| Myzus persicae(Hemiptera: Aphididae), the peach-potato aphid, is a cosmopolitan, economically important pest of agriculture, horticulture and tobacco. Population genetic structure and genetic differentiation may result from restricted gene flow among local populations due to regional variations in environmental conditions. However, due to factors, such as demographic events associated with the plasticity of reproductive modes, host specialization and the alternation between primary and secondary hosts, M. persicae among different geographic populations is characterized by a high genetic variation.In this thesis, we focused on the scientific issue on population genetic structure of M. persicae and the researches including screening some highly polymorphic microsatellite markers for research on the population genetic structure of M. persicae; studying of population genetic diversity, genetic structure and the phylogenetic tree of M. persicae in southwest tobacco-growing areas and different host plants. The objectives of the thesis are to explore genetic differentiation and host specialization of M. persicae among different geographic populations in Chongqing and southwest tobacco-growing areas, to uncover the differential law and mechanism, and to provide a scientific basis for the pest monitoring and integrated control. The main results are as follows: 1. Screening of microsatellite markers in M. persicaeThe objective of the study is to screen some highly polymorphic microsatellite markers for research on the population genetic structure of M. persicae. 65 pairs of microsatellite primers were selected. The polymorphism information content(PIC), Nei’s genetic heterozygosity(h) and effective number of alleles(Ne) and so on were used for analysis. The results showed that 29 pairs of microsatellite primers among 65 pairs could amplify the genomes of M. persicae specifically, and the homologous rate was 44.62 %. 78 alleles were detected at 11 microsatellite locus in M. persicae, and the average number of alleles was 7.0909. The average polymorphism information content of 11 microsatellite primers was 0.3494, the average effective number of alleles was 5.4464, the average Nei’s genetic heterozygosity was 0.7295. The screened 11 microsatellite primers of M. persicae showed a good polymorphism, and could be used in the subsequent research. 2. Population genetic structure analysis of M. persicae in Chongqing tobacco-growing areas.We used microsatellite DNA markers to compare the genetic diversity and differentiation of M. persicae populations of 10 major tobacco-growing areas in Chongqing district. The results suggested that Shannon’s information index of 10 populations of M. persicae ranged from 0.3740 to 0.6127 with an average of 0.4929, Nei’s genetic heterozygosity ranged from 0.1937 to 0.3188 with an average of 0.2563. The mean observed and expected heterozygosity were 0.3524 and 0.2659, indicating the excess of heterozygotes. Fst ranged from 0.5493 to 0.7865 and gene flow(Nm) was less than 1, which reflected an extreme genetic differentiation and a low level of Nm among all the populations. AMOVA attributed about 55.91 % of the variance to among populations within groups, indicating that the mainly genetic variation existed among different populations. Mantel tests demonstrated that there was no significant correlation between genetic and geographic distances(r=0.0945, P=0.6883), as well as between genetic identity and elevation(r=-0.1755, P=0.8322). The UPGMA phylogenetic, Structure and PCA analysis showed that the 10 geographic populations in Chongqing tobacco-growing areas were clustered into three groups. 3. Population genetic diversity and genetic differentiation analysis of M. persicae in southwest tobacco-growing areas.SSR molecular marker technology was used for genetic diversity analysis of M. persicae populations from 8 tobacco-growing areas, including Chongqing district, Guizhou Province, Sichuan Province, Hubei Province and Yunnan Province. Our results indicated that there existed a high level of genetic diversity among different geographic populations of M. persicae(I=0.6166, He=0.3383), an extreme genetic differentiation and a low level of Nm among all the populations(Fst: 0.4894-0.6901, Nm﹤1). AMOVA attributed about 45.06 % of the variance to among different populations within groups, indicating that the main genetic variation existed among populations. A positive correlation(r=0.4554, P=0.0220) was detected between genetic and geographical distances of populations by Mantel test. The UPGMA phylogenetic, Structure and PCA analysis showed that the 8 geographic populations in southwestern tobacco-growing areas were clustered into two groups, and the clustering results maintained a certain regularity in the natural geographical distribution. 4. Population genetic diversity of M. persicae from different host plants and host specializationMicrosatellite molecular marker technology was used for genetic diversity analysis of M. persicae populations from 5 host plants. The results showed that the genetic diversity of the population of M. persicae on different host plants were: Brassica campestris L. ﹥ Capsium tuberowsum L. ﹥ Raphanus sativus L. ﹥ Vicia faba L. ﹥Nicotiana tabacum L., and there existed an extreme genetic differentiation and a low level of Nm among all the populations(Fst: 0.4891-0.6922, Nm﹤1). AMOVA showed that the main genetic variation existed among different host plants. The UPGMA phylogenetic, Structure and PCA analysis showed that the 5 populations from different host plants were clustered into two groups. The formation of a host specialization type in Chongqing tabacco-growing areas may be produced by the low level of Nm, the obligate parthenogenesis, the host adaptability and so on. |
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