| Potato is not only the the fourth largest grain crop of the world, after rice, wheat and maize, but also an important forage crop and raw material for chemical industry. China is the largest potato producer in the world, its production related to food security of the country and even the world. Aphids is one of the most important virus-vector insect and migration pest attacking potato, with the characteristic of large numbers and dispersed distribution. Colonies of the aphid not only feed upon the potato leaves, but also transmit a variety of plant virus, influencing the normal growth of plant, leading to decrease of yield and quality, resulting in variety degradation of potato, therefore, effective control of aphids is the key step of potato production. Influenced by long-term environmental stress and host selection pressure, different geographical populations and host populations of aphids emerged genetic differentiation, which has formed the new adaptability popuation of aphids. However, the migration of aphids enhances the genetic exchange among the populations to a certain extent, decreased the level of genetic differentiation. To make in-depth research on genetic structure of aphids dominant species, on reproductive isolation and genetic exchange among of the populations, which is beneficial to reveal the mechanism of adaptability and disaster, and provide a basis for correct understanding of occurrance and effective controlling on aphids of potato. In this paper, genetic diversities of different host-population and geo-population of dominant species of potato aphids Myzus persicae were studied by SSR-PCR, the purpose of this study was to compare genetic similarity, understand gene flow, analyse the possible migration routes, estimate the possible emigratory areas and ingoing areas of different population of Myzus persicae aphids of potato, and provide theoretical basis for regional control of aphids. The important results are shown as follows:1. The results of morphological identification in Tianshui, Dingxi and Zhangye of Gansu province showed that the main species of aphids on potato were Myzus persicae, Aphisgossypii, Brevicoryne brassicae, Lipaphis erysimi, Acyrthasiphon pisum, and Macrosiphum sp, the dominant specie is Myzus persicae, which is the most important mediator about transmitting virus of potato.2. The method of"improved KAC"were adopted to extract the genomic DNA of single-aphid, this method was optimised as follows:disposable and sterilized toothpicks were used to break up the cells, which can prevents cross-contamination risk. proteinase K were used, prolong the time of water bath was used to improve digest aphids and break down of RNA when homogenate of single-aphid were extracted. To increase DNA yield rate by the steps of balanced phenol and chloroform were canceled,and the DNA precipitation time was prolonged. This method is ideal way to extract the genomic DNA of aphid,because of simple operation and undemanding equipment, it also could solve the problem that extracting of genomic DNA of single-aphid was difficult and unstable.3. The reaction conditions of SSR experiment of Myzus persicae were discussed, and the results showed the components of optimal concentration SSR reaction system of 20μL as follows: Mg2+ 1.5mM,Deoxyribonucleotide triphosphate 0.25mM,Taq DNA Polymerase 1.0U/μL,DNA template 40ng/μL,primers 25ng/μL, which was a basis for the study on genetic divergency of Myzus persicae populations.4. Screened 14 pairs of highly polymorphic primers from 46 pairs of primers for aphids and analyzed the genetic relationship of peach,tobacco,cabbage,pepper and potato,which were the host-plants of Myzus persicae. The result of this analysis showed that 70 polymorphic bands were detected using 14 pairs of SSR primers in the five populations,percentage of polymorphic bands were 98.59%,the molecular weight of DNA fragments were from 70bp to 300bp. 29 polymorphic loci of Myzus persicae detected from the population of potato was mostly, 6 polymorphic loci from cabbage was leastly. The Shannon-Wiener diversity and Nei's genetic diversity indexes were respectively 0.5382 and 0.3631, the gene flow was 0.1343 amomg population, there is an tendency of Myzus persicae population diversity in 5 host plants, the popato>the peach>the tobacco>the pepper>the cabbage, and the genetic variation was mainly the inner of population. Using UPGMA method, the relationship between two host-populations of Myzus persicae on tobacco and pepper are the closest, and the farthest is potato, which indicated that the evolution of Myzus persicae is towards the direction of keeping away from tobacco and pepper.5. Seven highly polymorphic SSR primers were employed to investigate the genetic variation and structure of thirteen populations of potato aphids Myzus persicae from Zhangye, Wuwei, Jiuquan, Lanzhou, Lintao, Linxia, Dingxi, Zhangxian, Weiyuan, Minxian, Tianshui, Wudu and Qingyang in Gansu province. The result showed that 43 polymorphic locus were detected using 7 pairs of SSR primers in the 468 individuals of 13 populations,percentage of polymorphic bands were 95.56%. The number of observed alleies was 1.3333, and that of effective alleles was 1.2293, the Nei's genetic diversity and Shannon-Wiener diversity indexes were respectively 0.1311 and 0.1898, percentage of polymorphic locus were 33.33%. The gene flow was 0.3027 amomg population. The population genetic diversity of Linxia and Lintao were higher, Zhangxian was lower. The genetic distance is the nearest between Zhangye and Wuwei, it is the farthest between Zhangye and Qingyang. Analysis of molecular variance showed that 81.03% genetic variation existed within the populations of Myzus persicae on potato. Mantel-test showed that genetic distances had no significant correlation with geographic distance and gap of elevation among popuations.6. The cluster analysis showed that the potato aphids Myzus persicae collected from Gansu province could divide into two groups of Hexi and Hedong which of the boundary was the Huanghe River. Hexi group included with Zhangye, Jiuquan, Wuwei and Lanzhou population, in the Hedong group, Dingxi, Qingyang and Huichuan were classified one cluster that located east-central of Gansu province; Tianshui, Wudu and Minxian were southeast; Zhangxian, Lintao and Linxia were individually. A further analysis showed that there were two natural ingoing paths of the potato aphids Myzus persicae located midland of Gansu province where potato is the main crop, one maybe migrate from Qingyang located east of Gansu,the other maybe from Tianshui located southeast of Gansu,then Myzus persicae dispersed from midland to southwest of Gansu province. The relevance of the former was significant than latter. From this, we could infer that main native area of potato aphids Myzus persicae maybe north of Shanxi and east of Gansu, secondary area maybe southeast of Gansu province. We suggest to strengthen monitoring and controlling of the potato aphids Myzus persicae in these area to reduced the quantity of overwinter and ingoing population.This study realized an organic combo of the microscopic molecular genetic and insect macroscopic morphology and ecology,which have important referential value for further to reveal the disaster mechanism and migration rule in theory,and in practice,to carry out efficiently integrated aphids control and to build reproduction base of the fine-quality potato tuber seeds.
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