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Ultrastructural Changes and Putative Phage Particles Observed in Sweet Orange Leaves Infected with ‘Candidatus Liberibacter asiaticus’

March 2015 , Volume 99 , Number  3
Pages  320 - 324

S. M. Fu, College of Plant Protection/Citrus Research Institute of Southwest University, Chongqing 400715, P. R. China, USDA-ARS Molecular Plant Pathology Laboratory, Beltsville, MD; John Hartung, USDA-ARS Molecular Plant Pathology Laboratory, Beltsville, MD; and C. Y. Zhou, H. N. Su, J. Tan, and Z. A. Li, Citrus Research Institute, Southwest University, Chongqing 400715, P. R. China

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Accepted for publication 16 September 2014.

Huanglongbing (HLB), also known as citrus greening, is currently the most destructive citrus disease. Anatomical analyses of HLB-affected sweet orange were carried out by light and electron microscopy. As compared with healthy citrus, the phloem plasmodesmata were plugged with callose, and in some samples the phloem was collapsed. Chloroplast structures were deformed. Prophage sequences occupy a significant portion of the genome of ‘Candidatus Liberibacter asiaticus’ and have been used to distinguish strains from Yunnan and Guangdong provinces in China and Florida. Interestingly, a large number of possible putative phage particles were observed attached on the surface of ‘Ca. L. asiaticus’ cells in plants inoculated with strain FJ3 from Fujian Province, China. Phage particles have been observed previously only in periwinkle plants artificially inoculated in Florida with ‘Ca. L. asiaticus’ that carried the SC1-type prophage. PCR assays verified the presence of the SC1-type prophage sequences previously described from this bacterium in Florida in the FJ3 isolate. This is the first time that suspected phage particles have been observed in sweet orange trees infected with ‘Ca. L. asiaticus.’

This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 2015.