Foliar Application of a Methanolic Extract of Ricinus communis L. Modulates Growth, Yield, Photosynthetic Pigments, and Antioxidant Capacity of Jalapeño Pepper (Capsicum annuum L.) Under Open Field Conditions

The jalapeño pepper (Capsicum annuum L.) is a crop of great economic and nutritional importance worldwide; however, increasing yield and quality under conditions of reduced synthetic inputs remains a significant challenge, mainly due to restrictions in plant nutrition and stress response capacity; in this context, plant-based biostimulants, such as Ricinus communis extracts, are of particular interest due to their potential to modulate plant metabolism, promote growth, and favor the accumulation of bioactive compounds. In this study, the effect of a foliar-applied biostimulant derived from a methanolic extract of Ricinus communis L. on the physiological, agronomic, and biochemical parameters of jalapeño peppers was evaluated under open field conditions. A randomized complete design with five treatments was established: three extract concentrations (T50: 50 mg L−1, T75: 75 mg L−1, and T100: 100 mg L−1), a commercial biostimulant (Pepton 85/16 ®), and an absolute control. Significant differences (α ≤ 0.05) were observed between treatments T50, T75, and T100 with the application of castor bean and the absolute control in stem diameter, fruit number, yield, and polar and equatorial fruit diameter, as well as phenols, flavonoids, and antioxidant capacity (ABTS and DPPH). The application of R. communis extract (T50, T75, and T100) significantly improved plant performance compared to the control, particularly in yield (up to 270%), fruit number (73%), shoot biomass (up to 38%), and root development (up to 32%). Furthermore, increases in chlorophyll content and in antioxidant-related compounds were observed, including phenols, flavonoids, ABTS, and DPPH (up to 17%). Spearman correlation analysis revealed strong associations between structural and metabolic variables, highlighting the relationship between stem diameter, fruit traits, and bioactive compound accumulation, as well as the link between chlorophyll content and reproductive performance. The 1H NMR analysis indicated the presence of secondary metabolites such as ricin, unsaturated fatty acids, and phenolic compounds; however, their isolation and relationship with the biostimulant activity of the extract require further specific studies. Overall, foliar application of R. communis extract improved the growth, productivity, and biochemical attributes of jalapeño pepper, highlighting its potential as a sustainable alternative for crop management.