Tomato yellow leaf curl virus in Tomato in Texas, Originating from Transplant Facilities

Tomato yellow leaf curl virus (TYLCV), a monopartite virus in the genus Begomovirus (family, Geminiviridae) from the Middle East, is one of the most damaging whitefly-transmitted viruses of tomato (Lycopersicon esculentum) worldwide. TYLCV was first identified in the United States in 1997 in Florida (4), and most recently, in the Pacific Coast states of Mexico where fresh market tomatoes are grown for the U.S. market (1). During September 2006, tomatoes grown from transplants in Waller County, TX exhibited shortened internodes, stunting and puckering of leaflets, green vein banding, and diffuse chlorosis. The disease incidence in two fields (4 ha total) was 95% and yield was substantially reduced. Many of the transplants were symptomatic at planting. The transplants originated from two facilities in Hidalgo County, TX. Both facilities had experienced heavy infestations of the whitefly, Bemisia tabaci (Genn.), during transplant production. At the same time, transplants produced in Uvalde and Bexar counties, TX, where whitefly infestations were also prevalent, had similar virus symptoms. Total DNA was extracted from the leaves of symptomatic tomato plants from 10 samples from these four counties and amplified by PCR (2). DNA samples from Waller, Hidalgo, and Uvalde counties were cloned, and a partial fragment of the viral coat protein gene (core Cp) was sequenced. BLAST analysis of the core Cp sequences of each sample confirmed the presence of TYLCV. No other begomovirus was detected, and all attempts to amplify a bipartite begomovirus by PCR using degenerate DNA-B specific primers (3) were unsuccessful. The full-length TYLCV DNA was amplified from three samples using the rolling circle amplification method as described (1), cloned, and the sequences were determined. The three sequences shared 99.6 to 100% nt identity and so only one sequence was deposited in the NCBI GenBank database (Accession No. EF110890) (1). Analysis of the complete genome nucleotide sequence corroborated TYLCV identity predicted by core Cp analysis that was 98.1% identical with TYLCV from Egypt (GenBank Accession No. AY594174) and Spain (GenBank Accession No. AJ489258), 97.6% with TYLCV from Mexico (GenBank Accession No. DQ631892), and 96.5% with TYLCV-Is (GenBank Accession No. X15656). Additionally, a Southern blot with TYLCV as the probe detected replicating (double-stranded) TYLCV DNA in all samples consisting of three plants from Uvalde County and 21 plants from Bexar County. To our knowledge, this is the first report of TYLCV in Texas that occurred in two transplant production areas approximately 400 km apart. Transplants produced in Uvalde and Bexar counties were planted there, while Hidalgo County transplants were shipped outside of the usual range of the whitefly. Hidalgo County has a subtropical climate, which can allow overwintering of TYLCV and the whitefly vector, allowing the establishment and spread of this virus in the future. References: (1) J. K. Brown and A. M. Idris. Plant Dis. 90:1360, 2006. (2) J. K. Brown et al. Arch. Virol. 146:1581, 2001. (3) A. M. Idris and J. K. Brown. Phytopathology 88:648, 1998. (4) J. E. Polston et al. Plant Dis. 83:984, 1999.