IAD Values in Relation to Internal Ethylene Concentrations in `Delicious' Apple Fruit Harvested from Trees Treated with Retain and Harvista

The DA meter provides a nondestructive measurement of chlorophyll in fruit skin using visible/Near Infra Red spectroscopy (vis/NIR) values expressed as the Absorbance Difference index (I_AD).  Internal ethylene concentrations (IECs) remain the standard for measurement of apple fruit maturity and our studies and that of others show good relationships between IEC and I_AD values at harvest, suggesting that the DA meter may be useful for assessing harvest maturity. However, many apple industries use the plant growth regulators (PGRs) Harvista (1-methylcyclopropene; 1-MCP) and ReTain (aminoethoxyvinylglycine; AVG), inhibitors of ethylene production and perception, respectively, to reduce fruit drop and manage the harvest. The effects of these PGRs on the relationship between IEC and I_AD values were studied.  Fruit were harvested from `Delicious’ trees either untreated or treated with Harvista or ReTain and separated into eight I_AD value categories in 0.2 unit intervals from 0.2 to 1.8.  In untreated fruit, IECs were higher when fruit were more mature (lower I_AD values).  There were, however, negligible increases in IEC for Harvista and ReTain treated fruit, regardless of maturity.  Therefore, DA meter readings in fruit treated with PGRs are not good indicators of harvest maturity. Correlations between IEC, α-farnesene, conjugated trienols (CTols) and superficial scald in cold storage were also investigated.