Endophytic bacteria from Ziziphus jujuba enhance growth and salinity resilience in pearl millet under reduced fertilizer input

Salinity severely limits crop productivity in arid and semi-arid regions, necessitating the development of sustainable approaches for crop resilience against this abiotic stress. Conventional chemical fertilizers are used to enhance crop productivity, but their overuse harms soil health and profile. In this regard, endophytes from stress-adapted perennial plants represent a promising yet undiscovered strategy. Moreover, their potential to enhance crop performance in combination with sub-optimal doses of traditional chemical fertilizers remains largely unexplored. This study investigated the plant-growth-promoting (PGP) and stress alleviating potential of bacterial endophytes isolated from Ziziphus jujuba Mill. Bacillus safensis (Zj-Ea) and Pantoea septica (Zj-E2) in vitro exhibited superior multi-trait PGP capabilities and halotolerance respectively. These strains were tested in a greenhouse trial under four soil conditions [control, saline (150 mM NaCl), Diammonium phosphate (DAP: 12.5 mg/2.5 kg soil), DAP + NaCl amended] with four combination treatments (uninoculated, B. safensis , P. septica , and B.s + P.s) to promote the agronomic performance of pearl millet ( Pennisetum glaucum L.). Seed priming and soil drenching with these endophytes greatly enhanced germination metrics, vegetative growth, biomass accumulation and reproductive traits under both non-stress and stress conditions. Under control conditions, a consortium of both strains produced the strongest overall growth responses, while individual strains optimized specific germination profiles. Under saline conditions, co-inoculation significantly outperformed individual strains. Endophytic-DAP synergy yielded the greatest stress alleviation; markedly increased photosynthetic pigments, osmolyte accumulation and antioxidant enzyme activities, while reducing oxidative stress markers. The results indicate that Z. jujuba- derived endophytes alleviate salinity stress in pearl millet through improved osmoregulation and redox homeostasis. Concurrently, these strains acted as biofertilizers under control conditions, enhancing pearl millet productivity via the synthesis of IAA and siderophores, ammonia production, and by phosphate solubilization. Our findings also demonstrated that a strategically engineered consortium (highly halotolerant strain with robust plant-growth-promoting strain) produces more prominent results, particularly under salt stress. The efficacy of dual-strain consortium in combination with reduced doses of DAP fertilizer highlights their potential as sustainable biofertilizer strategy for optimizing crop productivity in salinity-stressed agriculture, pending validation under field conditions.