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United States Department of Agriculture

Agricultural Research Service

Research Project: Use of Molecular Markers to Determine Genetic Relationships of Citrus and Citrus Relatives
2012 Annual Report


1a.Objectives (from AD-416):
Provide expertise in the area of genetic analysis of germplasm of citrus, citrus relatives, and date palm. This supports the mission to collect, evaluate, and distribute germplasm of citrus, citrus relatives, and date palm.


1b.Approach (from AD-416):
Use molecular markers and gene sequence information to characterize citrus, citrus relatives, and date palm accessions to help identify redundancies and gaps in the collection, screen potential new accessions, and identify important regulatory genes of metabolic pathways. Documents SCA with UC Riverside. Replaces 5310-21000-008-03S (4/08). FORMERLY 5310-21000-008-12S (8/08).


3.Progress Report:

This project is related to objectives 1 and 3 (identification of priority genetic resources of citrus and characterization of the genotype of citrus, respectively) of the parent project. Huanglongbing in citrus relatives. Citrus greening or Huanglongbing (HLB) is a devastating disease reported predominantly from Citrus species. Effective mitigation of HLB requires information on all possible means of distribution of the disease including spread by alternate hosts. Citrus relatives collected from HLB-infected regions of South Florida were analyzed for the presence of ‘Candidatus Liberibacter asiaticus’ (LAS). Quantitative real time polymerase chain reaction assay (qPCR) of the 16s RNA region indicated the presence of LAS from several plant samples. Molecular confirmation of the presence of LAS was carried out by PCR amplification, cloning and sequencing of several other genomic regions of the bacterium. The taxonomic identity of the host plant materials was confirmed by comparing the sequence of a nuclear gene, malate dehydrogenase, with the sequence of known accessions from the Citrus Variety Collection, Riverside, California. This is the first report of detection of the bacterium associated with HLB from naturally infected Atalantia ceylanica and Severinia buxifolia from the United States. The sequence information shows that Atalantia ceylanica and Severinia buxifolia harbor a bacterium identical to LAS associated with HLB. The study helps in generating information about citrus relatives that can serve as alternate hosts for LAS.


Last Modified: 10/21/2014
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