Gilbert, 2009; Scholz et al., 2013). With China, India, and the US as the major users of rock phosphate and 70% of known deposits located in China, Russia, Morocco, and the US, the long term sustainability of current phosphate resources is debated. To ensure the most efficient use of limited supplies of rock phosphate fertilizer and circumvent future shortages, phosphorus-solubilizing microorganisms have been developed to enhance the nutrition of crops in a sustainable manner.

Ironically, the total amount of phosphorus in soils may be high, but it is usually present in forms that are unavailable for plant growth. These comprise both organic and inorganic pools, of which 20–80% can be found in organic forms that include phytic acid (inositol hexaphosphate) as a major component (Richardson, 1994). The largest fraction of inorganic phosphate in soil resides in complexes with metals (particularly Ca, Al, and Fe) (Richardson, 2001). Soil microbes that liberate phosphate from organic and inorganic pools have been promoted as products that effectively mobilize phosphate from poorly available sources in soil and reduce the application of rock phosphate fertilizer. Products such as these are expected to show rapid commercial growth over the next few years. While the genetic and biochemical components underlying the mechanisms of phosphate-liberation by these organisms have not been as extensively studied as nitrogen fixation, excretion of organic acids and synthesis of phosphate-scavenging enzymes such as phytases have been implicated in their modes of action (Richardson, 2001).

Pools of insoluble phosphate in metal complexes can be made available to plants through the action of phosphorus-solubilizing microorganisms. Improved crop yields resulting from the application of phosphorus-solubilizing organisms in the field have been reported (Pradhan and Sukla, 2005), notably Bacillus (Symbion-P^®) and Pseudomonas among bacterial genera, and Aspergillus and Penicillium are among the most important fungal taxa. In comparing characteristics of phosphorus-solubilizing bacteria and fungi, it has been reported that fungi exhibit greater solubilizing activity than bacteria (Nahas, 1996). Penicillium bilaiae is a fungus present in the commercial product Jumpstart^® marketed by the Monsanto BioAg Alliance (2015a). The organism solubilizes soil phosphorus by a mechanism that involves secretion of citric and oxalic acids (Cunningham and Kuiack, 1992). A recent publication by Leggett et al. (2015) summarized the findings of a large multi-year field study to assess the yield responses of maize to inoculation with JumpStart^®. Rigorous statistical analyses of both large and small test plots revealed significant yield increases in 66 of 92 (72%) small plots and 295 of 369 (80%) large plots (Table 1). These results strongly suggest a significant impact on maize yields as a result of the fungus P. bilaiae. The lack of successful commercial phosphate-solubilizing inoculants has been noted (Leggett et al., 2001) and attributed to plant or environmental incompatibility.

Another group of phosphate solubilizing microorganisms are arbuscular mycorrhizal fungi (AMF) that are able to form a network of hyphae that interact with the plant roots to improve nutrient transport and protect the plant against pathogens and some forms of abiotic stress (Porcel et al., 2012; Hodge and Storer, 2015). Most of the vascular plants on Earth form an association with AMF (Smith and Read, 2008); they are ubiquitous and ecologically important for soil health. Within the AMF, the most widely used products in agriculture usually belong to the phylum Glomeromycota (Owen et al., 2015) and have been shown to increase P uptake. Some of the examples of AMF products include Mycormax^® (JH Biotech⁶), BEI (BioOrganics^TM7), BioGrow Endo (Mycorrhizal Applications⁸), and VAM (Microbesmart⁹).

Interestingly, a few commercial products have emerged that take advantage of combining different biofertility products. One such product, marketed under the trade name QuickRoots^®, is sold by the Monsanto BioAg Alliance (2015b). This product contains a patented combination of the Bacillus amyloliquefaciens and the filamentous fungus Trichoderma virens (Monsanto BioAg Alliance, 2015c,d). Both of these organisms are known to liberate bound phosphate making this nutrient more available to plant roots (Fan et al., 2011; Akladious and Abbas, 2012; Molla et al., 2012; Lamdan et al., 2015), and the combination purportedly imparts increased availability of nitrogen, phosphorus and potassium in soil resulting in expanded root volume for enhanced yield potential¹⁰ Field trial data with QuickRoots^® applied to corn shows a positive yield ranging from 220 to 500 kg ha^-1 increase representing a 2:1 to 5:1 return on investment (Figure 2)^{numfont 10}. Lastly, the combination of these two organisms may also enhance favorable interactions of plant roots with mycorrhizal fungi in the soil (Johnson, 2013, 2015). Other examples of mixed products include Excalibre-SA (ABM), which combines Trichoderma with Bradyrhizobium for soy¹¹, and BioGrow Endo (Mycorrhizal Applications) combines AMF and Trichoderma¹²

