The Study Of Genetic Diversity And Prediction Potential Suitable Area Of Diaphorina Citri In China

Citrus Huanglongbing(HLB)is a devastating citrus disease that has caused considerable economic losses to the citrus industry worldwide,with no known cure.The disease is spread by the Asian citrus psyllid(ACP),a sap-sucking insect that feeds on Rutaceae plants,and is confirmed as a vector of HLB.This poses a severe threat to China’s citrus industry,as the ACP has shown a significant northward expansion trend in China,according to a 2014 survey conducted by the National Agro-Tech Extension and Service Center(NATESC).To protect HLB-free citrus regions from ACP infestation,it is crucial to establish a quarantine zone for the insect.Genetic diversity studies conducted on ACP samples collected from different geographic populations have revealed the level of genetic differentiation among them,as well as population expansion trends.Additionally,research on the potential distribution areas of ACP has identified significant environmental factors influencing their expansion.The findings of these studies provide scientific data support for the establishment of a quarantine zone for the Asian citrus psyllid.In this dissertation,the genetic diversity of the Asian citrus psyllid in China was preliminarily revealed by cross-analysis on 570samples and downloaded sequences from Gen Bank based on mitochondrial gene COI and the gene of primary endosymbiont Candidatus Carsonella ruddii(C.ruddii)of ACP via phylogenetic methods.The potential suitable areas of the Asian citrus psyllid under current conditions were predicted by analyzing distribution data of ACP and 16 environmental factors which influence ACP expansion in China via Bayesian Maximum Entropy Model(Max Ent Model).The specific results are as follows:1.The results of synonymous mutations(Ka)and non-synonymous mutations(Ks)in the population of the ACP in China indicate that the Ka/Ks values for both COI gene(Ka/Ks=0.5739)and C.ruddii gene(Ka/Ks=0.1925)are less than 1,suggesting that the ACP in China is under negative selection,and natural selection has inhibited the variation of dominant species.The AMOVA analysis shows that 64.11%of the genetic variation based on the COI gene of the ACP mitochondria comes from inter-population,and the rest 35.85%of the variation comes from intra-population(Fst=0.6411>0.35,P=0.0000);For C.ruddii gene of ACP,5.66%of the genetic variation comes from inter-population,and the rest 44.34%of the variation comes from intra-population(Fst=0.55663>0.35,P=0.0000).These data indicate the genetic architecture of Chinese ACP population is diverse,and most of the variation comes from inter-population.The Mental Test shows that there is a correlation between the genetic distance and the geographical distance of the Chinese ACP(R~2=0.0884,P<0.01 for COI gene;R~2=0.0726,P<0.01 for C.ruddii gene),suggesting that the spread of the ACP in China mostly natural,and there is little influenced by human intervention.2.Based on the COI gene and C.ruddii gene,two haplotype networks were constructed.In addition,two dominant haplotype H1 and C8 were found in each of these networks,mainly distributed in the southeastern region of China.The networks could be divided into Lineage A which was primarily composed of populations from the southeastern region of China and Lineage B that consist of populations from Yunnan(excluding C.ruddii haplotypes from populations in Taiwan,Fujian,and Zhejiang).These results suggest that there are two introductory zones of ACP,Guangdong and Yunnan,and the southeastern population of ACP may have migrated to the Yunnan population in the history of their expansion.3.The neutral detection of genes based on the COI gene showed that Tajima’D value was positive(D=1.38811,P>0.10),while Fu’Fs value was negative(Fs=-5.654,P=0.003),and the mismatch distribution was unimodal;Furthermore,neutral detection based on the C.ruddii gene showed negative values for Tajima’s D(D=-1.95348,P<0.05)and Fu’s Fs(Fs=-29.846,P=0.000),also showing a unimodal distribution mismatch.To summary,the both testing results indicating that the ACP experienced a significant population expansion.4.The environmental factors with highest influence on proliferation of ACP were precipitation in the warmest quarter,average temperature in the driest and coldest seasons,and precipitation in the month with greatest rainfall.In current habitat,ACP are likely to invade Chongqing,Hubei,Anhui and Jiangsu.