Combining Indigenous Endophytes with Reduced NPK Fertilization Enhances Yield and Phytochemical Quality of Roselle ( Hibiscus sabdariffa L.) in Arid Conditions

The intensive use of chemical fertilizers in medicinal plant production raises significant environmental and quality concerns, particularly under arid and high-temperature conditions. This study investigated the effectiveness of indigenous endophytic bacteria consortium as a sustainable approach to reduce mineral fertilizer inputs while improving the growth, yield, and phytochemical quality of roselle ( Hibiscus sabdariffa L.) under Upper Egypt conditions. A field experiment was conducted during the summer of 2024 in Aswan, Egypt, using a factorial randomized complete block design. Treatments included a ten-strain endophytic consortium applied alone or combined with 25%, 50%, and 75% of the recommended NPK dose, alongside an unfertilized control and 100% NPK alone. Results highlighted clear percentage-based improvements with integrated treatments. The combination of 75% NPK with endophytic inoculation increased dry calyx yield by 16% relative to the conventional 100% NPK treatment. Significant increases were also observed in vegetative growth, fruit number, biomass accumulation, and photosynthetic pigments relative to full chemical fertilization. Moreover, antioxidant activity and concentrations of anthocyanins, phenolics, and flavonoids were maintained or enhanced under reduced fertilizer regimes, indicating qualitative gains without yield penalties. In contrast, complete fertilizer omission caused marked reduction in growth and yield parameters. Overall, substituting 25% of mineral fertilizers with indigenous endophytic inoculation not only sustained productivity but generated measurable yield gains, improved nutrient use efficiency, and strengthened crop resilience, demonstrating a practical and environmentally sound strategy for sustainable roselle cultivation in arid regions.