Biocontrol agents are broadly classified as preparations either derived-from or containing living microorganisms that can prevent or suppress pests like pathogens, insects, and weeds. Biocontrol agents can include living microbes (bacteria, fungi, nematodes, viruses and protozoa), bioactive compounds such as secondary metabolites (e.g., spinosads and avermectins), or naturally derived material such as plant extracts (Kiewnick, 2007; van Lenteren, 2012). Pest damage prevention by biocontrol agents is based on several mechanisms that may involve antibiosis, competition for space and nutrients, mycoparasitism, enzymatic activity, and induced resistance (Lo, 1998). These modes of action are certainly not exclusive, and biocontrol agents likely enlist a combination of activities when counteracting disease.

As previously mentioned, industrial application of biocontrol microbes will require a deeper understanding of the biology of the microbe, the targeted pest or pathogen, and interactions with host plants, other microbes, and the environment. Drivers of microbe communities in the rhizosphere, for example, involve soil type and plant genotype (Berg and Smalla, 2009; de Bruijn, 2013), whereas the phyllosphere microbiome is influenced by plant genotype and environmental factors like humidity, ultraviolet light, and geographic location (Vorholt, 2012; Rastogi et al., 2013). Understanding these ecological differences is critical when making decisions about product development and commercial application. In an illustration of abiotic effects, biocontrol efficacy by nonpathogenic Fusarium oxysporum was significantly affected by both temperature and light (Larkin and Fravel, 2002). In another example of biological complexity, Erlacher et al. (2014) found that shifts in lettuce microbe communities caused by pathogen infection (Rhizoctonia solani) were offset by the biocontrol agent Bacillus amyloliquefaciens FZB42. Such selective compensation of pathogen impact by a biocontrol strain suggests a novel mode of action and highlights the complexity of biocontrol within a plant–microbe ecosystem. Understanding how biocontrol microorganisms interact with one another represents another biological challenge for product development. Co-inoculation of Trichoderma viride strain GB7 and Serratia plymuthica strain 3Re4-18 resulted in greater biocontrol efficacy against R. solani in lettuce, compared to application of single strains (Grosch et al., 2012). However, combined biocontrol application also had a more pronounced impact on the microbial community structure at large (Grosch et al., 2012). These studies highlight the complex and fluid interactions between plant, pathogen, biocontrol agent, microbe community, and the environment. To commercialize effective biocontrol microbes as products, industries will need to invest in fundamental and early development research surrounding these biological questions. This will require deeper partnerships within industry as well as greater communication with academic (public and private) and government research organizations.

Commercialization of a successful biocontrol product ultimately depends on the availability and isolation of candidate microbes. This screening process involves isolation from a particular environment and early trials to characterize a microbe’s biocontrol capability. While no single screening method is optimal for all biocontrol endeavors, a logical strategy should be followed based upon the pathosystem (plant-pathogen-environment) of interest (Fravel, 2005). For example, finding biocontrol agents against foliar-specific pathogens would likely require screening microbes that can colonize the phyllosphere. Culturing phyllosphere-associated microbes from tomato (Enya et al., 2007) and wheat (Yoshida et al., 2012) has resulted in the identification of potential biocontrol microorganisms for foliar pathogens. Likewise, screening for biocontrol against post-harvest diseases would require identifying microbes that effectively protect the harvested crop (Janisiewicz and Korsten, 2002).

Successful candidate identification starts with a suitable population of microbes to be evaluated. While screening processes are becoming more robust and generating higher throughput, less than 1% of candidate microbes make successful products (Bailey and Falk, 2011). The generation of large microbe collections, both through targeted and broad sampling techniques, is required for identifying biocontrol candidates. One example, Trichobank^TM, is a fungal culture collection of >2000 isolates of 21 Trichoderma spp. (Stewart et al., 2010). This collection has been successfully used to develop biocontrol agents like Sentinel^TM for the control of gray mold of grapes caused by Botrytis cinerea. In the case of microbe databases like Trichobank^TM, information on the isolates within the collection is matched to a desired set of biocontrol capabilities based on pathogen targets, host plants, mode of action, and environmental niche (Glare et al., 2012). This subset of selected isolates is then subjected to a series of standardized bioassays to establish biocontrol efficacy and field performance capability. It is worth noting here that biocontrol efficacy in a field setting is key for adoption and implementation of microbial products. While many biocontrol agents were identified and/or validated through in vitro screens, caution should be taken when assuming correlation between in vitro inhibition and field performance (Burr et al., 1996; Milus and Rothrock, 1997; Fravel, 2005). Screening strategies can follow varied approaches, but the desired outcome is the same in identifying efficacious, environmentally safe, and cost-effective biocontrol agents (Köhl et al., 2011; Ravensberg, 2011).

