Superficial Scald Development and Related Metabolism is Modified by Postharvest Light Irradiation

Authors: Rudell, David; Mattheis, James

Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/7/2008
Publication Date: 12/5/2008
Citation: Rudell Jr, D.R., Mattheis, J.P. 2008. Superficial Scald Development and Related Metabolism is Modified by Postharvest Light Irradiation. Postharvest Biology and Technology. 51:174-182.

Interpretive Summary: Development of superficial scald (scald) of susceptible apple cultivars is exacerbated by low light exposure during the growing season. Global metabolic profiling was used to evaluate diverse peel metabolites from ‘Granny Smith’ apples bagged on the tree then exposed to artificial UV-white light after harvest. Fruit were air-stored at 1 oC for 6 months and then held for 4 days at 20 oC. Scald was eliminated on the side of the fruit exposed to artificial light and reduced on the unexposed side, where light was limited, with increasing light treatment duration. Principal component analysis (PCA) of the peel metabolome revealed associations among scald status, light treatment duration, and individual metabolites from multiple pathways including many from the isoprenoid and phenylpropanoid pathways. Regression analysis of metabolites selected using the PCA model was used to verify these associations. Although accumulation patterns were atypical of those found in peel on the exposed side of the fruit, levels of hyperin, reynoutrin, avicularin, catechin, and (-) epicatechin increased in unexposed peel and decreased with increased scald severity. a-Farnesene and 2,6,10-trimethyldodeca-2,7(E),9(E),11-tetraen-6-ol (TMDtol) content diminished with light treatment duration on the exposed side while squalene levels increased. a -Tocopherol levels increased with light treatment duration on the unexposed side but decreased as scald severity increased. Given the antioxidant nature of these metabolites, associations indicate a number of light-enhanced metabolites that may impact scald incidence and severity. Sunlight can positively or negatively alter apple fruit appearance affecting its marketability. Incidence of superficial scald, a necrotic storage disorder of apple, is reduced on portions of apple peel exposed to sunlight in the orchard. Using sophisticated analytical equipment coupled with statistical data-mining techniques, metabolic alterations in apple peel pathways related to superficial scald were detected and characterized following light exposure and long-term cold storage. These results demonstrate that multiple metabolic pathways are associated with superficial scald incidence and severity. Understanding these relationships could lead to the development and employment of molecular markers for produce management and breeding assistance.

Technical Abstract: Development of superficial scald (scald) of susceptible apple cultivars is exacerbated by low light exposure during the growing season. Global metabolic profiling was used to evaluate diverse peel metabolites from ‘Granny Smith’ apples bagged on the tree then exposed to artificial UV-white light after harvest. Fruit were air-stored at 1 oC for 6 months and then held for 4 days at 20 oC. Scald was eliminated on the side of the fruit exposed to artificial light and reduced on the unexposed side, where light was limited, with increasing light treatment duration. Principal component analysis (PCA) of the peel metabolome revealed associations among scald status, light treatment duration, and individual metabolites from multiple pathways including many from the isoprenoid and phenylpropanoid pathways. Regression analysis of metabolites selected using the PCA model was used to verify these associations. Although accumulation patterns were atypical of those found in peel on the exposed side of the fruit, levels of hyperin, reynoutrin, avicularin, catechin, and (-) epicatechin increased in unexposed peel and decreased with increased scald severity. a-Farnesene and 2,6,10-trimethyldodeca-2,7(E),9(E),11-tetraen-6-ol (TMDtol) content diminished with light treatment duration on the exposed side while squalene levels increased. a -Tocopherol levels increased with light treatment duration on the unexposed side but decreased as scald severity increased. Given the antioxidant nature of these metabolites, associations indicate a number of light-enhanced metabolites that may impact scald incidence and severity.