Comparative analysis of metabolic differences between sunburn and sunscald disorder on 'Packham’s triumph’ pear

Authors: YOO, JINGI - Washington State University; SEPULVEDA, GLORIA - Washington State University; Rudell, David; TORRES, CAROLINA - Washington State University

Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/9/2022
Publication Date: 10/15/2022
Citation: Yoo, J., Sepulveda, G., Rudell Jr, D.R., Torres, C. 2022. Comparative analysis of metabolic differences between sunburn and sunscald disorder on 'Packham’s triumph’ pear. Postharvest Biology and Technology. 195. Article 112153. https://doi.org/10.1016/j.postharvbio.2022.112153.
DOI: https://doi.org/10.1016/j.postharvbio.2022.112153

Interpretive Summary: Sunscald can be a prominent source of postharvest loss of apples and pears in many of the world’s key growing regions. Identification of this issue in pears is relatively new in the U.S. and may be a consequence of warmer growing seasons. We identified a chemical “fingerprint” to distinguish this from other postharvest disorders with similar symptoms. The chemical fingerprint distinguishes symptoms from pre-harvest sunburn and healthy tissue and is indicative of widespread physiological changes leading to symptom development. This is another step in a multi-year effort to differentiate disorders with similar symptoms to prevent misdiagnosis from leading to improper mitigation steps and crop losses.

Technical Abstract: 4. Sunburn and sunscald are common apple and pear peel disorders. Although both disorders are caused by excessive sunlight exposure, sunburn appears in the orchard, whereas sunscald gradually develops during cold storage. Despite having been well characterized and studied in apples, these disorders are still poorly understood in pears. Here we performed comparative metabolomic analyses on pears with different levels of sunburn and sunscald incidences to understand metabolic changes associated with sun damage. Fruit from different orchards were classified according to sunburn levels (mild, moderate, and severe) at commercial harvest and sunscald incidence and severity (mild, moderate, and severe) after 6 months in cold storage. Peel samples were collected from both healthy and damaged sections of each category for metabolic profiling. A total of 379 primary and secondary metabolites were evaluated, among which 260 and 278 were found to have different levels between sunburned and sunscalded peel, respectively, compared with healthy tissues. Elevated levels of 76 metabolites were found in sunburn and 144 metabolites in sunscald. Sunburn severity correlated with levels of photosystem-related metabolites, while sunscalded tissue had higher levels of diacylglycerides, pentacyclic triterpenoic acids, and a-amyrin acyl esters. Content of some fatty acids and volatile alcohols was elevated in both disorders. We expect that our results provide a means for distinguishing these physiological disorders on European pears, which may occur more frequently due to increasing seasonal temperatures in many of the world’s key pear growing regions.