Preharvest exposure to the sun influences postharvest responses of ‘Hass’ avocado fruit

Abstract

‘Hass’ avocados (Persea americana Mill.) exposed to direct sunlight (sun fruit) had diurnal temperature cycles with flesh tissue reaching as high as 43°C under ambient temperatures of 15–25°C. The response of sun and shaded fruit to postharvest treatments differed significantly. External damage from hot water treatments of 50°C for up to 10 min, was lower in sun fruit, particularly on the exposed side of the fruit. Similarly, while shaded fruit had high levels of external chilling injury when stored at 0.5°C for up to 28 days, the exposed side of the fruit was undamaged. Leakage of electrolytes from skin tissue from the exposed side of sun fruit did not increase during storage, while that from shaded fruit increased by about 60%. In addition, for fruit ripened without storage, sun fruit took longer to ripen than shade fruit. Changes in heat shock protein (hsp) gene expression and specific protein bands reflected the diurnal temperature cycle, with up-regulation of hsp mRNA and synthesis of specific proteins at flesh temperatures >30°C. Thus, exposure of fruit to the sun results in high skin and flesh temperatures, and consequently reduced incidence of postharvest heat and chilling injuries. These beneficial effects are similar to those found following postharvest heat treatments.