INFLUENCE OF GIBBERELLIC-ACID ON EARLY FRUIT-DEVELOPMENT, DIFFUSIBLE GROWTH-SUBSTANCES AND CONTENT OF MACRONUTRIENTS IN SEEDLESS CLEMENTINE MANDARIN

The influence of the application of GA3 (100 mg/l) to individual leafy inflorescences of Citrus reticulata Blanco cultivar 'Fino' on fruit development, diffusible growth substances and content of macronutrients was studied. GA3, applied during stylar abscission, reduced the percentage of fruit abscission during the June drop of fruits and was associated with an early fruit size increase. Therefore, fruits which would normally abscise because of their relatively small diameter, set and developed until maturity. The content of GA-like substances attained a maximum on Day 4 after treatment and was practically zero from Day 9. A diffusible auxin-like compound of unknown nature, which was not present in untreated fruits, was found in fruits treated with GA3, with maximum activity on Day 2. Within 5-16 days after application of GA3, the total content of nitrogen, phosphorus and potassium in leaves from inflorescences treated with GA3 decreased and the content in fruits increased relative to untreated inflorescences. It is suggested that the increase of fruit-set after GA3 application is due to an increased availability of nutrients from the leaves, although whether this effect is carried out by GA3 or by GA3-induced auxins cannot be decided. © 1979.