Symbiotic fungi as biotechnological tools: Methodological challenges and relative benefits in agriculture and forestry

Environmental conditions are becoming increasingly challenging in managed ecosystems, especially in agricultural fields, where environmentally friendly solutions are urgently needed. Fungal symbionts offer great opportunities to enhance crop production and ecosystem sustainability under environmental stress. Some fungi are relatively well investigated (e.g., arbuscular mycorrhiza) and regularly used in commercial products, while others, such as fungal endophytes, are not well-known in this market, yet. Here, we review I) the characteristics and benefits, II) the advantages and challenges of principal isolation, preservation, inoculation, and field applications methods, and III) the environmental stress resistance mechanisms for different beneficial fungi. Utilization of mycorrhizae is still facing many challenges, particularly in terms of acquiring pure cultures and successfully establishing their symbiosis in the field. Effects of mycorrhizal associations on the above-ground organs through molecular mechanisms are not fully understood. Although biochemical values of some endophytes are well recognized, molecular mechanisms involved in endophytic-induced stress tolerance are poorly known. Fungal endophytes present several important advantages over mycorrhizal fungi including broader host range as well as straightforward isolation and application protocols. Further studies are necessary for selecting the best strains and communities, producing inoculum on a large-scale, and understanding the potential environmental hazards.