S16 - Session P1 - Impact of preharvest plant growth regulators and reflective groundcovers on Honeycrisp skin coloration and fruit maturity

Authors: Tekan Rana, Macarena Farcuh *

Marketability of the high value apple cultivar Honeycrisp is strongly associated to red skin coloration. Hot and humid weather and lack of uniform light distribution throughout the canopy hamper red color development. Reflective groundcovers have shown to enhance the tree light environment. Fruit maturity can also influence apple surface blush. Plant growth regulators, such as aminoethoxyvinylglycine (AVG, ReTain®), which inhibits ethylene production, are used to decrease fruit drop and manage harvest windows, but delay fruit maturity, thus potentially impacting red skin coloration. Our aim was to characterize and compare the effects and interactions of reflective groundcover (Extenday) and AVG treatments in red skin and background color, blush surface percentage, ethylene production rates, and fruit drop of Honeycrisp fruits from the lower third of the canopy. Four treatments were established: T1, AVG+ Extenday; T2: NoAVG+ Extenday; T3: AVG +NoExtenday; T4: NoAVG+ NoExtenday. AVG (333 g/acre) was applied and reflective groundcovers were deployed four weeks before anticipated harvest. Honeycrisp fruit were harvested at 0, 1 and 2 weeks after anticipated harvest, and evaluation of the traits listed above were conducted on each date. Our results showed that the lowest hue values for surface and background color at all dates were for T2, followed by T1 and T4, while T3 fruit were highest, indicating that Extenday deployment increased red skin coloration and background color change from green to yellow even in AVG-treated fruit. Differences in red skin coloration correlated with blush surface percentage results. Ethylene production was highest in T2, followed by T4 and T1, and lowest in T3 fruit, indicating that Extenday can affect fruit ethylene production rates, thus fruit maturity, independent of AVG treatment. Extenday treatment did not enhance fruit drop. Our results contribute to further understanding how preharvest tools can influence Honeycrisp fruit ripening and quality.