Non-destructive maturity assessment of 'Empire' apples treated with preharvest inhibitors of ethylene perception and production with a delta absorbance (DA) meter

Harvest indices for apple fruits are usually based on destructive measurements such as the starch pattern index (SPI), firmness and internal ethylene concentration (IEC). One recent tool to estimate harvest windows is a DA meter, which provides a reading of difference in absorbance (I_AD). The I_AD estimates chlorophyll a (chl a) concentration based on absorbance differences between 670 and 720 nm. 'Empire' trees were either untreated or sprayed with Harvista (preharvest 1-methylcyclopropene; 1-MCP), or ReTain (aminoethoxyvinylglycine; AVG), modulators of ethylene perception and production, respectively. Fruits were harvested at three one-week intervals, and I_AD, IEC, firmness and SPIs measured. Correlations between individual fruits and harvest indices were weak, but when data were grouped and ranked by I_AD readings the relationships were stronger. However, preharvest treatments with ReTain, and especially Harvista, altered the relationships between I_AD and other harvest indices, especially IEC.