First Report of “Candidatus Liberibacter solanacearum” on Tomato in El Salvador

Abstract

In April of 2012, tomato plants (Solanum lycopersicum) grown near the town of Yuroconte in the municipality of La Palma, Chalatenango, El Salvador, were observed with symptoms resembling those of “Candidatus Liberibacter solanacearum” infection. The symptoms included overall chlorosis, severe stunting, leaf cupping, excessive branching of axillary shoots, and leaf purpling and scorching (1,2,3). Disease incidence in several fields in the area ranged from 40 to 60%. Heavy infestations of the potato/tomato psyllid, Bactericera cockerelli, were observed in the affected fields and this insect has been shown to transmit “Ca. L. solanacearum” to tomato and other solanaceous species (1,2,3). Leaf samples and psyllids were collected from one of the fields and total DNA was purified from the leaves of 8 and 10 symptomatic and asymptomatic plants, respectively (2,3). DNA was also extracted from the psyllids and the samples were tested by PCR for species confirmation. PCR oligonucleotide primers specific for both 16S rDNA (OA2 and OI2c) and a gene for a surface antigen for the outer membrane protein (OMB) (OMB 1482f and 2086r) of “Ca. L. solanacearum” were used to confirm the presence of the bacterium in infected tomatoes (1). Four of the eight symptomatic tomatoes (50%) tested positive for “Ca. L. solanacearum” using both primer pairs and all asymptomatic plants were negative for the bacterium. The collected psyllids were first identified through a morphological key, then verified using species-specific PCR primers (CO1 F3 and CO1 meltR) that generated a 94-bp fragment that was consistent with DNA from B. cockerelli (4). Amplicons generated with DNA from two plant samples with each primer pair were cloned and four clones of each of the four amplicons were sequenced. BLASTn analysis of the 16S rDNA consensus sequences from the clones (1,168 bp; deposited in GenBank as Accession Nos. KC768318 and KC768319) showed 100% identity to “Ca. L. solanacearum” sequences in GenBank (HM246509 and HM245242, respectively). Two OMB consensus sequences were 98% identical (deposited in GenBank as KC768326 and KC768327) and both sequences were 97 to 100% identical to a number of “Ca. L. solanacearum” sequences in GenBank (e.g., CP002371, FJ914617, JN848754, and JN848752). To our knowledge, this is the first report of “Ca. L. solanacearum” associated with tomato in El Salvador and the first formal report of the bacterium in the country. This bacterium has caused millions of dollars in losses to the tomato industry in New Zealand, Mexico and the United States (2,3). Tomatoes are an economically important commodity in Central America and are severely damaged by “Ca. L. solanacearum” infection. The confirmation of “Ca. L. solanacearum” infections in El Salvador alerts the agricultural sector to the presence of this serious pathogen. References: (1) J. M. Crosslin. Southwest. Entomol. 36:125, 2011. (2) L. W. Liefting et al. Plant Dis. 93:208, 2009. (3) J. E. Munyaneza et al. Plant Dis. 93:1076, 2009. (4) K. D. Swisher et al. Environ. Entomol. 41:1019, 2012.