Stern, R.A., MIGAL, Galilee Technology Center, P.O. Box 831, Kiryat-Shmona 11016, Israel
Korchinsky, R., Department of Fruit-Tree Sciences, ARO, Volcani Center, Bet-Dagan 50250, Israel
Ben-Arie, R., Fruit Storage Research Laboratory, Kiryat-Shmona 10200, Israel
Cohen, Y., Department of Fruit-Tree Sciences, ARO, Volcani Center, Bet-Dagan 50250, Israel

'Cripp's Pink' apple often develops a poor colour at commercial harvest, resulting in economic loss. To determine if fruit colour could be improved without advancing ripening, 'Cripp's Pink' apple trees were sprayed with various synthetic auxins at different phenologic stages, from 30 d after bloom (30 DAB) until 150 DAB. The experiments were conducted in the North of Israel, from 2006 to 2008. Application of 50 mg I-1 of the synthetic auxin 2,4-dichlorophenoxypropionic acid (2,4-DP), as its butoxyethyl ester (Power™), or as its potassium salt 2,4-DP-P (Prigan™), at approx. 60 DAB, increased the rate of endogenous ethylene production by the fruit. This was accompanied by an increased concentration of anthocyanins in the fruit skin, and a higher percentage of red blush, without causing the fruit drop that is usually associated with increased levels of ethylene. Although both auxins accelerated fruit maturation, neither had any negative effects on fruit quality at harvest, or after 6 months of storage at 0°C. The effects were specific to 2,4-DP (and 2,4-DP-P). Several other synthetic auxins such as 2,4dichlorophenoxyacetic acid (2,4-D), naphthaleneacetic acid (NAA), 2,4-D plus NAA, and naphthaleneacetamide (NAD) plus NAA, had no effect on the red skin colour of 'Cripp's Pink' apple. 2,4-DP sprays therefore represent an effective treatment to improve the colour of 'Cripp's Pink' apple at commercial harvest, without adversely affecting other fruit quality attributes.