Regional variation in the index of absorbance difference as an indicator of maturity and predictor of storage disorders in apples

We evaluated regional variation in the Delta Absorbance Meter (R) index of absorbance difference (I-AD) as a measure of harvest maturity and for predicting the occurrence of storage disorders in 'McIntosh' apples [Malus x sylvestris (L.) var. domestica (Borkh.) Mansf.] in 2016 and 'Honeycrisp' apples in 2016 and 2017. Apples were grown in Maine (ME), Minnesota (MN), and Ontario (ON), and they were harvested from one orchard in each region, and two to three times each year, followed by cold storage at 0.5 degrees C for 2 months in 2016 and 4 months in 2017. In 2016, 'Honeycrisp' I-AD values were similar in ME and ON, but lower than in MN. In 2017, I-AD was greater in ME than in the other two regions during the first harvest, and it similar to MN in the latter two harvests and lower in ON than in the other regions. In 'Honeycrisp' apples, I-AD was more strongly related to starch pattern index (SPI), internal ethylene concentration, and fruit peel blush than to chlorophyll or soluble solids concentration. Soft scald incidence (SSI) of 'Honeycrisp' fruit was greater in ME than in MN and ON in both years. In ME, SSI was related to I-AD at harvest in both years, but with an inverse relationship with the first harvest and a positive relationship in the second harvest. A positive relationship also occurred in ON in 2017. SSI was not related to I-AD at harvest in MN in both years and ON in 2016. Regional similarities in patterns of change in 'Honeycrisp' fruit I-AD were not consistent from year to year, and this indicates that a single I-AD standard should not be used to assess fruit maturity in different regions. In 'McIntosh', I-AD values were variable among the three regions and were not related to other maturity indicators. I-AD was not useful for measuring maturity in 'McIntosh' apples, but it was weakly related to core browning incidence.