ADDITIONAL INDEX WORDS. Malus ×domestica Borkh., chlorophyll fl uorescence, controlled atmosphere storage, dynamic low-oxygen controlled atmosphere storage, fl uorescence interactive response monitor, fruit quality, HarvestWatch, postharvest SUMMARY. HarvestWatch is a new chlorophyll fl uorescence (F)-based technology that identifi es the lowoxygen threshold for apple (Malus ×domestica) fruit in dynamic low-O 2 controlled atmosphere (DLOCA) storage environments [e.g., <1% oxygen (O 2 )]. Immediately following harvest, 'Cortland', 'Delicious', 'Golden Delicious', 'Honeycrisp', 'Jonagold' and 'McIntosh' fruit were cooled and loaded into 0.34 m 3 (12.0 ft 3 ) storage cabinets. A static controlled atmosphere (CA) regime of 1.5% O 2 , 1.5% carbon dioxide (CO 2 ) and 3 o C (37.4 o F) [0 o C (32.0 o F) for 'Delicious' and 'Golden Delicious'] was established for the control fruit, while the low-O 2 threshold was identifi ed by a spike in the fl uorescence parameter, Fα, as the O 2 levels in the DLOCA cabinets were lowered below 1%. The DLOCA storages were then maintained at O 2 levels of 0.1% to 0.2% above the threshold value for each cultivar, which returned Fα to prethreshold signatures. Quality