First Report of Dodder Transmission of 'Candidatus Liberibacter asiaticus' to Tomato (Lycopersicon esculentum).

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.