Analysis of population dynamics of citrus Huanglongbing in Gannan based on three prophage genes
Citrus Huanglongbing(HLB)has caused significant economic losses to the global citrus industry.This study aimed to elucidate the molecular characteristics and transmission dynamics of prophages region on genome of pathogen causing citrus Huanglongbing disease in Gannan.A total of 470 samples collected from ten counties and urban areas in Gannan were tested for HLB.The sequences of SC1_gp050,SC2_gp040 and PJXGC_gp08 genes on three types of prophages(SC1,SC2 and P-JXGC-3)were analyzed for genetic diversity and genealogical geography.The results showed that 74 samples were HLB-positive,including seven prophage combination types:SC1,SC2,P-JXGC-3,SC1+SC2,SC1+P-JXGC-3,SC2+P-JXGC-3 and SC1+SC2+P-JXGC-3.The prophages containing SC2 type(41)were the most prevalent in Gannan,with a detection rate of 55.41％.The results of genetic diversity analysis showed that the genes of the three types of prophages in the Gannan region were frequently exchanged,and genetic differentiation was not obvious.The results of selection pressure analysis showed that both SC1 and P-JXGC-3 type prophages were under negative selection,while SC2 type prophage was under positive selection.An intermediary network and haplotype distribution table based on the prophage genes revealed that three prophages were derived from one ancestral haplotype,respectively,and mutated multiple times,with the PJXGC_gp08 gene producing the most unique haplotypes.The results of spatio-temporal dynamic analysis showed that there were two transmission pathways for SC1 type prophage,involving mutual transmission between Anyuan and Quannan areas(3＜BF＜20),with Anyuan area potentially being the main dispersal location.In addition,there exist three transmission pathways for P-JXGC-3 type prophage,with Ruijin possibly being the dispersal center.The above research results provide a reference basis for analyzing the genetic evolution and dispersal dynamics of Candidatus Liberibacter asiaticus in the Gannan region.
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