基于原噬菌体类型的我国柑橘黄龙病菌种群遗传结构分析

Population genetic structure of ’Candidatus Liberibacter asiaticus’ in China based on the prophage types

柑橘黄龙病是柑橘生产上最严重的病害之一,由难培养的候选韧皮部杆菌亚洲种('Candidatus Liberibacter asiaticus',CLas)引起。目前,已报道的与CLas相关的原噬菌体有3种,并且不同的CLas样品中可以检测到不同类型的原噬菌体或不同类型的组合。本研究基于原噬菌体类型特异引物对从我国南方8省收集的548个黄龙病样品进行原噬菌体类型的鉴定和分析。结果表明,基于原噬菌体类型,在548个样品中共鉴定了7种类型的菌株,分别为Type 1(7.12%)、Type 2(60.22%)、Type 3(3.83%)、Type 1+Type 2(3.28%)、Type 1+Type 3(17.34%)、Type 1+Type 2+Type 3(3.47%)和None类型(不含上述3种类型原噬菌体)(4.74%),其中只携带Type 2类型原噬菌体菌株为华南地区优势种群。此外,基于遗传多样性和遗传距离对我国南方地区的CLas种群进行种群结构分析发现,我国南方地区的CLas种群可以分为3个组,即Ⅰ组(广东、江西、广西、福建)、Ⅱ组(浙江和湖南)以及Ⅲ组(云南和海南),其中Ⅰ组和Ⅱ组又可聚为一大组。该结果可为研究我国柑橘黄龙病流行规律提供一定的理论基础。

Citrus Huanglongbing(HLB),one of most destructive disease worldwide,is associated with an uncultivable bacterium in theα-Proteobacteria,‘Candidatus Liberibacter asiaticus’(CLas).Three types of prophages,Type 1(SC1-like),Type 2(SC2-like)and Type 3(P-JXGC-3),as well as different combinations of above prophages have been identified in CLas samples.In this study,a total of six type-specific primer sets(two sets for each prophage type)from our previous study were selected to perform the prophage typing using548 CLas samples collected from eight provinces in southern China.Based on the prophage typing profiles,seven combinations of CLas prophages were identified,including single Type 1(7.12%),single Type 2(60.22%),single Type 3(3.83%),Type 1+Type 2(3.28%),Type 1+Type 3(17.34%),Type 1+Type 2+Type 3(3.47%)and None type(4.74%).The CLas samples only harboring the Type 2 prophage were predominant in CLas population in Southern China.Genetic structure of CLas population was evaluated by using Nei’s diversity index(H value),genetic identity and genetic distance.Three major groups were identified based on the genetic distance of CLas population from eight provinces,i.e.groupⅠ(Guangdong,Jiangxi,Guangxi and Fujian),groupⅡ(Zhejiang and Hunan)and groupⅢ(Yunnan and Hainan).GroupⅠand GroupⅡcan be further clustered into a larger group.The results provide a theoretical basis for studying the epidemic of citrus Huanglongbing in China.