Rationally designed Bacillus-Pseudomonas consortium with synergistic control of potato late blight through biochemical defenses and physiological optimization

The oomycete Phytophthora infestans , causal agent of potato late blight, remains a major constraint to global potato production due to its rapid evolution and resistance to fungicides and host resistance genes. While single-strain biocontrol agents offer sustainable alternatives, their inconsistent field performance limits widespread adoption. Here, we demonstrate that a rationally designed consortium comprising Bacillus amyloliquefaciens BaC21 and Pseudomonas fluorescens DS17R provides synergistic protection against late blight through multilayered mechanisms. From 22 rhizosphere Bacillus isolates, BaC21 was selected for its superior antagonism (18.80 mm inhibition zone, 91.66% volatile-mediated suppression, 76.8% cell-free filtrate activity). Co-inoculation enhanced root colonization of both strains, with Bacillus populations increasing 1.19-fold and Pseudomonas 1.11-fold over single applications. Under greenhouse conditions, the BDR consortium reduced disease severity by 80.8%, significantly outperforming single strains. Field trials confirmed efficacy comparable to the fungicide Ridomil, with BDR-treated plots yielding 24.8 t.ha ^− 1 a three-fold increase over untreated controls. Mechanistically, the consortium induced temporally coordinated phytohormone signaling: early jasmonate/ethylene peaks (JA: 95 ng.g ^− 1 FW at 12 h; ethylene: 6.0 nL.g ^− 1 FW/h at 12 h) followed by sustained salicylate accumulation (550 ng.g ^− 1 FW at 48 h, r = -0.92 with AUDPC), circumventing SA-JA antagonism. This primed state activated phenylpropanoid metabolism (PAL 2.98 µmol h ^− 1 mg ^− 1 protein), lignin deposition (38.5 mg.g ^− 1 DW), and antioxidant capacity (cysteine 265 nmol.g ⁻¹ FW) without compromising photosynthesis (chlorophyll maintained at 2.35 mg.g ^− 1 FW). Synergy factors reached 1.50 for disease reduction and 1.62 for yield increase. This work establishes a mechanistic framework for rationally designing microbial consortia that integrate ecological, hormonal, and biochemical complementarity for sustainable crop protection.