The Genetic Structure And Phylogenetic Relationship Of Spodoptera Exigua In Western China

The beet armyworm,Spodoptera exigua?Hübner?,is an important and cosmopolitan pest that attacks cultivated crops,including maize,cotton,soybeans,beet,tomato,cabbage and alfalfa,causing serious economic losses in some of the main crop-producing areas.Recently,with global climate warming and the adjustment of agriculture planting structures,S.exigua has quickly spread to the main crop-producing areas of north China.Because the beet armyworm has the longest migration distance,it is difficult to control.And the genetic research of S.exigua in western China is still blank.This study aims to identify the genetic diversity and population genetic structure of S.exigua in western China by using microsatellite?SSR?molecular marker technology.The genetic diversity,genetic differentiation and population genetic structure were analyzed based on 14 geographic populations of S.exigua in western China and 2 populations in Pakistan.The results of this study were as follows:?1?The allelic diversity of S.exigua in western China was abundant?A=2.5-8.875?.The allele diversity of Yunnan Kunming?KM?and Pakistani Faisalabad?BF?populations were the highest,and the allelic diversity of Inner Mongolia Baotou?NMBT?,Qinghai Delingha?DLH?populations were relatively low.A few populations deviated from the Hardy-Weinberg equilibrium and showed a positive deviation,indicating that the heterozygotes were missing.Most populations did not deviate from the Hardy-Weinberg equilibrium at each locus.The values of allele diversity of S.exigua in different population was Southwest China>Pakistan>Northwest China>Inner Mongolia.?2?The 8 pairs of primers provided rich polymorphism information in 16 populations.The genetic diversity of 8 microsatellite loci were higher?Na=5.422,Ne=3.041,Ho=0.518,He=0.533?,thus,these SSR loci had high effectiveness and reliable genetic diversity.Among the16 geographical populations in western China,relatively moderate levels of genetic diversity for the total populations in these study regions were detected.Among them,Kunming?KM?population had the highest genetic diversity,and the Qinghai Xining?XN?and Baotou?NMBT?populations had lower genetic diversity.The type of southwestern population was higher than that in north China.Overall,the genetic diversity of S.exigua in different geographical population was:Southwest China>Pakistan>Northwest China>Inner Mongolia.?3?In all the 16 geographical populations,Baotou?NMBT?and Kunming?KM?populations differentiated were significantly(F_ST=0.262),Baotou?NMBT?and Pakistani Faisalabad?BF?populations(F_ST=0.263)differentiated were significantly,Xinjiang Korla?KEL?populations and all other populations showed significant differentiation(F_ST>0.25).Additionally,Korla?KEL?population had very low levels of communication with other populations.From the correlation analysis of geographical distance and genetic differentiation,between geographical distance and genetic differentiation,there was no significant correlation,indicating that beet armyworm had a high degree of migratory?R²=0.0436,P=0.170?.?4?Phylogenetic tree based on Nei's genetic distance,STRUCTURE cluster analysis and PCo A analysis showed that Chifeng?NMCF?,Baotou?NMBT?,Ximeng?NMXM?,Gansu?GS?,Yinchuan?YC?,Shihezi?SHZ?,Xining?XN?,Delingha?DLH?,Guiyang?GZ?,Chengdu?SC?,Multan?BM?and Faisalabad?BF?had 12 populations Similar genetic structure,Shanxi Dali?DL?,Zhaotong?ZT?and Kunming?KM?populations had similar genetic structures,and the Korla?KEL?population had an independent genetic structure.What's more,the AMOVA divergence analysis showed that the genetic variation of S.exigua in the western region of China was mainly from the inside of the population,and the level of genetic variation among the populations was relatively low.?5?The 16 populations of S.exigua in western China had reached equilibrium under the S.M.M?stepwise mutation?model and had not experienced bottlenecks.