The most important factor for a successful product is the ability to increase or protect yield. This is obviously the most important goal and a given factor in combination with other factors mentioned below for overall product success. However, efficacy in the laboratory and/or greenhouse does not always translate to field success (Nicot et al., 2011). Whipps (2001) stated “The key to achieving successful, reproducible biological control is the gradual appreciation that knowledge of the ecological interactions taking place in soil and root environment is required to predict the conditions under which biocontrol can be achieved.” Nicot et al. (2011) suggests that the success gap between lab and field efficacy can be improved by understanding of in-field mode of action. Although they specifically refer to biocontrol microbes, this same principle applies to biofertility products as well. Efficacy data that do not account for ecological interactions in a complex microbe-plant field ecosystem including at least some of the factors discussed below risks failure (Fravel, 2005). In many cases biocontrol microbial products are included as a part of an integrated pest management program (Chandler et al., 2011).

In addition to in field-efficacy, there are often efficacy challenges that arise with scaling production for widespread distribution. Some of the challenges described by Takors (2012) include the genetic stability of the strain and the impact of mutation, viruses, and phase variation, as well as other chemical and physical factors associated with going from bench-top to industrial scale bioreactors.

Plants may recruit specific microbes based on their development and environment, responding to stresses or nutrient availability (Smalla et al., 2006; Hartmann et al., 2009). The effectiveness of microbial strains colonizing the plant are impacted by a number of biotic and abiotic factors (Barea, 2015), including the previous cropping history (Berg and Smalla, 2009; Peiffer et al., 2013), suggesting that microbial compositions of the soil are modulated by changes in cropping practices. The ability to colonize is also impacted by genotype of the plant, showing variations in community structure between variants in the same species (Siciliano and Germida, 1999; Briones et al., 2002). Specific plant exudates in the form of volatile organic compounds, carbon sources or organic acids encourage colonization and growth of a relatively narrow group of organisms (Sloan and Lebeis, 2015). For example, studies on Arabidopsis demonstrate not only bacteria-specific responses to targeted exudates like malic acid (Rudrappa et al., 2008), but also community responses over time due to development stage of the plant (Chaparro et al., 2014). In addition to targeted strains and temporal development of colonization, strains must also associate with the appropriate root architecture of the plant, whether by interaction with receptors on the surface of the roots or by maintenance of cell numbers within the rhizosphere influenced by the plant (Compant et al., 2010). These factors allow for selective colonization of specific microorganisms and promote diversity of the community to fit the functional needs of the plant (Mendes et al., 2015). Improving microbial support for a crop requires understanding the needs of the plant, in combination with the composition of the soil and the surrounding communities to best determine the products that will benefit the crop. However, it should be noted that there is often an ecological trade-off when selecting for a specific trait in a microbial strain. For example Ehinger et al. (2014) explored the relationship between Bradyrhizobium and either specialized or generalized hosts and found a trade-off in host range and efficacy. Conversely, selecting for or developing strains that are specialists and highly effective in desired traits such as biocontrol or host interaction can result in loss of fitness (Kassen, 2002).

Biocontrol microbial strains are often highly targeted to specific species of pests (Nicot et al., 2011), so farmers may need to apply different products to control multiple pest species. Relevant narrowed spectrum, short-lasting, slowing-kill microbial based products are big hurdles for successful product commercialization. For example, the fungus Colletotrichum gloeosporioides f. sp. malvae was discovered to cause seedling blight on round-leaved mallow plants being grown in weed control trials in Saskatchewan (Harding and Raizada, 2015). However, the diversity of weeds in the field combined with its narrow host range have limited its usage in the market. Since ecological interactions are so important to in-field efficacy, organisms that have greater versatility will have improved efficacy over a number of different field conditions. This versatility includes interaction with different hosts and different pathogens and will be an ongoing process as pathogens continuously evolve to circumvent plant defenses and overcome biocontrol mechanisms (Brockhurst and Koskella, 2013; Zhan et al., 2014).

