BACKGROUND: Sorbitol is the major sugar alcohol in apple and its accumulation in fruit is associated with fruit sweetness. However, little is known about variation in sorbitol content in fruits of apple germplasm. In this study, we investigated sorbitol content in mature fruits of 243 apple cultivars and 20 wild relatives using high-performance liquid chromatography (HPLC).
RESULTS: Sorbitol accumulation showed a significant variation in apple germplasm. Overall, cultivated fruits had significantly lower content of sorbitol than wild fruits. Fruit sorbitol concentration was significantly correlated with fruit size and acidity that are extensively domesticated traits. Hence, the variation in sorbitol accumulation between cultivated and wild fruits may be the indirect result of fruit size and acidity selection during domestication. Moreover, sorbitol content was maintained at low levels throughout fruit development, with a dramatic decrease at the middle stage. The SDH1 gene was highly expressed throughout fruit development, and its expression showed a significant correlation with fruit sorbitol concentration, suggesting its potential role in apple fruit sorbitol accumulation.