Sunscald and ultraviolet light injury of banana fruits

Abstract

The peel of green banana fruit affected by sunscald or irradiated with ultraviolet (UV)-C (but not UV-A) was superficially bronzed by the deposition of a red-brown pigment in epidermal and adjacent hypodermal cells. Bronzing increased with the UV-C fluence, with maximum response at 720 Jm'2. Pigment deposition was first detected about 24 h after irradiation, and continued for about a week. Bronzing was greatest in fruit kept in darkness after irradiation, and was lessened by exposure to white light. Continuous exposure to white light (13.2 Wm'2) completely prevented bronzing. Green fruit in which bronzing had been prevented with white light after irradiation with UV-C became bronzed when irradiated a second time and incubated in the dark. As banana fruit ripened they became less sensitive to UV-C, and after seven days of ripening at 20°C, irradiation with UV-C caused no visible effects.