Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2007
Publication Date: 4/15/2007
Citation: Deng, X., Chen, J., Feng, Z., Shan, Z., Guo, H., Li, H., Civerolo, E.L. 2007. Identifiction and Characterization of Huanglongbing Bacterium in Pummelo [citrus grandis (L.) Osbeck] from Multiple Locations in Guangdong, P.R. China. Plant Disease. 92:513-518. Interpretive Summary: Citrus huanglongbing (HLB) or citrus greening disease is a highly destructive disease worldwide. The disease had not been found in the United States until 2005 when the pathogen, Candidatus Liberibacter asiaticus, was identified in Florida. Sweet orange and mandarin are particularly susceptible to HLB. In contrast, pomelo has been considered to be resistant or tolerant. This manuscript reports the results of a study on a highly popular pomelo cultivar, Shatianyou, showing leaf mottle symptoms in southern China. In addition to the description of symptomatology, PCR procedures using primers of recognized taxonomic value were utilized to identify the pathogen from diseased plants. Together with sequence analysis results based on the most recent bioinformatics data, Candidatus Liberibacter asiaticus was confirmed to be associated with pomelo leaf mottle disease. Therefore, pomelo leaf mottle is a form of HLB. The pomelo HLB could reach to the incidence of 80% in the orchard studied, leading to a severe crop loss. The new information reported in this manuscript will have impact on citrus HLB research and disease management. Based on this research, pomelo and grapefruit will have to be considered in the overall management of HLB.
Technical Abstract: Huanglongbing (HLB) or citrus greening disease, caused by Candidatus Liberibacter spp., is highly destructive to citrus production in Asia, Africa, and South America. The disease has recently been found in North America (Florida). While primarily affecting sweet orange and mandarin, HLB has been suspected of being associated with Shatianyou pomelo (Citrus grandis) leaf mottle disease in Guangdong, People’s Republic of China. PCR analyses on symptomatic leaves were performed using primers specific to the 16S rDNA (OI1/OI2c) and beta operon (A2/J5) of Ca. L. africanus and Ca. L. asiaticus. Primer set OI1/OI2c produced a 1,100 bp amplicon, which yielded two DNA bands of 500 and 600 bp when digested by XbaI. Primer set A2/J5 amplified a 700 bp DNA band. These results are characteristic of Ca. L. asiaticus. Identical sized products were amplified from a greenhouse-grown sweet orange (C. sinensis) tree known to have HLB, while no DNA was amplified from healthy Shatianyou. PCR amplicons were cloned and sequenced. The 16S rDNA amplicon was 1,167 bp with 99.6% - 100% similarity to those of Ca. L. asiaticus. The beta operon fragment was 703 bp with 99.8%- 100% similarity to those of Ca. L. asiaticus. This is the first report confirming the association of Ca. L. asiaticus with leaf mottle disease of Shatianyou pomelo in southern China. Although the general perception is that pomelo is resistant or tolerant to HLB, the incidence of Shatianyou pomelo leaf mottle disease in an orchard can be as high as 80% leading to a severe crop loss.