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First Report of Tomato chlorosis virus in Potato in Brazil

Potato plants (Solanum tuberosum cv. Ágata) exhibiting symptoms of leaf roll and interveinal chlorosis, especially on older leaves, were found in a commercial crop in the County of Cristalina, State of Goiás, Brazil in June 2011. The crop was severely infested by whitefly Bemisia tabaci biotype B. Four potato tubers from symptomatic plants were indexed for the presence of the following viruses: Tomato chlorosis virus (ToCV), Potato leaf roll virus (PLRV), Tomato severe rugose virus (ToSRV), and Potato virus Y (PVY). Total RNA was extracted separately from each tuber and used for reverse transcription (RT)-PCR using the HS-11/HS-12 primer pair, which amplifies a fragment of 587 bp from the highly conserved region of the heat shock protein (HSP-70) homolog gene reported for ToCV. The RT-PCR product was subsequently tested by nested-PCR for detection of ToCV with specific primers ToC-5/ToC-6 (2). Amplicons of 463 bp, amplified from total RNA separately extracted from three tubers, were purified and directly sequenced. Comparisons among the three consensus sequences of 448 bp (GenBank Accession Nos. JQ288896, JQ288897, and JQ288898) revealed respectively, 98, 100, and 100% identity with the reported sequence of a tomato isolate of ToCV from Brazil (GenBank Accession No. EU868927) (1). For ToSRV detection, total DNA was extracted from two tubers and a fragment of approximately 820 bp was amplified by PCR with specific primers (3). PLRV and PVY were indexed in two and three tubers, respectively, by double-antibody sandwich-ELISA (SASA, Edinburg, Scotland). Virus-free B. tabaci biotype B were separately transferred to potato and tomato leaves infected with ToCV for an acquisition access period of 24 h. Groups of 30 viruliferous whitefly were transferred to four, young, sprout-grown potato plants cv. Ágata (two plants per virus isolate) for 24-h inoculation access period. After 37 days of inoculation, one plant inoculated with the potato and tomato isolates of ToCV, respectively exhibited symptoms of leaf roll and interveinal chlorosis on order leaves, which were similar to that induced by PLRV. Experimental infection of potato plants with ToCV, which induced leaf roll symptoms resembling PLRV infection, was reported in the United States by Wisler et al. (4). The potato isolate of ToCV was also transmitted by B. tabaci to one of two inoculated tomato plants. The presence of ToCV in all inoculated plants was detected by nested-RT-PCR as described above. To our knowledge, this is the first report on detection of ToCV in field potato plants in the world. Considering that ToCV occurs in innumerous countries around the world, it is transmitted by a cosmopolitan insect, and it induces symptoms similar to PLRV, this finding triggers an alert to field dependent seed-potato multiplication, virus inspector, and certification system.

References: (1) J. C. Barbosa et al. Plant Dis. 92:1709, 2008. (2) C. I. Dovas et al. Plant Dis. 86:1345, 2002. (3) F. R. Fernandes et al. Trop. Plant Pathol. 35:43, 2010. (4) G. C. Wisler et al. Plant Dis. 82:270, 1998.