EFFECT OF AUXIN INHIBITORS ON FRUIT GROWTH AND FRUIT SET OF ´MCINTOSH´, ´DELICIOUS´ AND ´GOLDEN DELICIOUS´ APPLES
It has been proposed that auxins are intimately involved in the process of fruit abscission in the postbloom period and they may play a central role in the promotion of abscission caused by chemical thinners on apples. A series of experiments were carried out to study the influence that auxin inhibitors may have on fruit set during the fruit development stage when chemical thinners are routinely applied. Three auxin transport inhibitors: 2,3,5-triiodobenzoic acid (TIBA), N-1-naphthphthalamic acid (NPA), 1-pyrenoylbenzoic acid (PBA), and an inhibitor of auxin action, α-(p-chlorophenoxy) isobutryic acid (PCIB) were selected. TIBA was incorporated into lanolin at concentrations of 200 and 500 mg.L-1 . When McIntosh fruit were approximately 10 mm in diameter spurs were selected that contained 2 fruit of the same size. Lanolin containing 200 mg.L-1 TIBA was applied to the pedicel of 0, 1 or 2 fruit per cluster. Fruit size was periodically measured. TIBA had no influence on either fruit growth or final fruit set. Another experiment was done on McIntosh where spurs were selected that contained just one fruit. TIBA at 0, 200, and 500 mg.L-1 in lanolin were applied to the pedicels of 15 fruit per tree. No treatment influenced fruit set at the end of the June drop. Lanolin paste containing 500 mg.L-1 NPA was prepared. A solution containing 500 mg.L-1 PCIB with 1% Regulaid surfactant was prepared. Forty spurs per tree containing 1 fruit were tagged on McIntosh and Golden Delicious when fruit size was 11 to14 mm in diameter. The pedicels on two sets of 10 spurs were treated with 300 mg.L-1 NPA. Fruit and leaves of one set of spurs were sprayed with 500 mg.L-1 and to another set that previously was treated with NPA. One set of spurs remained untreated and served as the control. Fruit growth was followed for 3 weeks and final fruit set was taken at the end of June drop. Spurs were tagged on Miller Sturdyspur Delicious when fruit size was approximately 10 mm in diameter, then lanolin containing 250 mg.L-1 TIBA, NPA or PBA was applied to sets of 10 spurs per tree. Two weeks after application all auxin transport inhibitors reduced final set significantly and comparably to about 40%, compared with that of the untreated control. No treatment influenced fruit growth or fruit set on McIntosh. The majority of fruit treated with NPA either alone or with PCIB slowed growth and ultimately abscised on the Golden Delicious trees. While auxin inhibitors clearly stimulated early abscission, the probable role of auxin was not clearly demonstrated in this investigation because no inhibitor caused abscission on McIntosh apples.
Greene, D.W. (2006). EFFECT OF AUXIN INHIBITORS ON FRUIT GROWTH AND FRUIT SET OF ´MCINTOSH´, ´DELICIOUS´ AND ´GOLDEN DELICIOUS´ APPLES. Acta Hortic. 727, 225-262
Malus × domestica, auxin transport inhibitors, 2,3,5-triiodobenzoic acid, TIBA, N-1-napthyphthalamic acid, NPA, α-(p-chlorophenoxy) isobutryic acid, PCIB, PBA, 1-pyrenolbenzoic acid, fruit drop