Development of agricultural bio-inoculants based on mycorrhizal fungi and endophytic filamentous fungi: co-inoculants for improve plant-physiological responses in sustainable agriculture

A new more sustainable agricultural system needs to be developed to increase production without compromising human and animal health and preserving essential resources, such as soil, water and diversity. Bio-inoculants can be a tool to favor this transition, as they can replace or complement agrochemicals that do not meet the above premises. Bio-inoculants generated from endophytic filamentous fungi and mycorrhizal fungi, whether used individually, in combination with each other or with other microorganisms, stand out for their potential. This review provides information on how bio-inoculants based on these microorganisms have been shown to increase crop yield and quality through strategies, such as increasing nutrient uptake or levels of certain phytohormones. On how they can promote tolerance to abiotic stresses, including heavy metals, elevated temperatures, salinity or drought, through strategies, such as the accumulation of osmoregulatory substances or increasing the plant's root surface, among others. And finally, in the ability to protect the plant against pathogens and pests, either by inducing defense systems, competing for space or synthesizing metabolites with antibiotic activity. It should be noted that, although there are already commercial products using these microorganisms for agricultural purposes, such as biological control agents or biostimulants, it is expected that a deeper understanding of the mechanisms of action of the microorganisms, together with improved technical production processes, will lead to more effective, safer and cheaper products.