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Title: A new phytoplasma associated with little leaf disease in azalea: multilocus sequence characterization reveals a distinct lineage within the aster yellows phytoplasma group

item WEI, WEI - University Of Maryland
item CAI, HONG - Yunnan Agricultural University
item JIANG, YI - South China Agricultural University
item Lee, Ing Ming
item Davis, Robert
item DING, YANG - China Agricultural University
item YUAN, ENPING - Yunnan Agricultural University
item CHEN, HAIRU - Yunnan Agricultural University
item Zhao, Yan

Submitted to: Annals of Applied Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2011
Publication Date: 3/1/2011
Citation: Wei, W., Cai, H., Jiang, Y., Lee, I., Davis, R.E., Ding, Y., Yuan, E., Chen, H., Zhao, Y. 2011. A new phytoplasma associated with little leaf disease in azalea: multilocus sequence characterization reveals a distinct lineage within the aster yellows phytoplasma group. Annals of Applied Biology. 158:318-330.

Interpretive Summary: In recent years, an increasing number of diseases in agriculturally and ecologically important plant species have been found to be caused by infection of a group of small bacteria called phytoplasmas. Phytoplasmas live inside nutrient-transporting vessels of infected plants and are spread from diseased plants to healthy ones by insects. In 2009, a new disease affecting azalea plants occurred in southeast China. Diseased plants displayed abnormal growth patterns such as excessive branching and producing very small leaves. Using DNA fingerprinting technology, we determined that the azalea disease was associated with infection by a previously unknown phytoplasma. Analysis of multiple molecular markers revealed that this azalea-infecting phytoplasma represents a new, genetically distinct branch of phytoplasmas. By revealing a new plant disease and determining its apparent cause, the work will impact plant pathological research and aid in developing strategies to control the azalea disease. This report will be of interest to diagnostics laboratories, research scientists and extension personnel who are concerned with phytoplasma disease management. The information is also important to international quarantine agencies for implementation of new quarantine regulations.

Technical Abstract: An azalea little leaf (AzLL) disease characterized by abnormally small leaves, yellowing, and witches’-broom growth symptoms was observed in suburban Kunming, southwest China. Transmission electron microscopic observations of single-membrane-bound, ovoid to spherical bodies in phloem sieve elements of diseased plants and detection of phytoplasma-characteristic 16S rRNA gene sequences in DNA samples from diseased plants provided evidence linking the disease to infection by a phytoplasma. Results from RFLP, phylogenetic, and comparative structural analyses of multiple genetic loci containing 16S rRNA, rpsS, rplV, rpsC, and secY genes indicated that the AzLL phytoplasma represented a distinct, new 16Sr subgroup lineage, designated as 16SrI-T, in the aster yellows phytoplasma group. The genotyping also revealed that AzLL phytoplasma represented new rp and secY gene lineages [rp(I)-O and secY(I)-O, respectively]. Phylogenetic analyses of secY and rp gene sequences allowed clearer distinctions between AzLL and closely related strains than did analysis of 16S rDNA.