Chlorophylls, carotenoids and anthocyanin concentrations in the skin of ‘Gala’ apples during maturation and the influence of foliar applications of nitrogen and magnesium

Abstract

‘Gala’ apple fruit were sampled over two growing seasons, to determine the effects of maturation, and of foliar applications of nitrogen and magnesium on pigment concentrations and colour development in maturing fruit. Treatments of urea and/or magnesium sulphate sprays were applied to the trees in a commercial orchard. The chlorophyll, carotenoid and anthocyanin concentrations in the fruit skin were determined for both the blush and back sides over 15 harvests in 1991–1992. In 1990–1991, the skin chlorophyll concentrations were determined only for the back side of the fruit. The fruit nitrogen, magnesium and sulphur concentrations were determined near maturity. The concentrations of chlorophyll and carotenoids in apple skin decreased from the first harvest in 1991–1992 as the fresh weight increased from 12 g, 40 days from flowering to 140 g, 138 days from flowering. Chlorophyll continued to decrease whereas carotenoid concentrations increased after 138 days and until at least 153 days. The average skin chlorophyll and carotenoid concentrations were higher on the blush side of the fruit than on the back. The total chlorophyll per fruit increased from the first harvest to a peak about 70 days after flowering in 1990–1991 and then decreased over the remainder of the period studied. The time of this peak was about 40 days later in the 1991–1992 season compared with the 1990–1991 season. The total carotenoid increased up to about 50 days after flowering in 1991–1992, fluctuated and then decreased up to 138 days when the amount increased again. The ratio of carotenoids to chlorophylls was highest for the first three harvests, fluctuated somewhat up to c 138 days after flowering after which the ratio increased rapidly. The anthocyanin concentrations were low and fluctuated up to 130 days from flowering and then increased markedly only on the blush side at 130 days, about 14 days before the carotenoids started to increase. The treatment of the tree canopy with urea increased the chlorophyll and carotenoid concentrations in the fruit skin, 14–20 days after the first application until after maturity, more so on the blush side than on the back side. These increased concentrations were maintained up to the harvest after which carotenoid concentrations increased. The urea treatment lessened the increase of anthocyanin concentrations in the blush side skin of the fruit, at maturity. At maturity, the nitrogen concentration of fruit from urea treated trees was higher than those from untreated trees. The magnesium sulphate treatment of the canopy increased the chlorophyll and carotenoid concentration on the back of the fruit within 20–30 days from commencing spraying. The ‘ground colour’ scores for the back sides of the fruit (used for fruit picking and grading) were greener for the urea treated fruit and reached an acceptable score about two weeks later than the untreated fruit. ©1998 SCI