Written by Bill Wolk, BC Tree Fruit Cooperative; and Peter Toivonen, Agriculture and Agri-Food Canada; Prepared by Ines Hanrahan August 2020.
To date, Ambrosia maturity has largely been determined by starch index. The general recommendation is to start harvest at a starch of 2.6 and finish by 4.4 on the Cornell starch chart (pictured below) (1-8, translates to 0% core stain, 75-100% core stain).
Because Ambrosia’s climacteric generally occurs after the fruit has been harvested, starch is sometimes not as well correlated with maturity as it is in other varieties. Work in British Columbia (Toivonen, 2015; Toivonen et al., 2016) indicates that IAD values determined with a DA meter can be more highly correlated with maturity and post-storage firmness than starch values, provided the proper protocol is used with the meter. The DA meter should be fitted with a light shroud that blocks extraneous sunlight and ensures accurate readings. DA meter readings are taken on fruit on the tree at mid-canopy height, not outside of the canopy or in deep shade. An average IAD should be determined from single readings on 30 fruit. Readings should not be taken on either the blush or shade face of the fruit but, instead, on the side of the fruit at the margin between the blush and shade faces. For long term storage, Ambrosia should be harvested with average IAD readings of 0.70 to 0.50. Shorter-term fruit should be finished by 0.30.
Ambrosia benefits greatly from 1-MCP treatment. Without 1-MCP, Ambrosia can become mealy after four or more months in storage. Because its climacteric develops slowly, 1-MCP can have a beneficial effect over a range of harvest starch or IAD values.
Ambrosia is a chilling sensitive variety. Fruit harvested at more advanced maturity is increasingly susceptible to soft scald and/or soggy breakdown. Temperature conditioning is used to mitigate the effects of chilling. Hold Ambrosia at 35°F for a week to ten days immediately after harvest and then store at 33°F. Controlled atmosphere storage recommendations are provided in table 1 below.
Table 1. Recommended CA Storage Parameters.
| Temperature | Oxygen | Carbon Dioxide | ||||
| °C | °F | Target | Range | Target | Range | |
| 1st 7-10 days | 1.7 | 35 | 1.2% | 1.0-1.4% | 1.5% | 1.3-1.7% |
| After 10 days | 0.6 | 33 | 1.2% | 1.0-1.4% | 1.5% | 1.3-1.7% |
References
Toivonen, P.M.A. 2015 Comparison of IAD and starch-iodine indices at harvest and how they relate to post-storage firmness retention in Ambrosia apples over three growing seasons. Can. J. Plant Sci. 95: 1177-1180.
Toivonen, P.M.A., Lu, C., and Lannard, B. 2016. Visible spectroscopy IAD measures in apple: impact of stress and shading on maturity indexing. Acta Hortic. 111: 243-250.
Contacts
Ines Hanrahan, Managing Director, Washington Tree Fruit Research Commission, Yakima, WA; office: 509-574-1595; mobile: 509-699-0267; hanrahan@treefruitresearch.com
Bill Wolk, BC Tree Fruits Cooperative, Oliver BC, Canada; office: 250-498-3491; mobile: 250-490-7357; bwolk@btree.com
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