EFFECTS OF ENVIRONMENT ON FLORAL SEX RATIOS IN LYCHEE (LITCHI CHINENSIS SONN.)
High day/night temperatures (20/15°, 25/20° and 30/25°C vs. 15/10°C) after panicle emergence decreased the proportion of leafless panicles, increased the proportion of leafy panicles and reverted some reproductive buds to vegetative growth in the five lychee cvs Tai So, Bengal, Souey Tung, Kwai May Pink and Wai Chee. The reversion to vegetative characteristics at high temperatures was accompanied by a reduction in the proportion of female flowers. The relative order for the percentage of female flowers across all temperatures was 'Wai Chee'>'Bengal'>'Souey Tung'>Tai So'>'Kwai May Pink'. A cyclical leaf water stress (pre-dawn leaf water potential of -2.0 MPa vs. -0.6 MPa) after panicle emergence reduced panicle length and dry weight and induced flower drop in 'Kwai May Pink' lychee grown at 20/15°C. Water stress also eliminated female flowering (24.8% female flowers in control trees). It was concluded that temperature and water conditions after panicle emergence have strong effects on reproductive development and sex ratio in lychee. Localities which experience warm winters (daily maximum temperatures about 25°C) are best avoided for lychee culture. Lychee trees should be irrigated at full rates from panicle emergence to prevent moisture stress reducing fruit set.
Menzel, C.M. and Simpson, D.R. (1992). EFFECTS OF ENVIRONMENT ON FLORAL SEX RATIOS IN LYCHEE (LITCHI CHINENSIS SONN.). Acta Hortic. 321, 616-620