Ethylene Biosynthesis and Fruit Color Development in `Pink Lady' Apples during Growth and Maturation

Abstract

Growth and maturation of `Pink Lady' (Malus domestica Borkh.) apples with special emphasis on ethylene biosynthesis and color development were monitored in Western Australia during 2002-2003. Changes in fruit growth, respiration rate, ethylene production, anthocyanin accumulation and development of red blush were evaluated between 60 days after full bloom (DAFB) and commercial harvest (191DAFB). Fruit diameter, length and fresh weight showed the typical single sigmoid growth curve, with linear increases until 158 DAFB. High respiration rate and ethylene production were recorded 60 DAFB followed by rapid decrease until 144 DAFB and then a steady increase, which peaked between 172 and 179 DAFB. Red blush on the fruit surface showed steady increase from 167 DAFB and corresponded to concomitant decrease in hue angle. Total anthocyanin increased from 167 DAFB till harvest and synchronized with increasing ethylene and maturity of apples. There were significant (P ≤ 0.001), direct linear relationships between ethylene production and total anthocyanin (r = 0.63, y = 7.6032x + 2.4756), total anthocyanin and red blush (r = 0.74, y = 0.5082x -1.54). Significant (P ≤ 0.001) negative direct linear relationships between total anthocyanin and hue angle (r = -0.89, y = -0.5973x + 110.14), and ethylene and hue angle (r = -0.69, y = -5.37x + 109.60) were recorded. Increasing anthocyanin content and red blush also coincided with decreasing daily temperatures in the orchard. Reduction in fruit firmness and acidity and increase in TSS from 167DAFB were good indicators of advancing maturity of apples. Our experimental results indicate that red blush in `Pink Lady' apples develops a few weeks before harvest and is regulated by ethylene biosynthesis and temperature.