Objective:

Develop genomic sequence information of Liberibacter variants found in California, Texas and other citrus-producing regions

• HLB is known to be caused by several species of Liberibacters. Candidatus Liberibacter asiaticus (Las) is the only reported species in the USA. However,  molecular analyses and NextGen sequencing of several isolates have enabled us to identify populations that may have resulted from separate introductions from different geographic areas. Such information is highly critical for management of disease epidemics.
• HLB was first found on one lemon tree in Hacienda Heights, CA in 2012. The second find was in 2015 in ten trees in San Gabriel, about 15 miles north of the first find site. In both cases, infected psyllids lead to infected trees. Both locations in the Los Angeles basin are from backyard trees. Liberibacter positive psyllids lead to HLB positive plants.
• Following the 2012 find, several suppression measures were enforced in the area; no new HLB finds have been reported yet from the close vicinity of the initial find. An important question is, whether the 2015 HLB find resulted because of pathogen spread from Hacienda Heights or, if it is from a different source of introduction.
• Molecular analyses and NextGen sequencing strongly suggest that the two are separate introductions. This information is encouraging for continuation of eradication and suppression efforts.
• We have found a new species of liberibacter, Candidauts Liberibacter caribbeanus from Colombia.
• So far, we have found this bacterium mostly in psyllids and in two plants.
  NextGen sequencing of this isolate has shown that it is distinct form all other known pathogenic forms of citrus liberibacters.
• Further NextGen sequencing for complete characterization of the genome is in progress.
• Molecular characterization of Las from several citrus relatives ('Indian Bael' and 'Afraegle') are also in progress.

The New Bacterium from Colombia (APS2015 PPT)