We evaluated regional variation in the Delta Absorbance MeterÒ index of absorbance difference (IAD) as a measure of harvest maturity and for predicting the occurrence of storage disorders in ‘McIntosh’ apples [Malus 3sylvestris (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 8C for 2 months in 2016 and 4 months in 2017. In 2016, ‘Honeycrisp’ IAD values were similar in ME and ON, but lower than in MN. In 2017, IAD 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, IAD 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 IAD 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 IAD at harvest in MN in both years and ON in 2016. Regional similarities in patterns of change in ‘Honeycrisp’ fruit IAD were not consistent from year to year, and this indicates that a single IAD standard should not be used to assess fruit maturity in different regions. In ‘McIntosh’, IAD values were variable among the three regions and were not related to other maturity indicators. IAD was not useful for measuring maturity in ‘McIntosh’ apples, but it was weakly related to core browning incidence.
Bibliographical noteFunding Information:
Received for publication 20 May 2020. Accepted for publication 7 July 2020. Published online 6 August 2020. This research was conducted as multistate project NE1336. We are grateful for funding from the Ontario Apple Growers, Canadian Horticultural Council, and the Minnesota Agricultural Experiment Station for project #MN 21-028; the Maine Agricultural & Forest Experiment Station, project #ME0-31404; and by the U.S. Department of Agriculture National Institute of Food and Agriculture. We thank Pepin Heights Orchard for their collaboration, and Hsueh-Yuan Chang, Ben Ma, and Samantha Putlak for help with assays in Minnesota. Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product, nor does it imply approval or disapproval to the exclusion of other products or vendors that may also be suitable. R.M. is the corresponding author. E-mail: rmoran@ maine.edu. This is an open access article distributed under the CC BY-NC-ND license (https://creativecommons.org/ licenses/by-nc-nd/4.0/).
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