Duan Y P, Gottwald Tim, Zhou L J, Gabriel D W
USDA-ARS-USHRL, Fort Pierce, FL 34945.
Plant Pathology Department, University of Florida, Gainesville 32611.
Plant Dis. 2008 May;92(5):831. doi: 10.1094/PDIS-92-5-0831C.
Citrus huanglongbing (HLB) is one of the most devastating diseases of citrus worldwide. The disease is associated with three different species of fastidious α-proteobacteria, namely 'Candidatus Liberibacter asiaticus', Ca. L. americanus, and Ca. L. africanus (1). 'Ca. L. asiaticus' was first detected in South Florida in 2005 and has spread throughout the citrus-growing areas of Florida. 'Ca. L. asiaticus' is transmitted naturally by the Asian citrus psyllid, Diaphorina citri, and can also be transmitted by graft propagation and via various species of dodder (Cuscuta). HLB affects most if not all citrus and citrus relatives within the family Rutaceae (2), including the ornamental shrub Murraya paniculata (4). In addition, 'Ca. L. asiaticus' and 'Ca. L. americanus' can infect tobacco (Nicotiana xanthi) and periwinkle (Catharanthus roseus) (1,4). Here we report that 'Ca. L. asiaticus' can infect tomato (Lycopersicon esculentum) cvs. Manapal and FL47. Manapal and FL 47 plants grown from seed were placed adjacent to 'Ca. L. asiaticus'-infected sweet orange (Citrus sinensis) plants with dodder (Cuscuta pentagona) already well established on them. Young dodder shoots still connected to the citrus were draped over the tomato plants and subsequently also became attached to the tomato stems. After 1 month, the tomato plants were detached from the citrus and most of the dodder removed. One month later, these tomato plants started to show vein clearing and subsequently the mature leaves became thicker and leathery. Some leaves showed blotchy mottle symptoms and some fruits became lopsided in a manner similar to HLB symptom expression on citrus. PCR amplification of the 'Ca. L. asiaticus' 16S rDNA with primers OI1/OI2c and the β-operon with primers A2/J5 (1) revealed the presence of 'Ca. L. asiaticus' DNA. Sequence analysis confirmed that the sequences of the cloned amplicons were identical to those from the HLB-infected citrus source plant. Both conventional and quantitative real-time PCR (3) revealed a much lower abundance of 'Ca. L. asiaticus' DNA in tomato as compared with 'Ca. L. asiaticus'-infected citrus or periwinkle, indicating that 'Ca. L. asiaticus' bacteria multiplied at a lower titer in these tomato cultivars. References: (1) J. M. Bové, J. Plant Pathol. 88:7, 2006. (2) S. E. Halbert et al. Fla. Entomol. 87:330, 2004. (3) W. Li et al. J. Microbiol. Methods 66:104, 2006. (4) L. Z. Zhou et al. Plant Dis. 91:227, 2007.
柑橘黄龙病（HLB）是全球最具毁灭性的柑橘病害之一。该病害与三种不同的苛求α-变形菌有关，即“亚洲韧皮杆菌”（Candidatus Liberibacter asiaticus）、美洲韧皮杆菌（Ca. L. americanus）和非洲韧皮杆菌（Ca. L. africanus）（1）。“亚洲韧皮杆菌”于2005年首次在佛罗里达州南部被发现，并已蔓延至佛罗里达州的柑橘种植区。“亚洲韧皮杆菌”通过亚洲柑橘木虱（Diaphorina citri）自然传播，也可通过嫁接繁殖以及菟丝子（Cuscuta）的各种物种传播。HLB影响芸香科中大多数（如果不是全部）柑橘及其近缘植物（2），包括观赏灌木九里香（Murraya paniculata）（4）。此外，“亚洲韧皮杆菌”和美洲韧皮杆菌可感染烟草（Nicotiana xanthi）和长春花（Catharanthus roseus）（1,4）。在此，我们报告“亚洲韧皮杆菌”可感染番茄（Lycopersicon esculentum）品种玛娜帕（Manapal）和FL47。将种子培育出的玛娜帕和FL47植株放置在已被“亚洲韧皮杆菌”感染且菟丝子（Cuscuta pentagona）已在其上良好生长的甜橙（Citrus sinensis）植株旁边。仍与柑橘相连的菟丝子嫩枝搭在番茄植株上，随后也附着在番茄茎上。1个月后，将番茄植株与柑橘分离，并去除大部分菟丝子。1个月后，这些番茄植株开始出现叶脉黄化，随后成熟叶片变厚且呈革质。一些叶片出现斑驳症状，一些果实变得畸形，其方式类似于柑橘上HLB症状的表现。用引物OI1/OI2c对“亚洲韧皮杆菌”16S rDNA进行PCR扩增，并用引物A2/J5对β-操纵子进行PCR扩增（1），结果显示存在“亚洲韧皮杆菌”DNA。序列分析证实，克隆扩增子的序列与来自感染HLB的柑橘源植物的序列相同。常规PCR和定量实时PCR（3）均显示番茄中“亚洲韧皮杆菌”DNA的丰度远低于感染“亚洲韧皮杆菌”的柑橘或长春花，这表明“亚洲韧皮杆菌”在这些番茄品种中的繁殖滴度较低。参考文献：（1）J. M. 博韦，《植物病理学杂志》88:7，2006年。（2）S. E. 哈尔伯特等人，《佛罗里达昆虫学家》87:330，2004年。（3）W. 李等人，《微生物学方法杂志》66:104，2006年。（4）L. Z. 周等人，《植物病害》91:227，2007年。
