Genetic diversity of allozymes in populations of Cycas panzhihuaensis L. Zhou S.Y. Yang

摘要

Panzhihua cycad, Cycas panzhihuaensis, is restricted to S.-W. Sichuan and N.-W. Yunnan, China, in dry-hot valleys of Jinsha River and its tributaries. The populations of wild cycad forests in Panzhihua district have been preserved much better than natural cycads in other places of the China. In Panzhihua district, the specimens from Limestone Mt and Jinjia Cun have been identified as Cycas panzhihuaensis and those from Baguan River as Cycas baguanheensis. Thirteen enzyme systems, including AAT, DIA, GDH, IDH, LAP, G6PD, MDH, ME, PGD, PGM, SKD, SOD and TPI were assayed. Twenty-eight loci were resolved and of them, 23 loci were found to be monomorphic and 5 to be polymorphic in all material examined. Based on statistic analysis of data from enzyme electrophoresis, genetic variability measures at all of the loci in 3 populations were obtained. The measures showed that genetic diversity in natural populations of Panzhihua cycad is much lower than those of all the other Gymnosperms and Angiosperms. F-statistics at all polymorphic lici were summarize,d which indicate that the ratios of heterozygotes are very low at these lici (i.e. homozygote excess) and about 14% of genetic variation occurred among populations and nearly 86% of genetic variation within populations. Nei's coefficients of unbiased genetic identity and genetic distance showed that similarity between populations is very high and genetic distance is very low. Using Nei's coefficient, 3 populations were clustered by UPGMA. Using Prevositi distance coefficient, the Wagner tree was produced by rooting at midpoint of longest path. The above results from analysis of genetic identify and genetic distance do not support the idea that 3 populations of Panzhihua cycads are divided into two species.