CHLOROPHYLL FLUORESCENCE AS A POTENTIAL INDICATOR OF CONTROLLED-ATMOSPHERE DISORDERS IN MARSHALL MCINTOSH APPLES

Chlorophyll fluorescence was evaluated as a rapid and nondestructive technique to detect low-O-2 or high-CO2 stress in apples (Malus domestica Borkh.) during storage. 'Marshall' McIntosh apples were held for 5, 10, 15, 20, or 25 days at 3C in 1) standard O-2 (2,5% to 3 %) and low CO2 (<1%), 2) low O-2 (1% to 1.5 %) and low CO2 (<l%), 3) standard O-2(2.5 % to 3 %) and standard CO2 (4% to 4.5%) or 4) standard O-2, (2.5 % to 3%) and high CO, (11% to 120/0). Only 10% of the apples had skin discoloration after 5 days in 1% to 1.5% O-2; 80% developed skin discoloration after 20 days in low O-2. Small desiccated cavities in the cortex, associated with CO2 injury, developed in 10% of the apples after 20 days in 11% to 12% CO2. Five days in 1% to 1.5% O-2 or 11% to 12% CO2 caused variable fluorescence (Fv) of apple fruit to decrease compared to those held in standard atmospheres. Additional exposure did not significantly affect Fv in either the low-O-2 (1% to 1.5%) or high-CO2 (11% to 12%) treatment. Our results suggest that chlorophyll fluorescence techniques can detect low-O-2 and high-CO2 stress in apples before the development of associated disorders.