DA Meter Readings and Chlorophyll Content on the Blushed and Unblushed Sides of Nine Apple Cultivars

The DA meter is a non-destructive method to determine chlorophyll content of fruit, and may have utility as an additional harvest index for apple fruit. In this study, I_DA and chlorophyll concentration of blushed and unblushed skins of ‘SnapDragon’, ‘RubyFrost’, ‘Cortland’, ‘Fuji’, ‘Honeycrisp’, ‘Jonagold’, ‘Mutsu’, ‘RedMax McIntosh’ and ‘Redcort’ was measured. With the exception of ‘Mutsu’ and ‘Fuji’, more than half of the fruit of each cultivar had I_AD values that were higher on the blushed side compared with the unblushed side. I_AD values correlated with chlorophyll a and total chlorophyll but not chlorophyll b. The correlation between I_AD and chlorophyll a was greater on the blushed side of the fruit in six of the cultivars.  The average I_AD value for each fruit was associated with internal ethylene concentration and starch index in fruit of some cultivars. In summary, the difference in I_AD values and their relationship with chlorophyll levels from the blushed and unblushed side of the fruit can be significant and is cultivar dependent.  I_AD values may relate to harvest maturity, but its usefulness across orchard lots requires further investigation.