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Natural Infection of Canavalia ensiformis with Tobacco mosaic virus in Venezuela

Jack bean (Canavalia ensiformis) is a valuable green manure and cover-crop species. In late summer of 2002, jack bean plants showing severe stunting, leaf mosaic, mottling, distortion, and general yellowing were observed in fields located in Maracay, Aragua State, Venezuela. Sap from symptomatic leaves was used to mechanically inoculate healthy jack bean, and field symptoms were successfully reproduced. Similar inoculations on Nicotiana tabacum var. Sansum resulted in mosaic symptoms and leaf distortion. Electron microscopic examination of leafdip preparations showed filamentous rods resembling those of a tobamovirus. Tobacco mosaic virus (TMV) was specifically identified with TMV-specific polyclonal antibody (PVAS-958, ATTC) in enzyme-linked immunosorbent assay. Sequence analysis of a coat protein gene (CP) fragment amplified using reverse transcription-polymerase chain reaction (RT-PCR) with primers TMV-CP-F and TMV-CP-R (1) from total RNA confirmed the diagnosis. Nucleotide and deduced amino acid sequences of a 450-bp region of the RT-PCR product were 96 to 99% and 98 to 100% identical, respectively, to the TMV CP gene in GenBank Accession Nos. J02415 and X68110. On the basis of foliar symptoms, incidence of TMV in jack bean was more than 50% in this experimental field. The source of infection is not known. Because TMV is reported to be seedborne in many other plant species, testing jack bean seed stocks for TMV infection could have important implications on the future control of the virus. To our knowledge, this is the first report of natural infection of jack bean by a tobamovirus.

Reference: (1) N. J. Spence et al. Eur. J. Plant Pathol. 107:633, 2001.