Two Distinct Isolates of Tomato yellow leaf curl virus Threaten Tomato Production in Arizona and Sonora, Mexico

Severe yellow leaf curl and plant stunting symptoms were observed in tomato plants from two home gardens in central Arizona (Phoenix area) and a tomato field in Sonora, Mexico during the fall of 2006. Disease symptoms were reminiscent of those reported in Florida during 1994 (4) and more recently in tomato fields in the Pacific Coast state of Sinaloa, Mexico found to be infected with the exotic Tomato yellow leaf curl virus (TYLCV) (2). Total DNA was extracted from two symptomatic tomato plants from Arizona and Sonora and used as a template in PCR. PCR products of the core region of the begomovirus coat protein gene (Cp) were cloned (n = 3) and the DNA sequence was determined. BLAST analysis of the 579 bases with sequences available in the NCBI GenBank database indicated the closest match was to an isolate of the monopartite begomovirus TYLCV from Israel, which was known to have been introduced into the Caribbean region, including Puerto Rico, the southeastern United States, and Mexico from 1990 to 1996 (1,4). The full-length TYLCV genome (approximately 2,800 bases) was amplified for a field isolate from each location by rolling circle amplification (RCA) using TempliPhi (Amersham Biosciences, Piscataway, NJ). RCA products were cloned into the plasmid vector pGEM7 (Promega, Madison, WI) that had been previously digested with SacI endonuclease. The complete TYLCV genome sequence was determined for six clones from each RCA product. Nucleotide analysis indicated that the complete TYLCV genome sequences from Sonora and Arizona, respectively, shared 97.6 and 97.7% nt identity. The comparative sequence analysis indicated that TYLCV-Sonora (TYLCV-Son) (GenBank Accession No. EF210555) was 99.1% nt identical to TYLCV reported recently from Culiacan, Mexico (GenBank Accession No. DQ631892). In contrast, TYLCV-AZ (GenBank Accession No. EF210554) shared 99.3% identity with an isolate from Texas, TYLCV-TX (GenBank Accession No. EF110890) (3). Interestingly, the TX and AZ TYLCV isolates contained a unique 29-nt deletion in the intergenic region (IR) between the TATA-box and the nonanucleotide, initiating at nt coordinate 2696. Except for the deletion in the IR region of the AZ and TX isolates, these viruses shared 97.6 to 99.1% nt identity to other TYLCV isolates reported in the Western Hemisphere. The genome sequence for TYLCV-Son shares high nt identity with TYLCV isolates identified in the Yucatan Peninsula and Pacific Coast of Mexico (2), the Caribbean region, and the southeastern United States, suggesting that a single TYLCV species was introduced and has spread throughout North America and the Caribbean (4). The absence of other TYLCV isolates in the Western Hemisphere with the novel 29-nt deletion noted for the TX and AZ isolates suggests that the latter two isolates originated from the same U.S. source. In Mexico, TYLCV was first introduced in the east coast and Yucatan region approximately in 1996. From there, this isolate has spread to the western part of the country (Sinaloa and Sonora) from 2004 to 2006 (2). Similarly, in the United States, TYLCV was introduced and spread in the eastern U.S. states beginning in 1994 (4), where it had been confined until it was discovered in Texas (3) and now Arizona during 2006. References: (1) J. Bird et al. Plant Dis. 85:1028, 2001. (2) J. K. Brown and A. M. Idris. Plant Dis. 90:1360, 2006. (3) T. Isakeit et al. Plant Dis. 91:466, 2007. (4) J. E. Polston et al. Plant Dis. 78:831, 1994.