How to recognize the damage caused by excessive sun exposure to fruit

Sunburn, or excessive sun exposure, is a physiological disorder of fruit caused by overexposure of fruit tissues to solar radiation, especially when the surface temperature rises considerably above the air temperature. Direct solar radiation, particularly ultraviolet and infrared radiation, can cause a significant increase in the temperature of exposed tissues and damage to the cells of the epidermis and surface layers of the fruit. The risk increases when fruit that was normally protected by leaves is suddenly exposed due to pruning, leaf fall, defoliation, wind, water stress, or changes in fruit orientation. The exposed tissues can reach temperatures well above the ambient temperature, especially during the hottest hours of the day and under conditions of high radiation. When the surface temperature exceeds the tissue's tolerance capacity, alterations of cell membranes, protein denaturation, loss of cell function, and, in the most severe cases, localized tissue death occur. The damage can appear rapidly and does not require the presence of any infectious organism. Susceptibility depends on the species, variety, color and characteristics of the epidermis, stage of ripeness, water content, prior sun exposure, and the fruit's ability to dissipate heat. Green or immature fruits may exhibit different susceptibility than those nearing maturity, while certain varieties with darker skin may heat up more quickly. Water stress significantly increases the risk because it reduces the availability of water for transpiration and natural tissue cooling. Similarly, a sudden loss of leaf cover can expose unacclimated fruits to intense radiation. There is no infection, reproduction, or spread of a causal organism; therefore, the problem does not involve a biological transmission process and cannot spread between fruits like an infectious disease.