Tomato yellow leaf curl virus (TYLCV) and Tomato spotted wilt virus (TSWV) are prevalent in field-grown tomato (Solanum lycopersicum) production in Georgia. Typical TYLCV symptoms were observed during varietal trials in fall 2009 and 2010 to screen genotypes against TYLCV at the Coastal Plain Experiment Station, Tifton, GA. However, foliar symptoms atypical of TYLCV including interveinal chlorosis, purpling, brittleness, and mottling on upper and middle leaves and bronzing and intense interveinal chlorosis on lower leaves were also observed. Heavy whitefly (Bemisia tabaci (Gennadius), B biotype) infestation was also observed on all tomato genotypes. Preliminary tests (PCR and nucleic acid hybridization) in fall 2009 indicated the presence of TYLCV, TSWV, Cucumber mosaic virus, and Tomato chlorosis virus (ToCV); all with the exception of ToCV have been reported in Georgia. Sixteen additional symptomatic leaf samples were randomly collected in fall 2010 and the preliminary results from 2009 were used to guide testing. DNA and RNA were individually extracted using commercially available kits and used for PCR testing for ToCV, TYLCV, and TSWV. Reverse transcription (RT)-PCR with ToCV CP gene specific primers (4) produced approximately 750-bp amplicons from nine of the 16 leaf samples. Four of the nine CP gene amplicons were purified and directly sequenced in both directions. The sequences were 99.4 to 100.0% identical with each other (GenBank Accession Nos. HQ879840 to HQ879843). They were 99.3 to 99.5%, 97.2 to 97.5%, and 98.6 to 98.9% identical to ToCV CP sequences from Florida (Accession No. AY903448), Spain (Accession No. DQ136146), and Greece (Accession No. EU284744), respectively. The presence of ToCV was confirmed by amplifying a portion of the HSP70h gene using the primers HSP-1F and HSP-1R (1). RT-PCR produced approximately 900-bp amplicons in the same nine samples. Four HSP70h gene amplicons were purified and directly sequenced in both directions. The sequences were 99.4 to 99.7% identical to each other (Accession Nos. HQ879844 to HQ879847). They were 99.2 to 99.5%, 98.0 to 98.4%, and 98.9 to 99.3% identical to HSP70h sequences from Florida (Accession No. AY903448), Spain (Accession No. DQ136146), and Greece (Accession No. EU284744), respectively. TYLCV was also detected in all 16 samples by PCR using degenerate begomovirus primers PAL1v 1978 and PARIc 496 (3) followed by sequencing. TSWV was also detected in two of the ToCV-infected samples by RT-PCR with TSWV N gene specific primers (2) followed by sequencing. To our knowledge, this is the first report of the natural occurrence of ToCV in Georgia. Further studies are required to quantify the yield losses from ToCV alone and synergistic interactions between ToCV in combination with TSWV and/or TYLCV in tomato production in Georgia.
References: (1) T. Hirota et al. J. Gen. Plant Pathol. 76:168, 2010. (2) R. K. Jain et al. Plant Dis. 82:900, 1998. (3) M. R. Rojas et al. Plant Dis. 77:340, 1993. (4) L. Segev et al. Plant Dis. 88:1160, 2004.
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