Abstract:

The content and ratio of mineral elements, including Ca, K, Mg and P in fruit flesh, peel and apoplast of the normal and bitter pit fruit, were studied with the aim to explore the mechanism of bitter pit occurrence in ‘Fuji’ apple at harvest stage. The results showed that the fruits with bitter pit had higher fruit weight and soluble solids content compared with the normal fruits. No significant difference was found in fruit firmness, malic acid content and fruit shape index between bitter pit fruit and normal fruit. Moreover, there was no significant difference in the apoplastic Ca content among the normal fruit, the normal parts and the scab parts of bitter pit fruit. However, the apoplastic contents of K, Mg and P in scab parts of bitter pit fruit were higher than those in the normal part of bitter pit fruit and the normal fruit. The analysis of the ratios between different mineral elements showed that the scab parts of bitter pit fruit had higher ratio of K/Ca, Mg/Ca, P/Ca and [K+Mg]/Ca, which was 1.64, 1.50, 2.05 and 1.63 times that of normal fruits respectively. The results also indicated that the Ca content of peel and flesh in bitter pit fruit were much lower than those in the normal fruit, and the contents of K, Mg, P and N in bitter pit fruit were higher than those in the normal fruit. Moreover, the ratios of K/Ca, Mg/Ca, P/Ca, [K+Mg]/Ca and N/Ca in the scab sites of bitter pit fruit were significantly higher than those in normal apple fruit. It is concluded that the occurrence of bitter pit in apple fruit is not only related to the content of Ca in the fruit, but also highly related to the content of K, Mg, P and N and the ratio of K/Ca, Mg/Ca, P/Ca, [K+Mg]/Ca and N/Ca. Therefore, balanced nutrition and scientific fertilization are the key management points to solve bitter pit occurrence in apple cultivation.

Key words: apple fruit, bitter pit, apoplast, mineral element, quality