Integrating Chitosan and Probiotic Biostimulants for Nutritional and Functional Fortification of Onion ( Allium cepa L.)

Onions, rich in bioactive and mineral compounds, face quality challenges from climate variability and poor agronomic practices. Meanwhile, biostimulants like chitosan and probiotic microbes have demonstrated to improve crop quality under unfavorable conditions. Accordingly, this study evaluated the effects of chitosan (100 and 200 ppm), Paraburkholderia (1.5 × 10 9 CFU mL −1 ), and clybio (yeast and Bacillus blend, 0.5%) applied individually or in combinations across eleven treatments besides control. Foliar sprays were administered at 20, 40, and 60 days after transplanting. Notably, chitosan 100 ppm + Paraburkholderia + clybio performed the best through improving biochemical and functional profiles by 25%–85% over control, particularly dry matter, total sugars, total phenolic, and total flavonoid contents by 23%, 40%, 37%, and 87%, respectively. Chitosan 200 ppm + Paraburkholderia + clybio exhibited statistical similarity in most cases. These formulations also significantly boosted mineral constituents (K, Na, Mg, Ca, Fe, S, P) by 4%–65% over untreated. Interestingly, chitosan‐based treatments consistently outperformed those without it. Moreover, strong positive correlations and clustering of these treatments in favorable quadrant with key quality traits indicate synergistic improvement of onion quality by biostimulant application. Thus, chitosan and plant probiotics integration can be recommended for enhancing onion quality in challenging environments.