Study Of Genetic Variability On Haloxylon Ammodendron

Haloxylon ammodendron(C.A.Mey.) Bunge,which belongs to the genus Haloxylon Bunge in the family Chenopodiaceae,is Perennial small trees,sometimes shrubby.As dominant desert paint,H.ammodendron played an important role in the maintenance of the structure and function of the whole ecosystem,the preventability of land desertification and the improvement of the desert climate.During the last few decades,natural factors and overall land reclamation and cultivation,over-grazing and over-cutting and digging had resulted in the destruction and recession of H. ammodendron and development of mobile sand dunes.H.ammodendron urgently need rehabilitation and development.Moreover,Cistanche deserticola Y.C.Ma is a parasite on the roots of H.ammodendron.Cistanche(Cistanche deserticola) is domestic and foreign well-known Chinese herbal medicine,known as "desert ginsing" for a very high economic value and development prospects.However,the genetic differences between parasitized and nonparasitized H.ammodendron were largely unknown.In this paper,inter-simple sequence repeat(ISSR) molecular markers were used to study genetic structure and genetic variability of H. ammodendron,to explore the endangered mechanism of H.ammodendron and to predict the genetic potential of H.ammodendron populations.At the same time,by comparing the space mutation with the control of H.ammodendron on the genetic differences,we aimed to provide a scientific basis for the selection of superior varieties of H.ammodendron.Firstly,genetic diversity levels were assessed based on 146 individuals of 8 natural populations from Inner Mongolia,Qinghai,Ningxia and Gansu provinces using ISSR molecular markers.Nine selected primers produced a total of 135 discernible bands,of which 127(94.07%) were polymorphism.The Nei's gene diversity(h) and Shannon's information index(1) were 0.2390 and 0.3761 respectively at the species level,which meant that there existed a relative high genetic diversity within the H.ammodendron population.The genetic diversity of YA population of Inner Mongolia was highest(h = 0.2341,I = 0.3477),and the genetic diversity of GS population of Qinghai was lowest(h = 0.0479,I = 0.0698) at the population level.At the regional level,both the h and I value,0.2615 and 0.3975,of populations from Inner Mongolia were the highest among four regions.The gene flow(Nm) was 0.715 at the population level.The level of gene flow of H.ammodendron was between the self plants and wind-pollinated outcrossing plants,which meant that H.ammodendron was likely to adopt self-pollination and outcrossing breed system.AMOVA analysis indicated that genetic variation of H.ammodendron is much higher among populations(56.86%) than within populations(43.14%).A cluster analysis(UPGMA) was used to generate dendrogram based on Nei's genetic distances among 8 populations.The results showed that three populations from Inner Mongolia(YA,DL and JT) were clustered as the first clade,and three populations from Qinghai(GH,GS and XJ) were clustered as the second clade and two populations from Gansu and Ningxia(MQ and YC) were clustered as the third clade which showed the closer genetic relationship between them.Secondly,the inter-simple sequence repeat(ISSR) marker was used to assess the genetic variations and relationships among 6 accessions of H.ammodendron with a total of 120 individuals collected from three localities in the Alxa Desert,Inner Mongolia,China.At each locality,individuals both parasitized(PP) by C.deserticola and nonparasitized(NP) were sampled.The results showed that Nei's gene diversity and Shannon's index of PP accessions were higher,but were not significantly different,from those of NP accessions.A UPGMA dendrogram showed that genetic differentiation existed between PP and NP accessions,which may be attributed to low gene flow between the NP and PP groups(Nm＜1).Meanwhile,the relationship between genetic distance and geographic distance within each group,although not statistically significant in this study,may be associated with high gene flow in both the NP and PP groups.In order to discover superior varieties or series of H.ammodendron,ISSR analysis was used to study the genetic differentiation of F1 generation of H. ammodendron seeds.H.ammodendron seeds were carried in "Shenzhou No.4" spaceflight.The seeds and the ground-based control were also planted on the ground. The young fresh shoots of plants were used to do ISSR analysis.Ninety-four ISSR primers were used in this study,among which 80 primers generated the same DNA band type,and 14 primers generated different DNA band types.Compared with the control,six ISSR specific markers were obtained,namely UBC834-1000bp, UBC834-1200bp,UBC840-3000bp,UBC841-2000bp,UBC-842-2000bp and UBC846-1100bp.At the same time,we found that H.ammodendron carried by spaceship was superior the control group in the resistance to powdery mildew.The results in this paper provided the basis for the strong resistence to powdery mildew of H.ammodendron new varieties.