Studies on the Reduction of Seed Number in Mandarins1

Abstract

Abstract Studies of pollen germination, stigmatic treatments and a field experiment were conducted in an attempt to decrease seed number of mandarin-type fruits (Citrus reticulata Blanco cv. Dancy and C. reticulata Blanco cv. Temple). Gibberellin (GA3) in the medium inhibited germination only above 250 ppm; cycloheximide inhibited it at 0.1 ppm. Treatments of the above and other compounds applied to stigmatic surfaces decreased either set or yield. Field treatments with 20 ppm GA at early- or mid-bloom or 150 ppm naphthaleneacetic acid (NAA) applied when fruitlets were 5 or 10 mm in diameter alone or in combinations, decreased seed number to 72% for ‘Dancy’ and 82% for ‘Temple’. Effects of NAA were greater than for GA. Neither treatment caused thinning. Instead, fruit number and yields increased, while fruit size decreased slightly. Bioassays of NAA-treated fruitlets showed residual active NAA 25 days after spraying as well as an increase in native gibberellin-like activity which was highest in NAA + GA-treated fruitlets.