Evaluation of the nutraceutical and antimicrobial properties of tagetes patula cultivar "Strawberry Blonde" plants grown under different water and fertilization regimes

Abstract

Tagetes patula, commonly known as French marigold and recognized for its ornamental use, has widely documented nutraceutical and antimicrobial properties. In this study, the influence of different irrigation and fertilization regimes (organic and inorganic) on floral development, bioactive compound production, and bacterial growth inhibition of the ‘Strawberry Blonde’ cultivar of this species was evaluated, in plants grown in a soil-free system. The experiment was conducted in a greenhouse using a 2 × 2 factorial design: normal irrigation (RN) and restricted irrigation (RR), combined with organic fertilization (FO) and inorganic fertilization (FI), resulting in four treatments: RNO (normal irrigation, organic fertilization), RRO (restricted irrigation, organic fertilization), RNI (normal irrigation, inorganic fertilization), and RRI (restricted irrigation, inorganic fertilization). Floral yield parameters, normalized difference vegetation index (NDVI), colorimetry (CIELab model) and bioactive compound content (phenols, flavonoids, carotenoids) were evaluated using spectrophotometric and HPLC methods. Antioxidant capacity (DPPH) and antimicrobial activity against Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa were also determined. RNO presented the best agronomic results, with higher floral fresh weight (2.37 g/head), number of flowers per plant (4.94) and NDVI (0.69). Treatments with restricted irrigation, on the other hand, showed higher total phenol content and antioxidant capacity at advanced stages of the crop. RNI stood out for its higher flavonoid content (16.74%) and antioxidant capacity (52.8%). HPLC analysis allowed the identification of compounds such as quercetin (up to 490.5 µg/g), kaempferol and several phenolic acids. Ethanol 70% was the most efficient solvent for quercetin and kaempferol extraction. The ethanolic and methanolic extracts exhibited significant antimicrobial activity against S. aureus (halos up to 16.8 mm) and moderate antimicrobial activity against E. coli, while presenting no inhibition against P. aeruginosa. In conclusion, the type of fertilization, harvest time, and extraction solvent influenced the content and efficacy of secondary metabolites. The RNO combination optimized flower fresh weight yield and visual quality, while restricted irrigation induced the synthesis of bioactive compounds without compromising dry weight. T. patula showed promising potential as a source of nutraceutical and antimicrobial compounds, with ethanol 70% standing out as an effective solvent for their extraction.