Another important factor in the success of an inoculant or biocontrol product is practicality for both the producer and the consumer. The product must ideally have a low barrier to adoption and be compatible with the farmer’s equipment and production practices.

Mass production of the microbe responsible for improving crop yield is one of the prime requirements for commercialization (Moosavi and Zare, 2015). Pasteuria is a good case study of a product that in the past was not very practical from an industrial perspective due to difficulties with mass production. Pasteuria was originally described from water fleas over 100 years ago, however, cultivation efforts were unsuccessful (Metchnikoff, 1888). Nearly two decades later, Cobb (1906) discovered these organisms infecting a nematode. Pasteuria species are able to effectively parasitize different developmental stages of nematodes (Chen and Dickson, 1998), but for over a century commercialization of Pasteuria was limited due to the inability to mass produce spores as a product. Pasteuria penetrans is an obligate parasite of Meloidogyne species, which are obligate plant parasites (Davies, 2009). Until recently, harvesting spores for commercial product required extracting spores from infected nematodes extracted from infected plants and was not an ideal system for mass production. It is currently a commercial product Clarivar^® (Syngenta^®13).

Many farmers perceive inoculants and biocontrol microbial products as more costly and less effective than traditional agrochemicals. For example, microbial biocontrol strains are not always a quick acting option: they often work by suppressing pest populations through slower processes rather than killing on contact which may allow crop damage to continue for some amount of time. In some cases, to use biocontrol strains effectively, growers need to identify and know a great deal about the lifecycle of the pest or pathogen they are trying to control and understand the timing and appropriate conditions for application of the product. More outreach is needed between industrial or technical specialists and the agricultural community to help growers accustomed to broad-spectrum agrochemicals integrate inoculants and biocontrol microbial products into their cropping systems.

Appropriate formulation is required for a high quality product. Since microbial products are often stored under less than optimum conditions (e.g., high temperature, light exposure, high humidity), they must have an extended shelf life and the microorganism needs to be either robust or well protected to be able to survive under harsh conditions. Good formulation will also provide optimal conditions to enhance microorganism life on roots or on leaves to obtain optimal benefits after application to the target plants. To be widely adopted by farmers, an inoculant or biocontrol product must be cost effective and easy to apply, ensuring that the microorganisms are delivered to the target plant in the most appropriate manner and form. Formulation of inoculants and biocontrol products is a crucial issue but little research has been conducted on this subject. For some strains, particularly gram positive spore formers, formulation and long-term stability methods are much more developed than for gram negative strains. A literature survey by Xavier et al. (2004) showed that since the 1980s, most rhizobial research focused on the bacterial genetics and physiology and less than 1% of research articles on rhizobia have focused on formulation aspects of products. However, there is a real need for improved formulations of products, to create and commercialize new microbial products that will be more effective, stable, and higher quality to meet farmers’ needs.

Formulation of products by adding compounds to active ingredients can improve field performance, shelf life, and stability (Warrior et al., 2002; Leggett et al., 2011; Ravensberg, 2011), ultimately reducing variability. Formulation allows for several functional goals including safety, effective application, and enhanced persistence (Ravensberg, 2011). A lack of published research in this area is likely indicative of protection through intellectual property, like trade secrets, which is often necessary to protect investments in product development. Industry investments in current and future technologies will be critical in formulating novel products. One example of formulation utility is around microbes that do not form spores (e.g., gram negatives) or microbes that are highly sensitive to desiccation and temperature extremes. Serratia entomophila is the active ingredient in BioShield^®, an insect biocontrol agent (Glare et al., 2012). New formulation techniques have reportedly allowed for stabilization of BioShield^® to extend shelf life to more than 6 months without loss of viability (Swaminathan and Jackson, 2011). In addition, formulation additives like diluents and oils have been used successfully for Metarhizium acridium products, enhancing fungal spore attachment and infection in target insects (Hunter, 2010).

The microbial ecology of biocontrol agents has been shown to indicate whether they are rhizosphere or phyllosphere competent (Kamilova et al., 2005; Bruck, 2010; Vorholt, 2012). Formulation technologies can therefore be used to improve delivery, colonization, germination, and establishment of microbes in those particular zones. Seed coating with microbes can provide an inexpensive option for targeted delivery, but improvements still need to be made in coating materials, microbe and chemistry compatibility and application technology, especially when considering the diverse requirements of biological organisms (Glare et al., 2012). One of these requirements is water availability, which can have profound influence on survival of bio-products (Connick et al., 1996). Dry or desiccated products weigh less, are more cost effective to ship, and have a lower risk of contamination. This type of formulation may be amenable to microbes that produce stable storage structures like spores, but non-spore producers likely require different formulation strategies.

