Multiple types of flesh browning can occur as storage disorders in ‘Honeycrisp’ apple (Malus ×domestica Borkh.) fruit. Predicting its occurrence is hindered by differing definitions of the types of browning, incomplete understanding of their etiologies, and difficulty in assessing harvest maturity of ‘Honeycrisp’ fruit. In 2013, of ‘Honeycrisp’ fruit grown, harvested over multiple weeks, and stored in Maine, Minnesota, Ontario, and Quebec, only the Quebec fruit developed diffuse flesh browning. A detailed comparison showed that the Quebec fruit differed in size, but not in other quality attributes, from fruit of the other locations. The Quebec fruit experienced lower temperatures during active fruit growth and were increasing in cell size up to harvest. Analyses of climate data from 2009 to 2015 indicated that accumulated growing degree-days (GDD) 50–60 day after full bloom (DAFB) could account for 31% of the variation in diffuse flesh browning, and seasonal GDD <500 are associated with a greater likelihood of injury. Fruit that exhibited diffuse flesh browning had higher magnesium and lower fructose levels than unaffected fruit. As these measurements were made after browning was assessed, the timing of the onset of these characteristics in relation to browning cannot be determined.
Cindy B.S. Tong, Hsueh-Yuan Chang, Jennifer K. Boldt, Yizhou B. Ma, Jennifer R. DeEll, Renae E. Moran, Gaétan Bourgeois, and Dominique Plouffe
Cindy B.S. Tong, Hsueh-Yuan Chang, James J. Luby, David Bedford, Benham E.L. Lockhart, Roy G. Kiambi, and Dimitre Mollov
MN55 is an apple (Malus ×domestica Borkh.) cultivar recently released by the University of Minnesota apple breeding program, with fruit marketed in the U.S. as Rave®. When stored for 4 months at 0 to 4 °C, MN55 fruit can develop several storage disorders, including skin dimpling. Skin dimpling incidence was greater for fruit harvested 1 week later than those harvested earlier. Dimpling was not alleviated by prestorage treatments of 1-methylcyclopropene or diphenylamine or by holding fruit at room temperature for 1 day before long-term cold storage. However, dimpling incidence was very low when fruit were stored at 6 to 7 °C. Because viruses have been implicated in other fruit dimpling disorders, the presence of viruses in MN55 leaves and fruit was studied. Apple stem pitting virus (ASPV) was detected by microscopy, reverse transcriptase polymerase chain reaction (RT-PCR) methodology, and high throughput sequencing (HTS) in peel of fruit from MN55 trees that exhibited skin dimpling after 4 months of storage at 0 to 1 °C. ASPV was also detected in supermarket-purchased fruit of other cultivars with noticeable skin dimpling. Although ASPV was not conclusively demonstrated to cause skin dimpling in our work, its prevalence indicates that further investigations are warranted to determine the relationship between viruses and skin deformities in stored apples.