Evaluating the Synchronicity of Flesh and Peel Ripening in Standard and New Cultivars of Apples

Generally internal ethylene concentration (IEC) and starch clearing index (SCI) are used to evaluate apple maturity for harvest in North America. These two methods provide good information on the flesh maturation of apples. Chlorophyll decline in apple peel was recognized as a potential criterion for maturity assessment in the early 1990s, but has not been practical to use because of the time required to extract chlorophyll from the peel. Recently, non-destructive instruments measuring apple peel chlorophyll using spectral reflectance of two chlorophyll-related near infrared bands has enabled instantaneous assessment of peel chlorophyll and thus allows interpretation of maturity. In this study, ‘Royal Gala', ‘Golden Delicious', ‘Fuji (strain Nagano 1)', Aurora Golden Gala™, Nicola™, SPA493, and SPA365 were monitored for changes in IEC, SCI, and chlorophyll content during maturation in Fall 2011. Decline in chlorophyll content was linear with advance in maturity for all cultivars tested. In most cultivars of apples tested, the IEC, SCI, and chlorophyll changes were well synchronized. This indicates that that non-destructive chlorophyll assessment may be an alternate tool for monitoring apple maturation and could also enable mapping of orchards to improve uniformity of maturity at harvest. In some apples, however, changes in chlorophyll content were not well synchronized with IEC and SCI changes. For an apple such as ‘Fuji', it may mean that the harvest criteria using non-destructive technology should be adjusted specifically for that cultivar. In other cultivars, for which peel and flesh maturation is even more asynchronous, at least in Fall 2011, suggesting that there may be concerns for maturation in those cultivars that need further investigation.