Closely tied to formulation parameters is the actual delivery system used to apply beneficial microbes in an agriculture setting. A delivery system targeting precise timing and specific sites can greatly improve both bioinoculant and biocontrol product efficacy, persistence, and cost-effectiveness. Delivery presents a major challenge to industry in part because it requires mass production, formulation, and application of biocontrol microbes and/or their bioactive compounds (Ravensberg, 2011; Glare et al., 2012). As previously mentioned, the biology of the microbe may dictate the best avenue for delivery, leading to decisions of application site (e.g., seed, foliar, root) and timing. Researchers are looking beyond traditional seed coats or foliar sprays and investigating aspects of timing and treatment location. Varied spray schedules of Trichoderma biocontrol strains were used to control gray mold and anthracnose in strawberries (Freeman et al., 2004). Continuous application of the Pseudomonas putida in low concentrations through irrigation water resulted in soil populations similar to a single application at a 10-fold higher concentration (Steddom and Menge, 2001). This suggests that targeted delivery systems (site and timing) can result in field efficacy in a cost-saving manner.

Some of the issues associated with failure of microbial products involve the timing of the application of the product in the field (Chutia et al., 2007). Microbial products tend to act on more specific targets and have a shorter shelf and sometimes active life than chemical fertilizer/pesticides (van Lenteren, 2012). The combination of selectivity of the microbial strain to host or target and lack of persistence often results in inconsistent field data (Nicot et al., 2011). For example, Bt toxin proteins are degraded very quickly when they are exposed to sunlight. Bt-based microbial products often need multiple applications and result in high cost. In other cases, the efficacy of a product presents a tradeoff between immediate short-lived impact and persistence in the environment (Barea, 2015). The persistence of strains varies greatly in the environment. Some strains such as Trichoderma harzianum and Bacillus amyloliquefaciens FZB42 decrease below detectable limits within a few weeks of application (Papavizas, 1982; Kröber et al., 2014), whereas other strains such as Rhizobium phaseoli and Bradyrhizobium japonicum will persist indefinitely, but at a lower abundance than is required for efficacy (Robert and Schmidt, 1983; Narożna et al., 2015). Some products may be formulated to successfully enable persistence of the product long enough to show activity due to compatibility between a strain and the environment if they can occupy a niche or colonize before competitors show up (Verbruggen et al., 2012) impacting community assembly in the rhizosphere (Nemergut et al., 2013). In cases where the biological product does not readily colonize the rhizo/phyllosphere, compatibility and niche space in the environment will severely impact efficacy.

High cost associated with production is another obstacle for success of developing a biological product. For example, AMF products generally contain spores, colonized roots, hyphae segments, or a mixture of the three (Dalpé and Monreal, 2004), and a wide range of carriers can be used (peat, compost, vermiculite, perlite, sand). Because AMF are obligate symbionts in nature, their proliferation and high-scale production require more specific skills and infrastructure. First attempts in AMF cultures used the pot-culture methods. Colonized root segments or spores of well-known AMF species are used to inoculate young seeds in a fresh sterile substrate. Plants are grown in pots, bags, or beds and the AMF colonize roots and substrate as the host develops, leading to a high concentration of AMF spores and colonized roots. Spores and roots obtained can then be used for commercial product preparation or to inoculate a new batch of sterile substrate. This kind of production method faced some difficulties such as uniformity of spores from batch to batch, production space requirements, and quality variation. In addition to production costs and return on investment for farmers, economic aspects of agricultural microbial products include market size and value (Nicot et al., 2011).

Regulatory frameworks and product registrations are used worldwide to guide the commercial development of microbial products. When developing new microbial products, the requisite regulatory framework varies by country, the product’s characteristics, and its intended usage. These national and international regulations must be taken into account during every part of the product development cycle, including its earliest stages, as certain regulations also outline where natural microbes can and cannot be harvested. Interestingly, the regulations pertaining to inoculants and biocontrol strains, while similar, may differ in certain parts of the world. Nevertheless, regulatory cycles for the development of new bioinoculants and biocontrol products are generally streamlined and well-articulated. As a result, microbial products are an appealing and cost-effective choice when taking an integrated, systems-level approach toward crop productivity and agricultural pest management.