2018 ASHS Annual Conference

Intense sun stress in the apple-growing region of eastern Washington state can cause delayed sunscald, a superficial postharvest peel browning disorder occurring on the sun-exposed side of apples. There is no known treatment for delayed sunscald once it occurs, so early detection of this disorder is key to avoiding losses. Polar, non-polar, and volatile metabolite extractions were performed to identify changes in peel chemistry associated with sun-induced injury prior to and during cold storage. Samples were collected from the sun-exposed and unexposed sides of the apple at harvest and at multiple timepoints throughout cold storage: 2 weeks, 1, 2, 4, 5, and 6 months. In addition, severely sunscalded peel was also collected for comparison. A principle component analysis and 2-way ANOVA was performed using Metaboanalyst, and a pairwise correlation network was generated using WGCNA, Cytoscape, and Allegro to visualize the multidimensional metabolome. Results indicated that p-coumaryl esters were higher on the sun-exposed side, indicating changes in cuticle consistency. Vinyl aldehydes and quercetin glycosides were more abundant on the sun-exposed side of the apple, consistent with their previously reported roles in sun stress, making these metabolites potential targets for early detection of delayed sunscald. Now that we have selected potential metabolic targets for delayed sunscald, a next step would be to utilize properties of these metabolites to more easily and economically detect delayed sunscald prior to symptom development.