Even individual microbial strains can employ different modes of action to protect plants from diseases [147,148]. However, it has been proposed that using a mixture of bacteria can enhance the biocontrol effect in terms of not only its stability and the spectrum of application (in terms of the plant, soil type, and pathogen) but also its magnitude [149,150]. In nature, bacteria exist in complex, multispecies consortia with numerous interspecies and interkingdom interactions [63]. Therefore, employing multiple microorganisms as a consortium is expected to benefit their performance due to these interactions [5]. Therefore, this is why microbial consortia are commonly used as biofertilizers [151]. However, there are relatively few biocontrol products containing microbial consortia [34], not only due to the more problematic registration [152] of multiple-component-containing products but also to difficulties in the prediction of interactions between their components [153]. Microorganisms used for biocontrol usually produce a wide array of antimicrobial compounds, and the same modes of action used to fight the pathogens can negatively affect other consortium components [103]. For example, Pseudomonas fluorescens A506 degrades the antibiotics produced by strains Pantoea vagans C9-1 and Pantoea agglomerans Eh252, reducing their activity against the fire blight of pear [154]. This indicates incompatibility between the tested strains, highlighting the importance of confirming compatibility when composing consortia for biological plant protection. The same mechanisms used by biological control agents against plant pathogens (such as parasitism, predation, antibiosis, competition, and production of lytic enzymes but also digestion of substances responsible for their activity) can reduce the activity of other BCAs. On the other hand, BCAs can increase the protective effect with the use of alternative modes of action, different environmental preferences or by the induction of the secondary metabolism of other consortium components (Figure 2). There are various methods for assessing strain compatibility, each with its own advantages and disadvantages. However, the most commonly used approach to evaluate the biocompatibility of strains and their activity against selected pathogens relies on direct antagonism on artificial media [34]. Since microbial secondary metabolisms are highly dependent on the nutrients available [155], it has been suggested that strains for biological plant protection should be selected based on their in vivo rather than in vitro activity [156]. We believe that this principle should be applied to the selection and composition of microbial consortia, as the interactions within the consortium have a significant impact on its overall performance [5].

Table 1 provides an overview of the biocontrol products available on the market. Although knowledge transfer from science to industry may not occur rapidly, and various factors impact the selection of products on the shelves, it offers valuable insights into the potential for success. In the literature, numerous examples of complex consortia involving different microorganisms for combating various diseases can be found [5]. However, this diversity is not fully reflected in the range of biocontrol products registered for crop protection (Table 1). Farmers have access to multiple approved biological control products based on only a limited number of different microbial consortia. The challenges in registering products with multiple active ingredients contribute to this situation. Additionally, it is noteworthy that the current solutions for biocontrol predominantly rely on the use of Trichoderma spp. [157], despite the wide array of microorganisms available for such purposes.

Trichoderma is an extensively studied genus for biological plant protection, and numerous studies focus on identifying new isolates with promising biocontrol potential [158,159]. The popularity of this genus stems from the number of modes of action utilized by Trichoderma spp. [160] and the resulting potential to not only protect plants from important pathogens [161] but also to produce spores with a high survival rate during formulation [162]. Additionally, their ability to promote plant growth enables the use of Trichoderma strains as both biocontrol agents and biofertilizers [163]. We anticipate that this newly discovered Trichoderma species will quickly find their way onto the market of biocontrol products [164].

On the other hand, there are a wider range of species utilized in consortia for biofertilizers or biostimulants [165,166]. However, the legal status of these consortia, similar to biocontrol products, is in urgent need of revision [24,25,26,167]. Nevertheless, the relatively low number of biocontrol formulations can also be attributed to inadequate knowledge exchange between industry and academia [168,169]. Therefore, it is imperative to improve communication among scientists, plant protection product producers, farmers, and regulatory authorities. By enhancing collaboration, we can meet technological demands, address pressing agricultural challenges, and establish a safe and efficient environment for the registration of biocontrol products.