Background: 'Honeycrisp' is an apple cultivar that is susceptible to soft scald, a chilling injury expressed as necrotic patches on the peel. Improved understanding of metabolism associated with the disorder would improve our understanding of soft scald and contribute to developing more effective management strategies for apple storage. It was expected that specific gene expression and specific metabolite levels in the peel would be linked with soft scald risk at harvest and/or specific time points during cold storage. Results: Fruit from nine 'Honeycrisp' apple orchards that would eventually develop different incidences of soft scald between 4 and 8 weeks of cold air storage were used to contrast and determine differential transcriptomic and metabolomic changes during storage. Untargeted metabolic profiling revealed changes in a number of distinct pathways preceding and concurrent with soft scald symptom development, including elevated γ-aminobutryic acid (GABA), 1-hexanol, acylated steryl glycosides, and free p-coumaryl acyl esters. At harvest, levels of sesquiterpenoid and triterpenoid acyl esters were relatively higher in peel of fruit that did not later develop the disorder. RNA-seq driven gene expression profiling highlighted possible involvement of genes and associated metabolic processes with soft scald development. These included elevated expression of genes involved in lipid peroxidation and phenolic metabolism in fruit with soft scald, and isoprenoid/brassinosteroid metabolism in fruit that did not develop soft scald. Expression of other stress-related genes in fruit that developed soft scald included chlorophyll catabolism, cell wall loosening, and lipid transport while superoxide dismutases were up-regulated in fruit that did not develop the disorder. Conclusions: This study delineates the sequential transcriptomic and metabolomic changes preceding soft scald symptom development. Changes were differential depending on susceptibility of fruit to the disorder and could be attributed to key stress related and mediating pathways.

BackgroundInconsistent pear fruit ripening resulting from variable harvest maturity within tree canopies can contribute to postharvest losses through senescence and spoilage that would otherwise be effectively managed using crop protectant and storage regimes. Because those inconsistencies are likely based on metabolic differences, non-targeted metabolic profiling peel of ‘d’Anjou’ pears harvested from the external or internal canopy was used to determine the breadth of difference and link metabolites with canopy position during long-term controlled atmosphere storage.ResultsDifferences were widespread, encompassing everything from expected distinctions in flavonol glycoside levels between peel of fruit from external and internal canopy positions to increased aroma volatile production and sucrose hydrolysis with ripening. Some of the most substantial differences were in levels of triterpene and phenolic peel cuticle components among which acyl esters of ursolic acid and fatty acyl esters of p-coumaryl alcohol were higher in the cuticle of fruit from external tree positions, and acyl esters of α-amyrin were elevated in peel of fruit from internal positions. Possibly the most substantial dissimilarities were those that were directly related to fruit quality. Phytosterol conjugates and sesquiterpenes related to elevated superficial scald risk were higher in pears from external positions which were to be potentially rendered unmarketable by superficial scald. Other metabolites associated with fruit aroma and flavor became more prevalent in external fruit peel as ripening progressed and, likewise, with differential soluble solids and ethylene levels, suggesting the final product not only ripens differentially but the final fruit quality following ripening is actually different based on the tree position.ConclusionsGiven the impact tree position appears to have on the most intrinsic aspects of ripening and quality, every supply chain management strategy would likely lead to diverse storage outcomes among fruit from most orchards, especially those with large canopies. Metabolites consistently associated with peel of fruit from a particular canopy position may provide targets for non-destructive pre-storage sorting used to reduce losses contributed by this inconsistency.Electronic supplementary materialThe online version of this article (10.1186/s12870-018-1544-6) contains supplementary material, which is available to authorized users.