Interaction of Azospirillum spp. with Other Bacteria and Fungi

Abstract

Azospirillum has attracted considerable attention as a microbial inoculant due to its diverse plant-beneficial effects, such as nitrogen-fixing, enhanced nutrient availability, production of phytohormones such as indole-3-acetic acid (IAA), cytokinins, and gibberellins, and improvement of plant tolerance to abiotic and biotic stresses. Furthermore, their co-inoculation with other plant-beneficial microorganisms can lead to more consistent and significant yield improvements, and it has emerged as a promising strategy for sustaining plant growth. This review chapter first explores the in vitro interactions between Azospirillum and other microbial partners, highlighting antagonism interaction on Azospirillum or of Azospirillum on other rhizosphere microbial members, synergistic interactions, and even exploitation by Azospirillum of public goods produced by other beneficial rhizobacteria. It then discusses how these interactions can be exploited in planta to improve Azospirillum root colonization, enhance its antifungal activity, or improve symbiotic relationships through co-inoculation with mycorrhizal fungi or nitrogen-fixing bacteria such as Bradyrhizobium. Finally, optimized protocols are proposed for evaluating the in vitro compatibility of Azospirillum strains with other microorganisms and assessing the efficiency of co-inoculation on plant performance. Altogether, the data presented in this review underscore the value of integrating Azospirillum with complementary plant growth-promoting rhizobacteria (PGPR) partners to sustainably enhance crop productivity.