Direct sunlight influences postharvest temperature responses and ripening of five avocado cultivars

Effect of direct sunlight on the postharvest behavior of five avocado (Pers ea americana Mill,) cultivars (Ettinger, Fuerte, Hass, Horshim and Pinkerto n) was examined. Probes plated 6 to 7 mm under the peel showed that the tem perature an the side exposed to the sun could be as much as 15 to 20 degree s C higher than the temperature of shade fruit, while the nonexposed side o f the fruit was approximate to 5 degrees C higher than the shade fruit. Wit h the exception of 'Ettinger', sun fruit, and especially the exposed side, were found to be most tolerant to postharvest 50 and 55 degrees C hot water treatments. Similarly, storage of fruit at 0 degrees C for between 3 to 6 weeks caused severe chilling injury to shade fruit, with less effect on sun fruit, Furthermore, there was little or no damage on the exposed side of t he sun fruit. During postharvest ripening at 20 degrees C, sun fruit showed a delay of between 2 to 5 days in their ethylene peak compared with shade fruit, The exposed side of the sun fruit was generally firmer than the none xposed side, and the average firmness was higher than that of shade fruit. Activities of polygalacturonase and cellulase were similar in shade and sun fruit of similar firmness, After inoculation with Colletotrichum gloeospor ioides (Penz) Penz@sacc, the appearance of lesions on sun fruit occurred 2 to 3 days after shade fruit. Levels of heat-shock proteins mere examined us ing western blotting with antibodies for Class I and II cytoplasmic heat-sh ock proteins. Class I reacted with proteins from the exposed side of sun fr uit and Class II with proteins from both sides of sun fruit, Thus, it is de ar that preharvest exposure of fruit to the sun can result in a wide range of postharvest responses.