Salicylic acid modulates yield and bioactive compound accumulation in chili pepper depending on fruit ripening stage

Salicylic acid (SA) is an endogenous signaling molecule involved in the regulation of plant growth, development, stress responses, and secondary metabolism. Although the effects of exogenous SA and fruit ripening on pepper growth and biochemical composition have been investigated separately, the extent to which SA application modulates yield and bioactive compound accumulation across distinct fruit maturity stages remains insufficiently characterized. This study investigated the effects of foliar SA application on yield, physical fruit quality, biochemical properties, and antioxidant capacity at three maturity stages of chili pepper. A field experiment evaluated three SA treatments (0, 1, and 2 mM) across three maturity stages (green, brown, and red). Fruit maturity significantly affected most evaluated traits, whereas SA application significantly affected yield and selected biochemical and antioxidant traits; significant maturity × SA interactions occurred for several biochemical and antioxidant traits and fruit L*. The 1 mM SA treatment yielded the highest fruit production (1239.86 g m⁻²), and the brown stage had the highest observed mean fruit weight (19.95 g). Mean fruit weight under 1 mM SA was 19.51 g versus 18.60 g in the control, corresponding to a 4.89% increase relative to the control. The red stage had the highest observed mean values for dry matter, Vitamin C, TPC, TFC, DPPH, and FRAP. Overall, 1 mM SA had the highest mean Vitamin C (236.89 mg 100 g⁻¹), TPC (300.92 mg GAE 100 g⁻¹), DPPH (10.06 µmol TE g⁻¹), and FRAP (6.10 µmol TE g⁻¹) among SA treatments. The highest TPC (406.62 mg GAE 100 g⁻¹) was recorded in red-stage fruits from plants treated with 1 mM SA. Fruit maturity was the predominant factor associated with variation in bioactive compound accumulation and antioxidant capacity, while SA modulated these responses in a dose- and maturity-dependent manner. The 1 mM SA treatment showed the most consistent responses for fruit yield and selected biochemical and antioxidant traits, although effects were not uniform across all parameters. These findings highlight the importance of fruit developmental stage when evaluating the physiological and biochemical effects of exogenous SA in chili pepper.