CHLOROPHYLLS, CAROTENOIDS AND ANTHOCYANIN CONCENTRATIONS IN THE SKIN OF GALA APPLES DURING MATURATION AND THE INFLUENCE OF FOLIAR APPLICATIONS OF NITROGEN AND MAGNESIUM

'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 maturin g fruit. Treatments of urea and/or magnesium sulphate sprays were appl ied to the trees in a commercial orchard. The chlorophyll, carotenoid and anthocyanin concentrations in the fruit skin were determined for b oth the blush and back sides over 15 harvests in 1991-1992. In 1990-19 91, the skin chlorophyll concentrations were determined only for the b ack side of the fruit. The fruit nitrogen, magnesium and sulphur conce ntrations were determined near maturity. The concentrations of chlorop hyll and carotenoids in apple skin decreased from the first harvest in 1991-1992 as the fresh weight increased from 12 g, 40 days from flowe ring to 140 g, 138 days from flowering. Chlorophyll continued to decre ase whereas carotenoid concentrations increased after 138 days and unt il at least 153 days. The average skin chlorophyll and carotenoid conc entrations 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 o ver the remainder of the period studied. The time of this peak was abo ut 40 days later in the 1991-1992 season compared with the 1990-1991 s eason. The total carotenoid increased up to about 50 days after flower ing in 1991-1992, fluctuated and then decreased up to 138 days when th e 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 ant hocyanin concentrations were low and fluctuated up to 130 days from fl owering and then increased markedly only on the blush side at 130 days , about 14 days before the carotenoids started to increase. The treatm ent of the tree canopy with urea increased the chlorophyll and caroten oid concentrations in the fruit skin, 14-20 days after the first appli cation until after maturity, more so on the blush side than on the bac k side. These increased concentrations were maintained up to the harve st 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 concentrati on of fruit from urea treated trees was higher than those from untreat ed trees. The magnesium sulphate treatment of the canopy increased the chlorophyll and carotenoid concentration on the back of the fruit wit hin 20-30 days from commencing spraying. The 'ground colour' scores fo r the back sides of the fruit (used for fruit picking and grading) wer e greener for the urea treated fruit and reached an acceptable score a bout two weeks later than the untreated fruit.