REDUCING EXTERNAL CHILLING INJURY IN STORED HASS AVOCADOS WITH DRY HEAT-TREATMENTS

'Hass' avocados (Persea americana Mill.) were heated in air at 25 to 4 6C for 0.5 to 24 hours and stored at 0, 2, or 6C, After storage, fruit were ripened at 20C and their quality was evaluated, In unheated frui t, external chilling Injury occurred in fruit stored at 0 or 2C, but n ot 6C. Chilling injury was also evident after storage at 2C in fruit h eated at 34C, and to a lesser extent in fruit heated at 36C. A heat tr eatment (HT) of 38C for 3, 6, or 10 hours and 40C for 0.5 hour further reduced external chilling injury induced by storage at 2C. These HTs did not reduce internal fruit quality and resulted in more marketable fruit than unheated fruit stored at 6C. Low-temperature storage and HT slowed avocado ripening, resulting in longer shelf life after storage , In flesh tissue sampled directly after selected HTs, the levels of m RNA homologous to cDNA probes for two plant heat-shock protein (HSP) g enes (HSP17 and HSP70) increased to a maximum at 40C and declined at h igher temperatures. These increases in gene expression coincided with the extent to which HTs prevented chilling injury. Hot-air HTs confer significant protection against low-temperature damage to avocados.