Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/2009
Publication Date: 10/21/2009
Publication URL: http://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-93-11-1216A
Citation: Ling, K., Zhang, W. 2009. First report of a natural infection by Mexican papita viroid and tomato chlorotic dwarf viroid on greenhouse tomatoes in Mexico. Plant Disease. 93:1216. Interpretive Summary: In early 2008, tomato plants (Solanum lycopersicum) grown in a large greenhouse facility located near Mexico City, Mexico exhibited general stunting, leaf chlorosis on top of the diseased plant and later turned to bronzing or purpling with reduced-size fruits. Initially, diseased plants were confined to a 5-ha greenhouse, but the disease quickly spread to two additional 5-ha greenhouses in the summer of 2008. By the end of 2008, a total of 35-ha of greenhouse tomatoes were infected. The causal agent was readily transmitted to tomato plants through mechanical inoculation. Two type of viroid sequences were identified in the diseased plants. The first type was identified as Mexican papita viroid (MPVd) and the second as Tomato chlorotic dwarf viroid (TCDVd). Identification of the presence of two different types of viroids made accurate determination of the etiology difficult. The complexity of the etiology will cause additional challenges to the tomato industry to effectively manage this emerging viroid disease.
Technical Abstract: In early 2008, tomato plants (Solanum lycopersicum) grown in a large greenhouse facility located near Mexico City, Mexico exhibited general stunting, leaf chlorosis on top of the diseased plant and later turned to bronzing or purpling with reduced-size fruits. Bioassay demonstrated the mechanical transmissibility of the causal agent to tomato plants. A pospiviroid sequence was consistently detected by RT-PCR in the diseased samples as well as in their respective inoculated plants. An expected RT-PCR product (~196 bp) was generated in RT-PCR using pospiviroid- specific primers and their sequences were shown to share strong identities (94%) with Mexican papita viroid (MPVd). Using a new set of primers developed to generate tomato infecting viroids, a full genomic sequence (359 nt) was obtained in isolate Mex8 and confirmed its close relationship to MPVd (93-94%), followed by TPMVd (92%). MPVd was first identified in Mexico on papita (Solanum cardiophyllum) and has only recently been identified to cause a natural infection on greenhouse tomatoes in Canada (Ling and Bledsoe, unpublished). Interestingly, when another set of primers previously designed for Potato spindle tuber viroid and related viroids were used in RT-PCR, a different type of viroid sequence was identified. This second sequence (361 nt) were identified as Tomato chlorotic dwarf viroid (TCDVd) and had a high sequence identity (96-97%) to TCDVd isolates from Japan, North America and Europe. The origin of TCDVd in this greenhouse was not determined, however, TCDVd could potentially be seed-transmitted in tomato. To our knowledge this is the first report of a natural infection of MPVd and TCDVd on commercial greenhouse tomatoes in Mexico.