Interaction of temperature and vegetative flush maturity influences shoot structure and development of lychee (Litchi chinensis Sonn.)

Potted lychee trees (cv. Tai so) of varying vegetative flush maturity were grown under a range of temperature regimes and monitored for subsequent shoot structure and development. A combination of low temperature (15/17 or 18/13 °C day/night) and high vegetative flush maturity was necessary for floral initiation to occur. Exposure to high temperatures (28/23 °C) invariably resulted in the production of vegetative shoots, irrespective of flush maturity. Strong floral initiation was marked by the emergence of terminal panicles and accompanying axillary panicles. A decrease in vegetative flush maturity or increase in temperature (e.g. 23/18 °C) resulted in a decrease in axillary shoot formation and the production of several intermediate shoot structures. These included leafy panicles, stunted panicles, partially emerged buds and non-emergent swollen buds, often produced on the same tree. At 23/18 °C, closer synchronisation of initial flush maturity was required for the production of a consistent shoot-type. Trees with synchronised mature flushes (I-2) at 23/18 °C resulted in the production of swollen terminal buds. Healthy trees were maintained in this state for at least 11 months. These results indicate that both temperature and flush maturity can influence subsequent shoot structure of lychee. In the absence of either a strong floral temperature (18/13 °C) or strong vegetative temperature (28/23 °C), slight differences in initial flush maturity have greater impact on the type of emerging shoot formed.