CHLOROPHYLL FLUORESCENCE TECHNIQUES TO DETECT ATMOSPHERIC STRESS IN STORED APPLES

Abstract

Chlorophyll fluorescence was evaluated as a rapid indicator of low O 2 and high CO 2 stress in stored apples. 'McIntosh' apples were harvested in September 1994 from Nova Scotia orchards, stored in controlled atmosphere (CA, 2.5% O 2 and 4.5% CO 2 ) at 3°C for ∼5 months and then subjected to low O 2 treatments of 1%, 2%, 4% or 8% for 1, 2, 4, or 8 d at 20°C. Similarly, 'Delicious' and 'Golden Delicious' apples were harvested in October 1994, stored in CA at 0°C for ∼6 months and then subjected to high CO 2 treatments of 5%, 10% or 20% for 1, 2, 4 or 8 d at 20°C. Chlorophyll fluorescence was measured by an OS-500 Modulated Fluorometer, using the Fv/Fm test (Method 1 on fluorometer) and the Fast Actinic test (Method 4 on fluorometer). Fv/Fm was found to decrease in apples stressed with either low O 2 or high CO 2 , while T 1/2 (half-time for rise in Fv) was found to increase in the stressed apples. The effects of low O 2 or high CO 2 on Fv/Fm and T 1/2 were observed after 1 d, and this did not change with increased exposure time. Although 'Delicious' and 'Golden Delicious' apples differed in their relative fluorescence yields, both cultivars responded similarly to high CO 2 stress. Our results indicate that chlorophyll fluorescence techniques can detect low O 2 or high CO 2 stress in apples prior to the development of associated disorders, and thus has potential as a rapid and non-destructive method to screen for atmospheric stress tolerance in apples.