| The inflorescence of litchi is composed of both panicle (compound raceme) and dichasia. The function
of component panicle is to build up the skeleton of the inflorescence, and the component dichasia is special for the
differentiation of flowers. The litchi inflorescence can be regarded as“cymes based on panicle”. There are two turning
points in the floral formation processes of litchi. First, the physiological differentiation is switched into the morphological
differentiation at the terminal buds of last autumn shoots. Second, the developing inflorescence transforms its differentiating
status from panicle development to cymose differentiation. Therefore, the entire floral formation process can be divided,
by using the two turning points, into three stages as follows: (1) Floral primordial induction and development. (2) Panicle
emerges and elongates and the building up of the skeleton of the inflorescence. (3) Setting of flowers on cymose branches
and the differentiation of floral organs. In this paper, we discussed how the important internal and external factors, such as
nutritional status of trees, temperature, rainfall, sunlight affect and restrict the floral formation processes of litchi. It was
pointed out that too heavy cropping which depleted the nutrients inside the tree is the main internal reason affecting floral
formation of next year, and how the cold waves invaded in winter and spring is the most important environmental factor
restricting the floral formation process of litchi. It was thought that litchis in Southern China need cold waves invade at right moment and right strength during the period of winter and spring for their floral formation, and the improper coming of the cold
waves in winter and spring is the important external reason to cause the “irregular bearing” of litchi. We also emphasized, that
both adequate internal nutrients and suitable weather conditions are necessary for the floral formation of litchi. Thus to regulate
the physiological status of litchi trees is the main way to promote floral formation and flower retention while the environmental
conditions are undesirable. |
