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A review on the successful adoption of dynamic controlled-atmosphere (DCA) storage as a replacement for diphenylamine (DPA), the chemical used for control of superficial scald in apples and pears

Prange, R. K., Wright, A. H., DeLong, J. M., Zanella, A., Zanella, A.
Acta horticulturae 2015 no.1071 pp. 389-396
apples, diphenylamine, ethanol, ethoxyquin, fearfulness, fermentation, fluorescence, industry, monitoring, oxygen, pears, plant damage, research and development, scald diseases, shelf life, British Columbia, Italy
Since the early 1960s, DPA has been the primary method to control superficial scald, a major disorder in stored apples and pears. In November 2009 the European Commission formally refused the inclusion of diphenylamine (DPA) and ethoxyquin into Annex I of Directive 91/414/EEC which lists its approved pesticides. This presentation will review the research and development of low O2-based DCA technologies as a commercial replacement for DPA. Beginning with experiments that began over 110 years ago in 1903, research showed that superficial scald in apples and pears is entirely prevented by storage in very low O2 concentrations, i.e., between 0 and 1% O2. However, some of this work indicated that low O2 fails to control or sometimes increases superficial scald. In addition, there was no reliable method to measure the lowest acceptable concentration and some research suggested that if the O2 is too low for too long, fruit damage occurs. Lastly, controlled-atmosphere (CA) room construction and control was not always sufficient to maintain adequate low O2 conditions (e.g., <1%). Therefore, the use of CA to control superficial scald was not embraced by industry. However, in the 1980s as CA room construction and gas control became more advanced, industry began testing low O2 methods to replace DPA, e.g., 0.7% O2 on ‘Delicious’ apple in British Columbia, Canada, initial low O2 stress (ILOS) (various countries) and RLOS (repeated low O2 stress with ethanol monitoring). The advent of DCA-Chlorophyll Fluorescence (DCA-CF) technology in 2001, which determines the lowest acceptable level of O2 in storage, removed the fear of fermentation and low O2 damage and gave the fruit industry more confidence to use DCA-CF (rather than DPA), for controlling superficial scald. Data will be shown on the transition to CA-based technologies to control superficial scald in the apple industry of South Tyrol, Italy, where DPA has not been used for 3 years. A new method is being tested called DCA-CF ‘Extra’ which may add extra scald prevention during shelf-life for very superficial scald-prone apples.