| Arceuthobium sichuanense is a perennial hemiparasite plant,which mainly distributes in Qinghai,Gansu,Sichuan province and Xizang Autonomous Region in Northwest China.In recent years,A.sichuanense has become one of the most serious diseases that affect the growth and propagation of natural spruce forests in Northwest China.In order to understand the genetic background and the cause of disease,and also to clarify furtherly the influence of different host and geographical selection pressure on the development of dwarf mistletoe,in this paper,ISSR(inter simple sequence repeat)molecular marker was used to analyze the genetic diversity and genetic structure of 100 A.sichuanense samples from 5 hosts in Qinghai,Gansu and Sichuan province.The results are as follows:(1)100 samples of A.sichuanense were amplified by 10 primers,and 130 bands were obtained with molecular weight between 190 and 2800bp.The number of bands amplified by different primers ranged from 8(UBC878)to 20(UBC807).The polymorphic bands were 129,and the proportion of polymorphism was 99.23%.The results show that there were abundant genetic variations within the population of A.sichuanense.Proportion of polymorphic bands ranged from 30.77%to 70.00%,and the orders from high to low is:Daocheng(SDC),Huzhu(QHZ),Luhuo(SLH),Zeku(QZK),Menyuan(QMY),Daofu(SDF),Dege(SDG).Luqu(GLQ),Xiahe(GXH)and Jianzha(QJZ).(2)Analysis of genetic diversity within and among the population was used to understand the differentiation of A.sichuanense at species level.100 samples which divided into ten groups were analysed by POPGENE software.The results showed that the trends between genetic diversity index and percentage of polymorphism were basically the same.The index of Nei's genetic diversity(He)and Shannon information index(I)were 0.3139 and 0.4765 respectively on species level.They were higher than the average value,and indicated that the genetic diversity of A.sichuanense was high.Genetic diversity whithin(HS)and among(Dst=Ht-Hs)the population were 0.1674 and 0.1582 respectively,which indicated that the genetic variation within the group(51.4%)was more abundant,while the gene flow(Nm=0.5287)between groups was relatively weak,which limited the gene communication among populations.The average genetic distance of ten populations of A.sichuanense was 0.2279,and the average genetic similarity was 0.799.Dege and Luqu with the maximum genetic distance(0.3605)and the minimum similarity(0.6974)showed that the differences between the two populations were large.Menyuan and Huzhu had the minimum genetic distance(0.0528)and the maximum similarity(0.9486)which showed that the genetic variation was small.(3)UPGMA cluster analysis of genetic distance showed that when the coefficient of genetic similarity was 0.56,100 samples could be divided into two groups:the samples from Qinghai and Gansu province were clustered into the first group,the samples from Sichuan were clustered into second group.When the similarity coefficient was 0.73,the first group was further subdivided into three subgroups:the samples from Menyuan(QMY)and Huzhu(QHZ)gathered for the first subgroup,samples from Jianzha(QMY)and Zeku(QHZ)were clustered into the second subgroup,the samples from Gansu were gathered into the third subgroup.When the genetic similarity coefficient was 0.59,the second group can be subdivided into two subgroups:the samples from Daofu(SDF)and Luhuo(SLH)can be divided into the first subgroup,Samples from Dege(SDG)and Daocheng(SDC)divided into the other subgroup.The results showed that the genetic diversity was abundant among different populations of A.sichuanense.(4)100 samples were divided into five groups according to different hosts:Picea crassifolia,P.wilsoni,P.purpurea,P.aspirate and P.likiangensis varˇbalfouriana.The genetic distance and similarity between groups were analyzed.The results show that the group of P.crassifolia and P.purpurea were the most similar(similarity=0.9768),while the difference was most significant between P.wilsoni and P.aspirate(genetic distance=0.2444).The genetic distance(0.1455-0.2444)among P.aspirate,P.likiangensis var balfouriana and other host groups were larger than 0.1.However,the genetic distance(0.0234-0.0703)among P.crassifolia.P.wilsoni and P.purpurea were less than 0.1.The result indicated the genetic differentiation was significant among the group of P.aspirate and P.likiangensis varˇ balfouriana.According to the cluster result among the host groups,A.sichuanense parasitized on Picea crassifolia,P.wilsoni,P.purpurea can be clustered into the first group.P.aspirate and P.likiangensis varˇ balfouriana with low genetic similarity were clustered into the second group.The result showed that there was obvious genetic differentiation among the hosts. |
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