Preharvest Bunch Spraying of Chitosan Reduces Biotic Stress, Enhances Antioxidant Activity, and Extends the Shelf Life of Bananas

Chitosan (CHT) is a biopolymer-based elicitor and is widely recognized for activating plant defense systems and postharvest preservation. However, its potential role in preharvest application in banana is poorly understood. Herein, an experiment was conducted in 2023−2024 and 2024−2025 under subtropical field conditions in Dinajpur, Bangladesh, to investigate the effects of CHT treatments on the incidence of pests, diseases, and fruit quality of banana. CHT was applied four times just after the opening of the flowers in the bunches at 25-day intervals using four concentrations of 0, 5, 7.5, 10, and 12.5 mg L −1 in a completely randomized design (CRD) with three replications. Results revealed that CHT slightly enhanced fruit weight and firmness by 1.84−1.90% and 17.67−43.18%, respectively, compared with the control in both experimental years. Biotic stress parameters were markedly reduced, with insect infestation, disease infection, and physiological disorders decreasing by 80%, 87%, and 85% in the 1st year and 83%, 87%, and 85% in the 2nd year, respectively. CHT improved total soluble solids and β-carotene content while reducing titratable acidity. Additionally, the total phenol, flavonoid, and antioxidant activities were significantly increased by 41–48%, 28−31%, and 21–25%, respectively, compared to the control due to the application of 10 mg L −1 CHT, accompanied by reduced peel yellowing ( b * value) and slower ripening progression during storage. Importantly, 10 mg L −1 CHT extended the shelf life up to 9 days in both experimental years. These findings exhibited that preharvest CHT treatment effectively enhanced banana fruit quality, reduced biotic stress, and extended postharvest life, providing a sustainable strategy to minimize postharvest losses and support safe fruit production.