Endogenous ethylene production and fruit quality in peaches in response to ethephon and ACC as chemical thinners

Hand thinning of flower and/or fruitlets are usual practices to regulate fruit crop load in peach (Prunus persica L. Batsch) trees to ensure fruit size and quality, but they are labour-intensive and expensive. Ethylene plays a key role in flower and fruit abscission, hence the use of plant growth regulators related to this natural plant hormone can be a useful tool to regulate fruit crop in peach trees. The purpose of this study was to evaluate the efficacy of the ethylene precursors ethephon (2-chloroethylphosphonic acid) and ACC (1-aminocyclopropane-1-carboxylic acid) as chemical thinners on ‘Flatbeauti’ peach cultivar. For two years, foliar applications of ethephon (150 ppm) and ACC (500 ppm) were tested at full bloom and when the average fruitlet diameter was around 20 mm. Thinning efficacy and fruit maturity parameters were related to the ethylene evolution pattern throughout peach fruit growth. As a mean of two years, ethephon and ACC reduced fruit crop load in a 30-40%. Both treatments triggered an ethylene pick around 2-4 days after applications, however, ACC produced higher ethylene picks than ethephon. Both treatments at 20 mm of ethephon and ACC increased ethylene endogenous production up to harvest and this positively influenced the fruit colour (higher red colour coverage). No significant differences were observed for fruit firmness and sugar content.