1 © Springer Nature Switzerland AG 2020 A. N. Yadav et al. (eds.), Agriculturally Important Fungi for Sustainable Agriculture, Fungal Biology, https://doi.org/10.1007/978-3-030-45971-0_1 Chapter 1 Agriculturally Important Fungi: Plant–Microbe Association for Mutual Benefts Fatma Ahmed Abo Nouh, Hebatallah H. Abo Nahas, and Ahmed M. Abdel-Azeem Contents 1.1 Introduction 1 1.2 Plant-Symbiotic Nitrogen Fixation Association 3 1.2.1 Nitrogen Fixing in Legumes 4 1.2.2 Nitrogen Fixing in Actinorhizal Plants 5 1.3 Plant–Mycorrhizas Association 5 1.3.1 Examples of Specifc Activities of AMF 6 1.4 Plant–Endophyte Association 7 1.4.1 Fungal Endophyte 7 1.4.2 Bacterial Endophyte 8 1.4.3 Examples of Specifc Activities of Endophytes 9 1.5 Conclusion and Future Prospects 12 References 12 1.1 Introduction Plants represent a very dynamic system, refecting a great capacity for adaptation in constantly fuctuating surroundings. This ability is particularly advantageous in the areas that are prone to intensive agriculture or biotic or abiotic vagaries (Bhandari and Garg 2017). Plants are exposed to huge numbers of microorganisms that are present in the top soil and are found on leaves and stems (Sivakumar and F. A. A. Nouh · A. M. Abdel-Azeem (*) Systematic Mycology Laboratory, Botany Department, Faculty of Science, University of Suez Canal, Ismailia, Egypt H. H. Abo Nahas Zoology Department, Faculty of Science, Suez Canal University, Ismailia, Egypt