Combined Effects of Arbuscular Mycorrhizal Fungi, Plant Growth-Promoting Rhizobacteria, and Mineral Fertilization on the Physiological, Biochemical, and Nutritional Properties of Chilaca Chili Pepper (Capsicum annum L.)

Pepper fruits contain diverse primary and secondary metabolites, including ascorbic acid, carotenoids, phenolics, and flavonoids, which contribute to nutritional quality, antioxidant capacity, coloration, and consumer acceptance. Chilaca chili pepper (Capsicum annuum L.) is a Mexican cultivar valued for its distinctive flavor and pungency, representing a valuable resource for studying fruit quality and sustainable crop improvement. This study evaluated the individual and combined effects of arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) on growth, physiological responses, antioxidant activity, and fruit quality traits. Twelve treatments in a 3 × 2 × 2 factorial designs were evaluated for chlorophyll, soluble solids, biomass, APX and LOX activities, and vitamin C and capsaicin contents at three ripening stages (green, mid-red, and red). Enzyme activities were determined spectrophotometrically, and bioactive compounds were quantified from methanolic fruit extracts. Microbial inoculation primarily improved fruit physiological quality rather than vegetative growth. Biomass and growth traits showed no significant differences among treatments (p > 0.05), whereas biochemical responses exhibited distinct ripening-dependent patterns. APX activity, vitamin C, and capsaicin increased from green to mid-red stages and declined at full ripeness. Bacillus sp.-based treatments (T1 and T2) produced a significant transient increase in LOX activity during mid-ripening, while T7 showed a similar but weaker response. AMF progressively enhanced LOX activity and capsaicin accumulation in green fruits. PGPR effects were strain-dependent, with Bacillus sp. promoting early capsaicin accumulation and A. deleyi favoring higher levels during advanced ripening. Overall, AMF and PGPR differentially regulate antioxidant metabolism, vitamin C accumulation, and capsaicinoid biosynthesis while interacting with mineral fertilization to improve fruit quality. These findings support beneficial microorganisms as sustainable tools for enhancing nutrient-use efficiency and fruit nutritional and functional value without replacing mineral fertilization.