The reduction of crown rot disease observed in UVC-irradiated banana fruit, 'Berangan' was associated with activation of the defense response mechanisms, increased peroxidase and polyphenol oxidase activities as well as accumulation of lignin and phenolic compounds in its crown tissue, but not phenylalanine ammonia-lyase activity. Transmission electron microscope micrographs revealed that 0.01 kJ m⁻² UVC retarded the losses of cell compartments and disintegrations of fibril fraction in cell wall structure of the crown tissue. UVC treatment 24 h after fungal inoculation induced the accumulation of phenol-storing cells that could create an antimicrobial environment in the host tissue for combating the fungal colonization. Moreover, formation of cell wall lignification and heterogenous matrix of cell wall appositions at site of fungal penetration was clearly observed in UVC-irradiated crown tissue, which otherwise absent in the control crowns. These structures might be important physical barriers that were induced by the irradiation to prevent diffusions of toxin and enzyme from the crown rot-infecting fungi.

Crown rot caused by fungal pathogen is the most prevalent postharvest disease in banana fruit that results significant economic losses during transportation, storage, and ripening period. Antifungal effects of ultraviolet C (UVC) irradiation at doses varied from 0.01 to 0.30 kJ m−2 were investigated in controlling postharvest crown rot disease, maintenance of fruit quality, and the effects on antioxidant capacity of Berangan banana fruit during ripening days at 25 ± 2°C and 85% RH. Fruits irradiated with 0.30 kJ m−2 exhibited the highest (i.e., 62.51%) reduction in disease severity. However, the application of UVC at all doses caused significant browning damages on fruit peel except the dose of 0.01 kJ m−2. This dose synergistically reduced 46.25% development of postharvest crown and did not give adverse effects on respiration rate, ethylene production, weight loss, firmness, color changes, soluble solids concentration, titratable acidity, and pH in banana as compared to the other treatments and control. Meanwhile, the dose also enhanced a significant higher level of total phenolic content, FRAP, and DPPH values than in control fruits indicating the beneficial impact of UVC in fruit nutritional quality. The results of scanning electron micrographs confirmed that UVC irradiation retarded the losses of wall compartments, thereby maintained the cell wall integrity in the crown tissue of banana fruit. The results suggest that using 0.01 kJ m−2 UVC irradiation dose as postharvest physical treatment, the crown rot disease has potential to be controlled effectively together with maintaining quality and antioxidant of banana fruit.