| Spider mite is a polyphagous pest that harms many economic crops such as corn,cotton,tomatoes,soybeans,apples,roses,etc.It has the characteristics of short generation cycle,strong adaptability,rapid population expansion and rapid evolution of resistance to pesticides,which seriously threaten agricultural production.There are about 7 common species of spider mites in my country,and the types of spider mites are often different in different regions and crops.At present,there is still a lack of systematic investigation and mechanism research on the occurrence of spider mites.This study initially investigated the species of spider mites on different crops in 10 provinces in my country,studied the diversity and genetic differentiation of different populations through mitochondrial COI genes,and selected two dominant pest mites—T.truncatus and T.pueraricola performed whole-genome sequencing and preliminary comparative genome analysis,aiming to reveal the molecular mechanism of spider mite strong host adaptation.The main conclusions are as follows:(1)Through surveys on the occurrence of spider mites in common crops in 10 provinces in China,it is found that the distribution of spider mites is the most widespread in the country,both in the north and the south;T.kanzawai is more distributed in the south,in Ningbo,Zhejiang It has been found in Fuquan,Guizhou;the T.urticae is concentrated in Yunnan,Guizhou and other regions in the south.There are many species of spider mites in the middle and lower reaches of the Yangtze River,such as Zhejiang and other places.In addition to common spider mites,there are also T.pueraricola and T.phaselus,which may be related to climate and geographical environment,more conducive to the growth and development of spider mites.Phylogenetic analysis of the COI sequence of the spider mites revealed that the T.pueraricola are closely related to the T.urticae,while the T.truncatus are closely related to the T.kanzawai.The COI haplotype genetic analysis of 9 geographical populations of T.truncatus found that the number of Hap-1 was the largest,followed by the Hap-2 haplotype.The genetic diversity of the northern population of T.truncatus was higher,and the geographical populations The overall haploid diversity of Hd is 0.7376,and the nucleotide diversity(л)is 0.00367.The place with the highest haplotype diversity is the population of Shenyang,Liaoning.According to the genetic differentiation index,the differentiation index between the northern and southern populations of T.truncatus according to geographical location is higher,with Fst of 0.313,indicating that the gene flow level of the populations in the northern and southern regions is low and increases with geographic distance,the gene flow gradually decreases.(2)Sequencing the whole genomes of T.truncatus and T.pueraricola showed that the genome size of the assembled T.truncatus was 92.89 Mb,the number of Scaffolds was 167,the N50 was 21 Mb,and the predicted CDS number was 15,820;the size of the genome of T.pueraricola was approximately 80.00 Mb,N50 is 1 Mb,the number of Scaffolds is 180,and the number of CDS is predicted to be 13,312.The splicing integrity of the T.pueraricola genome sequencing is higher than that of the T.truncatus.The estimation and analysis of the divergent evolution time of different species showed that the T.pueraricola are more closely related to the T.urticae,the divergence time is about 30.82 million years ago,while the T.truncatus and the two are about 32.53 hundred.Genome collinearity analysis showed that most of the genes of the T.pueraricola are located on the first 5longest Scaffolds,and there are more collinearity regions with the 3 chromosomes of the T.urticae,which is consistent with the results of the evolutionary tree,and jointly confirmed the two close relationship between the mites.The assembly effect of T.truncatus is poor,the Scaffolds are shorter,the collinearity with T.urticae is poor,and there are significant structural variations.This may be related to the genetic relationship between T.truncatus and T.urticae.The three species of spider mites have obvious variations in the number of genes in the P450 family of detoxification and metabolic enzymes.The T.urticae have 78P450 genes,ranking first in the number of these three spider mites,the T.pueraricola have69,and the T.truncatus are 64 spider mites.The phylogenetic analysis of the P450 family found that the CYP2 and CYP4 subfamily had more genes in the three species of spider mites,and the T.urticae expanded more significantly in the CYP2 subfamily than the other two species.The T.urticae were in CYP2.The number of genes in is 38,the T.pueraricola have 22,and the T.truncatus have 22. |
