| Gnetum parvifolium(Warb.) C.Y.Cheng ex Chun,a rare and endangered species of Gnetum,has been listed in China Species Red List.This species distribute in Fujian, Guangdong,Guangxi,Yunnan,Guizhou,Hainan,Hunan and Jiangxi in China,also in Laos and Vietnam.To investigate the mechanism of endangering and to make corresponding steps for population restoration,we studied the genetic diversity and genetic structure of 11 populations of Gnetum parvifolium in Fujian,based on ISSR molecular marker and morphological marker.The results are as follows:ISSR molecular marker shows that G parvifolium exhibits comparatively high genetic diversity at species level while comparatively low at population level.211 samples from 11 populations were examined by 13 ISSR primers.131 loci and 115 polymorphic loci were gained.At species level,the genetic diversity(PPB=87.79%, H=0.2202,SI=0.3412,Hs=0.2460) is at a high level among gymnosperms.At population level,the diversity(PPB=48.02%,H=0.1719,SI=0.2558,Hs=0.201) is lower than the average level of that of other gymnosperms,long-lived perennial plants and outcrossing plants respectively.Such genetic diversity and genetic structure style of G parvifolium indicates that this species has a strong potential for survival, adaptation and expansion,but its population genetic diversity has been effected by habitat fragmentation and human activities.ISSR molecular marker also shows that most of the variation of G parvifolium was found within populations.The genetic differentiation is mainly caused by selection pressure and gene flow rather than genetic drift.Four different indexes(coefficient of gene differentiation Gst population differentiation value calculated by Shannon's information index,φst by AMOVA,and population divergence valueθB) were used to measure the genetic structure and got a consistent result,showing that about 20% genetic variation was attributed to among populations and the rest within populations. The gene flows deduced fromθB and Gst are 0.8453 and 1.3629,respectively, indicating that gene flow plays a more important role than genetic drift in the maintenance of population genetic structure.UPGMA cluster analysis and Mantel test show that there is a moderate positive correlation(r1=0.4184,P1=0.0063＜0.05; r2=0.5273,P2=0.0010) between genetic distance and geographic distance of G. parvifolium populations,and that the population genetic differentiation conforms to isolation-by-distance pattern,suggesting that gene flow and natural selection are major factors in the maintenance of such a population genetic structure,and that the effect of genetic drift is not obvious.In morphological marker study,we measured 15 characters of G parvifolium from 11 populations,including 1139 leaves from 116 samples.The diversity index is 1.9281 at species level and 1.7573 at population level.91.14%of all genetic variation distributes within populations.UPGMA cluster analysis and Mantel test also support that there is a positive correlation(r=0.6216,P=0.0020＜0.005) between genetic distance and geographic distance.In a word,the result of morphological marker analysis are in agreement with that of molecular ones.Human activities and habitat destruction contribute to the population degradation of G parvifolium,but this degradation has little detectable effect on the genetic structure of the target species due to limited impactive time.To protect and recover G parvifolium populations in Fujian,we propose to rely mainly on in situ conservation,supplemented by ex situ conservation,giving key protection efforts to Yongtai(YT),Yongchun(YC),Longyan(LYS) and Luoyuan(LYX) populations due to their higher level genetic diversity,and giving key recovery efforts to Fuzhou(FZ),Sanming(SM) and Pinghe(PH) ones due to lower level diversity.
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