Azospirillum spp. as bio-innovative defenders: Metabolomic signatures and molecular defense reprogramming in plant immunity against fungal phytopathogens.

Fungal diseases accounts for nearly 30-40% of global crop yield losses, underscoring the need for sustainable alternatives to chemical fungicides. Azospirillum spp., traditionally recognized for plant growth promotion, have emerged as potent biocontrol agent with multifaceted defense functions. Beyond niche competition and siderophore production, Azospirillum primes host immunity through reprogramming primary and secondary metabolism and activating systemic defense pathways such as salicylic acid (SA), jasmonic acid (JA), and induced systemic resistance (ISR). Metabolomic analyses reveal its influence on amino acids, sugars, phenolics, flavonoids, terpenoids, and phytohormones, while enhancing antioxidant systems. Integration of metabolomic and transcriptomic data identifies key regulatory genes and metabolites linked to fungal suppression. This review comprehensively summarizes molecular defense mechanisms, highlighting omics-based, and proposes metabolomics-guided applications of Azospirillum for sustainable and resilient crop protection.