Aminoethoxyvinylglycine, Naphthalene Acetic Acid and Ethephon: Impacts on Pre-harvest Fruit Drop, Volatile Compounds Profile, and Overall Quality of ‘Galaxy’ Apples

The objective was to evaluate the effect of isolated or combined growth regulator application on pre-harvest fruit drop, physicochemical quality, and the volatile organic compound (VOC) profile of ‘Galaxy’ apples after harvest plus 7 days of shelf life at 20 °C. The treatments evaluated were: (1) control (water application); (2) naphthalene acetic acid (NAA); (3) aminoethoxyvinylglycine (AVG); (4) 2-chloroethylphosphonic acid (ethephon); (5) AVG + NAA; (6) AVG + ethephon; (7) NAA + ethephon and (8) AVG + NAA + ethephon. Pre-harvest application of AVG and AVG + NAA resulted in lower fruit drop, decreased the internal ethylene concentration, ethylene production, respiration rate, and internal space, and also maintained higher acidity and flesh firmness. In addition, AVG and AVG + NAA retarded ripening and suppressed some important VOCs, including characteristic alcohols and esters of ‘Galaxy’ apple 7 days after harvest. AVG alone or combined with other growth regulators did not negatively affect the development of the red skin color. Application of NAA alone or combined with ethephon, despite increasing the concentration of important esters, reduced fruit quality and increased ripening. This happened due to the fact that these growth regulators promoted higher internal ethylene concentration, ethylene production, and respiration rate, which accelerated flesh firmness loss.