Abstract: The commercial production of litchi (Litchi chinensis Sonn.), a subtropical evergreen fruit tree, has been restricted in the two narrow areas of 17o-32o latitude in the north and south hemispheres. Within the multiple cultivars-based industrial structures, unreliable flowering has taken place in almost all litchi cultivars. The flowering status of varieties, flower bud differentiation stage performance, influence factors, flower bud differentiation mechanism and flowering regulation are reviewed in this paper. It is considered that, litchi trees must have fully matured terminal shoots in autumn and be florally induced under chill conditions for a quite long period during the winter. Primordial inflorescence initiated upon the ascending temperatures and with release of water stresses during late winter or early spring, the inflorescence and flowers developed at mild conditions with warm days and cool nights. Any one unsatisfactory factor during the phase changes might cause failure of flower formation. The major factors influencing litchi floral development are state of terminal shoots, temperatures and water. Carbohydrate accumulation in shoots and the endogenous hormones affect flowering. In order to solve the instability problem in production of flowering and ensure good flowering under extreme and marginal conditions, the molecular mechanism about litchi floral differentiation and why young shoots and leaves could not be florally induced with chills, how the chill signals perceived and transduced, stimulate the floral transition of the terminal buds, when and how the flower sex is determined should be studied, and to explore nutrient, water management, growth regulators and other mechanical measures according to the phase changes of floral differentiation.

Key words: litchi (Litchi chinensis Sonn.) , floral induction , floral initiation and development , phase change , shoot state , temperature , water