Effects of 1-aminocyclopropane carboxylic acid on the rate of ethylene release from detached fruiting spurs and on fruit abscission in apple

Summary1-Aminocyclopropane carboxylic acid (ACC) was applied to apple (Malus × domestica Borkh.) trees or to individual fruiting spurs between full bloom (FB) and 31 d after full bloom (DAFB; mean fruit diameter of 20 mm) to determine the effects of ACC on the ethylene released from detached spurs and on fruit abscission. The rate of ethylene release from detached fruiting spurs increased 1 d after applying 50 mg l–1 ACC at full bloom or 16 DAFB (mean fruit diameter of 10 mm), but ACC had a reduced effect on the rate of ethylene release when it was applied 31 DAFB (mean fruit diameter of 20 mm). ACC reduced fruit set in ‘GoldRush’ apple in a concentration-dependent manner in 2009 and in 2010, but had no thinning activity on ‘Pink Lady’ in 2010. ACC at 200 mg l–1 resulted in the yellowing and abscission of ‘GoldRush’ spur leaves in 2009, but not in 2010. The effects of combining ACC and 5 mg l–1 naphthaleneacetic acid on fruit set in ‘GoldRush’ apple were additive. The application of 200 mg l–1 ACC when fruit are ca. 10 mm in diameter may therefore be a useful chemical thinning treatment for apple fruit.