Alleviation of Postharvest Skin Dimpling of MN55 Apple Fruit and its Possible Association with Apple Stem Pitting Virus

Authors: TONG, CINDY - University Of Minnesota; CHANG, HSUEH-YUAN - University Of Minnesota; LUBY, JAMES - University Of Minnesota; BEDFORD, DAVID - University Of Minnesota; LOCKHART, BENHAM - University Of Minnesota; Mollov, Dimitre

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/21/2021
Publication Date: 7/28/2021
Citation: Tong, C., Chang, H., Luby, J., Bedford, D., Lockhart, B., Mollov, D.S. 2021. Alleviation of Postharvest Skin Dimpling of MN55 Apple Fruit and its Possible Association with Apple Stem Pitting Virus. HortScience. https://doi.org/10.21273/HORTSCI15847-21.
DOI: https://doi.org/10.21273/HORTSCI15847-21

Interpretive Summary: Apples are one of the most cultivated fruit trees, and the U.S. is the largest apple producer worldwide. Apples are a seasonal crop and fruit storage is widely utilized to extend their retail availability. In this research, we investigated the conditions that cause skin dimpling and scald under storage conditions. We observed that skin dimpling cannot be alleviated by chemical treatments or preconditioning fruit prior to cold storage. However, scald can be prevented if fruit is treated with diphenylamine prior to storage. Additionally, latent apple viruses, especially apple stem pitting virus (ASPV), were frequently detected in fruits from the orchard used in these experiments that developed dimpling, as well as in fruit purchased from a grocery retailer. These findings warrant further experiments to determine if viruses contribute to skin deformities in stored apples.

Technical Abstract: MN55 is an apple (Malus x 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 four months at 0-4 °C, MN55 fruit can develop several storage disorders, including skin dimpling. Skin dimpling incidence was greater for fruit harvested one week later than those harvested earlier. Dimpling cannot be alleviated by prestorage treatments of 1-methylcyclopropene or diphenylamine, or holding fruit at room temperature for one day prior to long-term cold storage. However, dimpling incidence was very low when fruit were stored at 6-7 °C. As 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 (RT-PCR) methodology, and high throughput sequencing (HTS) in peel of fruit from MN55 trees that exhibited skin dimpling after 4 months of cold storage. 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, its prevalence indicates further investigations are warranted to determine the relationship between viruses and skin deformities in stored apples.