Influence of Agronomic Practices on the Antioxidant Activity of Three Mediterranean Officinal Wild Plants: Silybum marianum, Achillea millefolium, and Trifolium pratense

The aim of this study was to evaluate the influence of various agronomic factors on plant growth and the accumulation of secondary metabolites with antioxidant properties. The three Mediterranean Officinal Wild Plants selected for this investigation were Silybum marianum, Achillea millefolium, and Trifolium pratense whose extracts, enriched in phenolic compounds, are well documented for their potential therapeutic effects. Three agronomic factors were evaluated, each with two treatment options, resulting in eight experimental combinations: (1) inoculation with plant growth-promoting rhizobacteria (PGPR) versus control (no inoculation); (2) high versus low fertilization rates of K₂O and P₂O₅ to modulate nutrient availability; (3) water stress at 40% of field capacity compared to the control with full field capacity. Plant growth was monitored using the BBCH (Biologische Bundesanstalt, Bundessortenamt and CHemical industry) scale to delineate key phenological phases, with treatments applied until the flowering stage was reached. Only the leaves of the plants were collected, and hydroalcoholic extracts were prepared for the evaluation of total antioxidant capacity (TAC) using the FRAP, DPPH, and ABTS assays. These assays were selected due to their complementary insights into the chemical mechanisms underlying TAC, as well as their ability to assess the physicochemical characteristics of the phytochemical constituents.