EFFECT OF 3,5,6-TRICHLORO-2-PYRIDYLOXYACETIC ACID ON CLEMENTINE EARLY FRUITLET DEVELOPMENT AND ON FRUIT SIZE AT MATURITY

The synthetic auxin 3,5,6-trichloro-2-pyridyloxyacetic acid increased fruit size of the clementine 'Fina' (Citrus reticulata Blanco) mandarin. When applied during the ''June drop'', increasing concentrations of 3,5,6-TPA increased fruit size, with a maximum response at 20 mg l(-1), but thinned up to 80% of fruits. However, an initial depressive effect on fruit growth was observed due to treatment. When sprays were applied after the June drop, fruit size was improved, but diameter increment was significantly greater only for 20 mg l(-1). However, fruit thinning was much less, with a maximum of 40% for 25 mg l(-1), equivalent to the thinning obtained with 10 mg l(-1) applied during the June drop. No depressive effect of treatment on fruit growth occurred. Our results indicate that final fruit size is only partially related to fruit competition; only when fruit thinning was very heavy (higher than 40%) did it affect fruit size. Treated fruit accumulated significantly greater amounts of dry matter in the juice sacs as a result of increased fruit sink strength. Fruit peel, pulp, juice and acid contents were not affected by treatment on a relative value but were significantly increased in absolute terms.