Temperatures above 20°C reduce flowering in lychee (Litchi chinensis Sonn.)

Abstract

Flowering in lychee (Litchi chinesis Sonn.) is promoted by low temperatures, but the critical level and duration of chilling required for successful induction are not known. The effects of maxima/minima of 15°/5°, 20°/5°, 20°/10°, 20°/15°, 25°/10°, 25°/15°, 25°/20° or 30°/20°C on vegetative growth and flowering of cvs Kwai May Pink and Casino were investigated. In a second experiment, plants of cv. Wai Chee were given 0, 2, 4, 6, 8,10 or 31 weeks of induction at 15°C before transfer to non-inductive conditions at 30°/20°C. In a third experiment, cv. Wai Chee was grown at 15°C and given 0, 1, 2 or 8 h above 20°C (0, 2, 4 or 15 h above 15°C) per 24 h. In Experiment 1 with cv. Kwai May Pink, there was vegetative growth at 25°/20°C and 30°/20°C, a mixture of vegetative growth and flowering at 25°/10° and 25°/15°C, and flowering at lower temperatures. Cv. Casino responded similarly, except that there was no growth or flowering at 25°/10°C and 25°/ 15°C. For both cultivars, nearly all branches flowered at 20°/15°C or lower. Flowering in ‘Wai Chee’ occurred with four weeks at 15°C before transfer to warmer temperatures and was greatest with six weeks. There was also an effect of treatment on the type of inflorescence, with fewer leaves after ten weeks of induction. Plants of ‘Wai Chee’ exposed to 2 h above 20°C per day were mainly floral, whereas those given eight or more hours were vegetative. It was concluded that flowering in lychee was best after ten weeks at 15°C, while periods of 8 h or more per 24 h above 20°C were detrimental.