Detection of a Phytoplasma in Citrus Showing Huanglongbing (Yellow Shoot Disease) Symptoms in Guangdong, P. R. China
Citrus Huanglongbing (HLB) or yellow shoot disease (ex. greening disease) is highly destructive to citrus production worldwide. Understanding the etiology of HLB is critical for managing the disease. HLB is currently known to be associated with infection by Candidatus Liberibacter asiaticus in China. However, Kochs postulates have not been fulfilled. In addition, other plant pathogens may be also involved in HLB. In a survey performed in Guangdong Province, P. R. China in 2006 and 2007, 141 citrus samples showing typical symptoms of HLB from 11 different cities were collected. PCR using phytoplasma-specific primer sets fU5/rU3 nested with primer set P1/P7 identified 110 (78. 0％)positive samples. A 1,785 bp amplicon was obtained with primer set P1/P7. Analysis showed a 100％ identity of this sequence in the region of 16S rDNA and 16S-23S intergenic spacer to three strains of Candidatus Phytoplasma asteri onion yellows (Japan) , aster yellows watercress (Hawaii) , and valeriana yellows (Lithuania) . Of the 141 samples, 89 (63. 1％)samples were positive for Ca. Liberibacter asiaticus alone. Sixty-nine (48. 9％)of the samples was positive for both phytoplasma and Ca. L. asiaticus. Transmission electron microscopy (TEM) showed the presence of both walled and wall-less bodies in symptomatic citrus tissue but at low titer. The presence of phytoplasma with HLB was further demonstrated using the model host periwinkle Catharanthus roseus (L.)G. Don. . HLB-associated bacteria were transmitted from symptomatic citrus to periwinkle through dodder (Cuscuta campestris Yunck). PCR detected the same phytoplasma as those in citrus from the affected periwinkle, along with Ca. L. asiaticus. In addition to yellowing/mottling, the infected periwinkle showed symptoms of virescence and phyllody which are associated commonly with phytoplasmal diseases. TEM analysis of affected periwinkle revealed pleomorphic and wall-less organisms, characteristic of phytoplasmas, within some phloem sieve tubes. This study showed that in addition to Ca. L. asiaticus, a phytoplasma related to Ca. P. asteri could also be associated with citrus showing HLB symptoms in Guangdong.
Huanglongbing Phytoplasma PCR detection Guangdong
Jianchi Chen Xuelian Pu Xiaoling Deng Shizhe Liu Huaping Li Edwin Civerolo
USDA-ARS, Parlier, California, USA Citrus Huanglongbing Research Laboratory, Department of Plant Pathology Department of Soil Science, South China Agricultural University, Guangzhou, Guangdong 510642,P. R. C
国际会议
11th International Citrus Congress(第11届国际柑橘大会)
武汉
英文
1000-1007
2008-10-01（万方平台首次上网日期，不代表论文的发表时间）