四川西部濒危植物桃儿七遗传多样性的RAPD分析

Abstract

Sinopodophyllum hexandrum( Royle) Ying is an important medicinal and endangered species. Recently,the size of the wild population of S. hexandrum in western Sichuan Province has been noted to be very low and declining rapidly.Analysis of random amplified polymorphic DNA( RAPD) markers was conducted on seven natural populations of S.hexandrum in western Sichuan Province in order to investigate the genetic diversity and genetic structure of the populations.Leaf samples of 140 individuals from the seven populations were collected. Twelve RAPD primers were designed to generate highly reproducible and stable DNA fragments( the sizes of DNA bands ranged from 200 to 1500 bps). One hundred and eleven discernible DNA fragments were produced depending on these primers,and 32 fragments were polymorphic loci( mean 9.3 bands and 2.7 polymorphic bands per primer). The percentage of polymorphic bands( PPB) was 28.83% at the species level,and PPB within population ranged from 4. 50% to 16. 22% with an average of 10. 30%. The result of POPGENE analysis indicated that the level of genetic variation of S. hexandrum( He = 0.0622,Ho = 0.0987) was lower than other endangered plants. At the species level,the average effective number of alleles per locus( Ae) was 1. 1011. The average expected heterozygosity was estimated to be 0.0193 within populations( He) and 0.0622 at the species level( Ht).Shannon's index( Ho) ranged from 0.0110 to 0.0587,with an average of 0.0269 at the population level( Hpop) and 0.0987 at the species level( Hsp). Among the seven populations investigated further,the MNG population revealed higher variability( PPB,16.22%; Ae,1.0569; He,0.0362; Ho,0.0587),whereas the MSG population had the lowest variability( PPB,4.50%; Ae,1.0105; He,0.0065; Ho,0.0110). As revealed by the AMOVA analysis,a high level of genetic differentiation among populations was detected,68. 74% of the genetic differentiation occurred between populations and 31. 26% within populations. Gene flow( Nm = 0.4429) was low between natural populations of S. hexandrum in the area.Nei' s genetic identity( I) values varied from 0.9189 to 0.9883 between the pairs of populations; Populations DXB and YLG had the lowest( 0. 9189),whereas MNG and LHK had the highest( 0. 9883). The dendrogram was constructed by the UPGMA method using Nei's genetic distance values based on RAPD. Two clusters were defined among seven populations,no significant correlation was found between geographic distribution and the genetic distance on the UPGMA tree. The correlation coefficient( r = 0.3747; P = 0. 0350) by Mantel test did not show any significant relationship between the matrices of geographical distances and pair- wise genetic distances based on RAPD. Species breeding system and limited gene flow among populations were plausible reasons for the high genetic differentiation observed in this species. On the basis of the genetic and ecological information,some appropriate strategies for conserving the endangered medicinal species in this region were proposed: namely,keeping a stable environment suitable for the breeding and growth of population,rescuing and conserving the core populations( such as MNG in Songpan County) for in situ conservation and also trying to protect all of the existing populations.