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Logo of bmcmicrBioMed Centralsearchsubmit a manuscriptregisterthis articleBMC Microbiology
BMC Microbiol. 2012; 12: 39.
Published online Mar 20, 2012. doi:  10.1186/1471-2180-12-39
PMCID: PMC3368738
Multilocus microsatellite analysis of 'Candidatus Liberibacter asiaticus' associated with citrus Huanglongbing worldwide
Md-Sajedul Islam,#1 Jonathan M Glynn,#1 Yang Bai,#2 Yong-Ping Duan,3 Helvecio D Coletta-Filho,4 Gopal Kuruba,5 Edwin L Civerolo,1 and Hong Lincorresponding author1
1USDA-ARS San Joaquin Valley Agricultural Research Science Center, Parlier, CA 93648, USA
2Guangxi Citrus Research Institute, Gulin, Guangxi 530004, China
3USDA-ARS Horticultural Research Laboratory, Fort Pierce, FL 34945, USA
4Instituto Agronômico de Campinas, Cordeirópolis, CEP 13490-970 São Paulo, Brazil
5Citrus Research Station, Andhra Pradesh Horticultural University, Tirupati 517502, Andhra Pradesh, India
corresponding authorCorresponding author.
#Contributed equally.
Md-Sajedul Islam: M.Sajed/at/; Jonathan M Glynn: glynnjon/at/; Yang Bai: baictj/at/; Yong-Ping Duan: yongping.duan/at/; Helvecio D Coletta-Filho: helvecio/at/; Gopal Kuruba: headcrs_tirupati/at/; Edwin L Civerolo: emciv/at/; Hong Lin: hong.lin/at/
Received September 5, 2011; Accepted March 20, 2012.
Huanglongbing (HLB) is one of the most destructive citrus diseases in the world. The disease is associated with the presence of a fastidious, phloem-limited α- proteobacterium, 'Candidatus Liberibacter asiaticus', 'Ca. Liberibacter africanus' or 'Ca. Liberibacter americanus'. HLB-associated Liberibacters have spread to North America and South America in recent years. While the causal agents of HLB have been putatively identified, information regarding the worldwide population structure and epidemiological relationships for 'Ca. L. asiaticus' is limited. The availability of the 'Ca. L. asiaticus' genome sequence has facilitated development of molecular markers from this bacterium. The objectives of this study were to develop microsatellite markers and conduct genetic analyses of 'Ca. L. asiaticus' from a worldwide collection. Two hundred eighty seven isolates from USA (Florida), Brazil, China, India, Cambodia, Vietnam, Taiwan, Thailand, and Japan were analyzed.
A panel of seven polymorphic microsatellite markers was developed for 'Ca. L. asiaticus'. Microsatellite analyses across the samples showed that the genetic diversity of 'Ca. L. asiaticus' is higher in Asia than Americas. UPGMA and STRUCTURE analyses identified three major genetic groups worldwide. Isolates from India were genetically distinct. East-southeast Asian and Brazilian isolates were generally included in the same group; a few members of this group were found in Florida, but the majority of the isolates from Florida were clustered separately. eBURST analysis predicted three founder haplotypes, which may have given rise to three groups worldwide.
Our results identified three major genetic groups of 'Ca. L. asiaticus' worldwide. Isolates from Brazil showed similar genetic makeup with east-southeast Asian dominant group, suggesting the possibility of a common origin. However, most of the isolates recovered from Florida were clustered in a separate group. While the sources of the dominant 'Ca. L. asiaticus' in Florida were not clearly understood, the less-pervasive groups may have been introduced directly from Asia or via Brazil. Notably, the recent outbreak of HLB in Florida probably occurred through multiple introductions. Microsatellite markers developed in this study provide adequate discriminatory power for the identification and differentiation of closely-related isolates, as well as for genetic studies of 'Ca. L. asiaticus'.
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