USING VOLATILE EMISSIONS AND CHLOROPHYLL FLUORESCENCE AS INDICATORS OF HEAT AND FREEZING INJURY IN APPLE FRUITS

Volatile emissions and chlorophyll fluorescence were investigated as signals of freezing and heat injury for apple ( Malus x domestica Borkh.) fruit. McIntosh, Cortland, Northern Spy, and Jonagold apples were held at -8.5°C for 0, 6, 12 or 24 hours (freezing treatments), or at 46°C for 0, 4, 8 or 12 hours (heat treatments). Following treatments, fruit were kept at 20°C and evaluated after 1, 2, 4, and 7 days. Heat and freezing treatments induced volatiles such as ethanol, acetaldehyde, ethyl acetate, butanol, hexanol and ethyl-related esters. The 12 and 24 hours freezing and the 8 and 12 hours heat treatments increased ethanol and ethyl acetate production in all 4 cultivars by as much as 170- and 30- fold, respectively, one day after treatments. These treatments also reduced ethylene production and chlorophyll fluorescence. Freezing for 24 hours and heat for 12 hours caused serious flesh browning. Among the cultivars investigated, Northern Spy and McIntosh were the most sensitive to freezing and heat stress based on internal injury. The degree of increase in stress-induced volatile emissions such as ethanol and decrease in chlorophyll fluorescence correlated with severity of stress-induced injury.