Flower Sex Expression in Lychee (Litchi chinensisSonn.) Is Affected by Gibberellic Acid and Naphthalene Acetic Acid

Abstract

ABSTRACT Gibberellic acid (GA3) at 25, 50, and 100 mg-L−1 and naphthalene acetic acid (NAA) at 20, 40, and 80 mg-L−1 were sprayed to runoff on flower panicles of 15-year-old lychee trees one week after panicle emergence. Trees sprayed with water only were used as the control. The number of male flowers was increased quadratically by NAA compared to the control in 2000, and 2001. The number of hermaphrodite flowers functioning as female (HF-F) and the number of hermaphrodite flowers functioning as male (HF-M) was reduced quadratically by all concentrations of NAA both years. The greater the NAA concentration, the greater the reduction. The total number of flowers was also reduced by all NAA concentrations both years. Fruit set (percentage of total HF-F flowers) was reduced quadratically by NAA in 2001, but had no effect in 2000. The number of male flowers was increased quadratically by GA3 both years. Regression analysis also showed a positive relationship between GA3 and HF-F flowers both years. However, hermaphrodite flowers functioning as male (HF-M) was reduced quadratically by GA3 both years. In addition, the total number of flowers and fruit set was increased quadratically by GA3 both years. GA3promotion of male flowers, HF-F production, and increased fruit set may have important bearing on yield improvement.