The advancement of research on litchi and longan germplasm resources in China

Litchi and longan are famous southern subtropical fruits in China. Besides closely related to each other taxonomically, litchi and longan share many similarities in origin, cultivation history and environmental requirements; furthermore, the developments of research on litchi and longan germplasm resources are somewhat similar and comparable. This paper reviews the literature on origin and distribution, collection and conservation, classification and identification, selection and breeding of litchi and longan germplasm resources in China. The classification of litchi and longan can be divided into three stages: classification based on morphological traits, classification by isozyme analysis and DNA markers. The expression of morphological traits is often affected by environmental conditions; the number of loci that isozyme analysis can examine is small, cultivars, which are closely related often have identical isozyme patterns. The limitations of classification based on morphological traits and isozyme analysis are then overcome by the utilization of molecular markers. At present, most new litchi and longan cultivars are selected from superior seedlings obtained after open-pollination or sport; germplasm with desirable characteristics such as aborted seeds, rather big-fruit and rather late-bearing have not been fully exploited. In order to achieve the goal of improving fruit quality and agronomic characteristics, it is suggested that additional studies of genetic diversity on litchi and longan germplasm should be carried out with more powerful markers such as SSR and ISSR; marker assisted selection (MAS) should be employed to improve litchi and longan's cross breeding efficiency.