Abstract
BackgroundHuanglongbing (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.ResultsA 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.ConclusionsOur 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'.
Highlights
IntroductionThe disease is associated with the presence of a fastidious, phloem-limited a- proteobacterium, ‘Candidatus Liberibacter asiaticus’, ‘Ca. Liberibacter africanus’ or ‘Ca. Liberibacter americanus’
Huanglongbing (HLB) is one of the most destructive citrus diseases in the world
HLB has been known in Asian countries since the 1870s [1,5,6] and found to be associated with the presence of a fastidious a-proteobacterium named ‘Candidatus Liberibacter asiaticus’
Summary
The disease is associated with the presence of a fastidious, phloem-limited a- proteobacterium, ‘Candidatus Liberibacter asiaticus’, ‘Ca. Liberibacter africanus’ or ‘Ca. Liberibacter americanus’. HLB is associated with three ‘Candidatus Liberibacter’ species worldwide: ’Ca. L. asiaticus’, ‘Ca. L. africanus’ and ‘Ca. L. americanus’; the nomenclature is based on the presumptive origin of each bacterium in Asia, Africa and South America, respectively [1]. ‘Ca. L. americanus’ initially constituted a major proportion of the total bacterial population in Brazil, this ratio has changed since 2004, and ’Ca. L. asiaticus’ is the most prevalent citrus-destroying species [4]. L. asiaticus’ is the most prevalent citrus-destroying species [4] Both ‘Ca. L. americanus’ and ’Ca. L. asiaticus’ are transmitted by a psyllid vector, Diaphorina citri ( known as the Asian citrus psyllid, or ACP) in Asia, North America, and South America [7,8]. HLB affects all citrus cultivars [10] and to date there are no known HLB-resistant citrus cultivars
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
