Studies On Classification And Genetic Diversity Of Cycas Segmentifida Complex In Baise Of Guangxi, China

Cycas segmentifida complex is composed of eight formerly described speicies which share similar morphology and affinity. It includes C. segmentifida, C. longiconifera, C. multifida, C. crassipes, C. acuminatissima, C. xilingensis, C. longlinensis and C. guizhouensis. The present study charified the interspecific relationships, genetic diversity and its partitioning into Cycas segmentifida complex members on morphology and molecular biology, and the strategy for conservation was proposed.Based on the results of morphological observation and ISSR marker analysis, C. acuminatissima, C. longiconifera, C. multifida, C. xilingensis, C. crassipes should be sunk into C. segmentifida. C. longlinensis is should be treated as a synonym of C. guizhouensis. That is to say, there are two recognized speicies (C. segmentifida and C. guizhouensis) in the Cycas segmentifida complex. According to the present study and relevant data available, we concluded that there are six cycad speicies (Cycas segmentifida, C. guizhouensis, C. miquelii, C. ferruginea, C. bifida, C. debaoensis ) in Baise district of Guangxi province.Genetic diversity as detected by ISSR marker analysis was very low with the porportion of polymorphic bands (PPB) ranging from 14. 75-36. 07% and mean expected heterozygosity (H_e) 0. 0974 at the population level in the complex. However, the genetic differentiation (G_GT=0. 6507) between populations was unexpected high. Theeffect of small population (such as genetic drift or inbreeding) due to many factors were postulated to be one of the main reasons for low intra-population genetic diversity and high inter-population genetic differentiation. It is assumed that the complex was once distribed more widely than it is today. It was possible that the extensive gene flow had happened in the past, these would have led to moderate or slightly high genetic diversity at the species level of Cycas segmentifida (He= 0.2067) and Cycas guizhouensis (Ne=0. 1799) .According to the extant distribution characteristics and genetic structure in Cycas segmentifida complex, the priority should be to protect all the existing populations in situ conservation and prevent anthropogenic destruction, allowing them to propagate and increase in size through natural regeneration. Especially, those populations with larger area, more individuals and higher genetic diversity should be paid more attention. At the meantime, the program of ex situ conservation was suggested in the populations with less individuals and lower genetic variation, and most of the populations should be sampled in order to retain as much genetic diversity as possible.