Nitrogen management is critical for achieving high yield and good fruit quality in commercial apple production (Sanchez et al., 1995) because tree growth, fruit yield, and quality are dependent on N supply. Within a certain range of N supply, increasing N supply leads to larger fruit and higher soluble solids in ‘Gala’ apple (Xia et al., 2009). However, red-fruited cultivars grown under high N supply often have poor color.
The intensity and extent of coloration is an important consideration in determining harvest time for red-fruited apple cultivars. Early work by Magness et al. (1940) showed a negative relationship between leaf N content and fruit skin color in ‘Rome Beauty’ apple. Since then, it has been reported in many studies that fruit coloration decreases as the rate of N application increases (Fallahi et al., 2001, 2006; Saito, 1995; Week et al., 1952). This decrease in coloration with increasing N application is presumably caused by the inhibition of N on anthocyanin synthesis and accumulation. However, delayed chlorophyll degradation might have also contributed. Higher rates of N were associated with greener fruit in ‘Golden Delicious’ (Meheriuk et al., 1992; Neilsen et al., 1984).
Although the effect of N supply on coloration of apples has been well documented, much less attention has been paid to its effect on other aspects of fruit maturity. Because maturity at harvest greatly affects apple fruit quality and storage performance, starch hydrolysis indices (starch content), soluble solids concentration (SSC), flesh firmness, and the rate of ethylene evolution are often measured in addition to skin color to indicate the maturity stage of apple for making decisions on harvest time. N supply does not necessarily affect all the fruit maturity indices in the same manner. High N application was found to enhance preharvest fruit drop of ‘McIntosh’ apples (Hoffman, 1940). High N application was later reported to enhance ethylene evolution and respiration of ‘Fuji’ apple at harvest (Fallahi et al., 2001) and ethylene evolution of ‘Starkspur Golden Delicious’ apple after cold storage (Fallahi et al., 1985). Neilsen et al. (2006) observed that ‘Gala’ apple trees receiving low N supply at 0 to 4 weeks after bloom had lower starch index (higher starch) in fruit at harvest than those receiving high N supply during the same period or low N supply at later times. Fallahi et al. (2001) also noticed that ‘Fuji’ apple trees receiving low N supply had a slightly lower starch index (slightly higher starch) than those at higher N supply. All these observations suggest that fruit maturity might be advanced by high N supply. The objective of this study was to determine the effects of N supply on flesh starch degradation relative to the skin pigmentation in ‘Gala’ apple.
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