EFFECT OF THE SYNTHETIC AUXIN 3,5,6-TPA ON PRE-HARVEST DROP, FRUIT QUALITY AND MATURATION OF 'DELICIOUS' AND 'JONATHAN' APPLES

The main apple cultivar grown in Israel, ‘Delicious’, and a minor cultivar, ‘Jonathan’, are prone to massive pre-harvest drop. Spraying both cultivars with the synthetic auxin 3,5,6-trichloro-2-pyridyl-oxyacetic acid (3,5,6-TPA) reduced pre-harvest fruit drop and increased yield. Application of 40 mg L^-1 3,5,6-TPA, two weeks before anticipated harvest (WBH) or 30 mg L^-1 3,5,6-TPA at four and two WBH showed the best results, and were as effective as 2,4,5-TP, which was the commercial product commonly in use until withdrawn. There were no negative effects on fruit quality at harvest or during 9 months’ storage. Therefore, 3,5,6-TPA can be recom¬mended for routine use on ‘Delicious’ and ‘Jonathan’ apples.