Effects of an endophytic bacterial consortium derived from Zingiberaceae on growth, yield, and curcuminoid biosynthesis in Curcuma longa L.

Endophytic bacteria, integral to the plant microbiome, possess considerable potential for improving the cultivation and sustainability of medicinal plants. These bacteria are essential for various plant functions, including growth enhancement, nutrient uptake, and resistance to biotic and abiotic stressors. This study recovered 29 endophytic bacterial isolates from the rhizomes of five Zingiberaceae species: Zingiber officinale, Curcuma longa, Kaempferia galanga, Alpinia purpurata, and Hedychium coronarium. These isolates were evaluated for plant growth-promoting (PGP) traits, including mineral solubilization, indole-3-acetic acid (IAA) production, siderophore production, ammonia production, and hydrogen cyanide (HCN) production. From these, superior isolates were chosen to create five distinct compatible consortia, whose plant growth-promoting (PGP) activities were further assessed to ultimately identify the most effective consortium, C4, which included Bacillus sp. and Lysinibacillus sp., and exhibited the highest overall PGP activity among the consortia tested. In vivo assessment utilizing mung bean determined 10⁸ CFU mL⁻¹ as the optimal inoculum concentration, demonstrating the greatest improvement in vegetative development. The subsequent field application in turmeric markedly enhanced plant height (36.5%), leaf area (28.8%), tiller production (82.1%), and rhizome yield (69.6%) relative to the control. The re-isolation of the inoculated bacteria from harvested rhizomes supported their persistence within plant tissues under field conditions. Consortium-treated plants exhibited enhanced biochemical quality, evidenced by estimated increases in curcumin (29.7%), demethoxycurcumin (26.0%), bisdemethoxycurcumin (40.7%), total curcuminoids (30.2%), and volatile oil content (5.4%). Quantitative real-time PCR demonstrated a 1.51-fold upregulation of the curcumin synthase gene (CURS2), which was associated with increased curcuminoid accumulation, suggesting a potential influence on curcuminoid biosynthesis. These findings demonstrate that consortium C4 represents a promising eco-friendly microbial bioinoculant for sustainable turmeric cultivation and quality improvement.