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

Sunburn and sunscald are common apple and pear peel disorders. Although both disorders are caused by excessive sunlight exposure, sunburn occurs in the orchard, whereas sunscald develops progressively during storage periods. 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 their sunburn severity (light, moderate, and severe) at commercial harvest and later, sunscald level (light, moderate, and severe) after cold storage for 6 months. Peel samples were collected from both damaged and healthy sections of each class for metabolic profiling. From a total of 379 primary and secondary metabolites, 260 and 278 were found to have different accumulation levels between sunburned and sunscalded peel, respectively, compared to healthy tissues. Sunburn severity was positively correlated with the level of photosystem-related metabolites, while sunscald was with diacylglycerides, alpha-amyrin acyl esters, and pentacyclic triterpenoic acids. The content of some volatiles and fatty acids were elevated in both disorders. Our results provide biochemical information to distinguish these physiological disorders on pears, which may occur more frequently in the future due to increasing seasonal temperatures in many pear growing regions in the world due to climate change.