Study On The Genetic Diversity Of Lissorhoptrus Oryzophilus In Hunan Province

Rice water weevil,Lissorhoptrus oryzophilus Kuschel(Coleoptera:Curculionidae)is native in the Unites States,and was first discovered in Tanghai County of Tangshan City,China in 1988.The weevil was found in Zhuzhou,Hunan Province in 2001.Until now,it has been found in Yueyang,Changsha,Yiyang,Loudi,Shaoyang,Hengyang and other cities,and it becomes the more harmful quarantine insect pests in Hunan,even in China.Although some scholars have studied the genetic structure of rice water weevil in China,but there are few sampling points in Hunan province.To understand the genetic structure of the rice weevil in Hunan province in a comprehensive way,this study used ISSR molecular markers,mitochondrial COI gene and ITS2 sequence analysis of genetic diversity and genetic differentiation in 21 geographic populations of the rice water weevil.The main contributions of this work are as follows:(1)Genetic differentiation of 21 geographical populations was analyzed by 9 ISSR primers.The results showed that 74 bands were obtained by ISSR-PCR,among these,69 were polymorphic,and the percentage of polymorphic bands(PPB)was 93.24 %.At the level of species,the number of alleles(Na)was 1.9324,the number of effective alleles(Ne)was 1.6396,and Nei's gene diversity index(H)was 0.3630.Shannon information diversity index(I)was 0.5320.The coefficient of genetic differentiation(Gst)among populations was0.4143,the genetic identity among populations was 0.6599-0.9369,and the genetic distance was 0.0652-0.4156.Gene flow(Nm)was 0.7068.Mantel Test among groups showed that there was no correlation between genetic distance and geographical distance.Nine ISSR primers showed high polymorphism,and the gene differentiation coefficient(Gst)and gene flow(Nm)showed certain genetic differentiation among populations,the level of gene flow among populations was moderate.(2)This study obtained and analyzed partial sequence of mitochondrial COI gene in rice water weevil,which was 825 bp long.The sequence comparison showed that the mitochondrial COI gene sequence of 21 populations was exactly the same,so it was not suitable for further analysis as limited data because the gene was too conservative in the weevil.(3)According to the conserved sequences of 18 S rRNA?5.8S rRNA?28S rRNA in otherweevil insects,the ITS2 sequence of rice water weevil was amplified by designing specific primers,and the ITS2 sequences of 21 geographic populations were compared.The results showed that the ITS2 sequence didn't show polymorphism,as similar to that of COI gene sequence,ITS2 was conserved in the weevil.In this study,the experimental results showed that the mitochondrial COI gene and ITS2 sequence in rice water weevil were relatively conservative.The comparison of the mitochondrial COI gene and the ITS2 sequence of different geographic populations showed that there was no difference between the mitochondrial COI gene and the ITS2 sequence.Under the background of the weevil parthenogenesis and the invasion wasn't long enough,the mitochondrial COI gene and ITS2 sequence in the weevil might be too conservative to be studied in the genetic differentiation.However,through the study of ISSR markers on samples,it was found that there was a certain degree of genetic diversity in the samples supplied,which enriched and supplemented the study on the genetic structure of the weevil in Hunan Province.