Nano-encapsulated biostimulant enhances growth and postharvest quality of chili peppers (Capsicum annuum)

• Microbial and botanical bio-stimulants improve the quality of chilli fruits. • Nano-encapsulated biostimulants positively influence the phytochemical content in chilli fruits. • Nano-encapsulated biostimulant application to soilless medium is proven effective. • Co-application of microbial and botanical bio-stimulants positively affects plant growth, yield, and quality. Biostimulants play a vital role in improving the postharvest quality of agricultural produce. However, biostimulant efficiency assessment is mainly based on vegetative growth and crop yield. The function of biostimulants must be evaluated thoroughly to determine their contribution to enhancing the phenotypic characteristics and nutritional value of produce. This study evaluated a new formulation of microbial and botanical biostimulants on the capsaicin, ascorbic acid, flavonoid, and phenolic content of chilies. Biostimulant treatment recorded 0.618 quantum yield (QY) value compared with 0.581 quantum yield value of plants not treated with biostimulants, representing the plant's photosynthetic capacity. The chili plants treated with the biostimulant showed a significant increase in height and yield, which accounted for 60 cm of mean value and 575.41 g than plants that were not treated with the biostimulants, which represented 53 cm height of the mean value and 522.16 g of yield. Chili plants treated with biostimulant showed a higher L value, −15.38 ± 11.9 and a chroma value of 8.77 ± 5.56 in chili fruits compared to −8.29 ± 7.97 of l-value and 5.30 ± 6.81 mean chroma value in chili plants not treated with biostimulants. Red chilies harvested from plants that were not treated with biostimulants recorded the highest phenolic content (1.332 ± 0.56 mg/L) compared to the chilies that were treated with biostimulants (0.8830 ± 0.19 mg/L). In contrast, red chilies harvested from the plants treated with biostimulants recorded the highest flavonoid content (15.77 ± 1.0 mg/L) than plants not treated with biostimulants (13.098 ± 1.8 mg/L). Biostimulant treatment enhanced the capsaicin content in the early stages of chili development. The highest ascorbic acid content in chilies treated with biostimulants (144.29 ± 6.1 mg/L), followed by green chilies treated with biostimulants twenty-seven days after anthesis (132.85 ± 1.67). These results indicate the potential of nano-encapsulated microbial and botanical biostimulants to improve the postharvest quality of chili fruits.