Temperature model of litchi flowering—From induction to anthesis

To study the effect of air temperature on the physiological stages of flowering in litchi (Litchi chinensis Sonn.), we pruned the two apical buds of ‘Yu Her Pau’ litchi to release the axillary buds into inflorescence induction. We used three years of flowering performance data, including 14 pruning episodes, along with temperature data from the field, to develop three different growth models: an “inflorescence induction model” (IIM), a “floret anthesis model” (FAM), and an “inflorescence length model” (ILM). Using the regression relationship between assumed temperature and the coefficient of variation in “chilling-degree-hours” (CDHs), and the “thermal-degree-hours” (TDHs) of all treatments, we estimated the base temperatures of inflorescence induction and floret anthesis to be 23.42 °C and 19.32 °C, respectively. Furthermore, using the IIM, we divided inflorescence induction into “pre-induction” and “induction” phases, and these had chilling requirements of 4030 and 3343 CDHs, respectively. Florets entered anthesis when they reached 2397 TDHs after inflorescence emergence. The length of the inflorescence flush can be deduced from the CDHs between inflorescence emergence and floret flowering, and the ILM indicated that the length of the inflorescence flush was positively correlated with the CDHs during this period. However, the FAM showed that the timing of anthesis was positively correlated with the speed of thermal temperature accumulation. This finding indicates that the process from inflorescence emergence to floret anthesis results from a competition between the chilling requirement for inflorescence flush elongation and the thermal requirement for floret anthesis.