Induction of Parthenocarpic Growth of Apple Fruits with Gibberellins A₃and A₄

The effects of gibberellins A3 and A4, butylcellosolve ester of GA3, 2-chloro, 4-fluorophenoxyacetic acid, and 1-naphthyl N-methylcarbamate on the induction of fruit growth, in the absence of pollination and fertilization, were determined in several cultivars of Malus sylvestris Mill. Gibberellins A3 and A4 (5 x 10-3 and 5 x 10-2 M) induced parthenocarpy (Sops-of-Wine) and sustained fruit development to maturity. Gibberellin A4 was more effective than GA3. Butylcellosolve ester of GA3 caused initial fruit enlargement, but all fruits abscised before 55 days after treatment. 2-Chloro, 4-fluorophenoxyacetic acid caused the treated flowers to persist but failed to induce fruit growth; 1-naphthyl N-methylcarbamate was inactive. 2. Using gibberellin A4 (5 x 10-3 M) as a parthenocarpic stimulus, fruit growth was readily induced in cultivars of Sops-of-Wine and Wealthy, with growth rates, final size, color, and general quality comparable to seeded fruits. Parthenocarpic Delicious were smaller at maturity than seeded fruits. Initial fruit growth was induced in Jonathan and Rhode Island Greening, but all parthenocarpic fruits of these cultivars abscised before reaching maturity. 3. Inspection of mature parthenocarpic Sops-of-Wine and Wealthy fruits as compared to seeded ones of the respective cultivars revealed (a) an equal or larger polar diameter and a smaller transverse diameter, (b) a thicker cortex in the apical region, (c) smaller locular cavities, and (d) a smaller core diameter.