BACKGROUND
Apple is one of the staple fruits worldwide, which are a good source of mineral nutrients. However, little is known about genetic variation for mineral nutrition in apple germplasm. In this study, we report on the assessment of calcium and zinc contents in mature fruits of 378 apple cultivars and 39 wild relatives. Mineral concentrations were quantified using flame atomic absorption spectroscopy (FAAS).

RESULTS
Both calcium and zinc accumulation showed great variation among accessions tested. Overall, wild fruits were significantly richer in zinc than cultivated fruits, whilst the average concentration of calcium was similar between cultivated and wild fruits. The difference in zinc concentration between wild and cultivated fruits may be an indirect result of artificial selection on fruit characteristics during apple domestication. Moreover, calcium concentration in fruit showed a decrease trend throughout fruit development of apple, whilst zinc concentration in fruit displayed a complex variation pattern in the late stages of fruit development.

CONCULSION
The finding of a wild genetic variation for fruit calcium and zinc accumulation in apple germaplsm could be helpful for future research on genetic dissection and improvement of calcium and zinc accumulation in apple fruit.