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Occurrence of Impatiens necrotic spot virus and Tomato spotted wilt virus on Potatoes in Iran

There have been an increasing number of records of the natural infection of various crops and ornamentals in Iran with Impatiens necrotic spot virus (INSV), Tomato spotted wilt virus (TSWV), and Tomato yellow fruit ring virus (TYFRV), a recently proposed species in the genus Topovirus (3). TYFRV, originally believed to be TSWV and named as such, has been previously reported to occur in Iranian potato fields (2). During the growing seasons of 2004 to 2006, surveys were conducted in potato fields in different potato-producing (Solanum tuberosum) provinces of Iran (Ardabil, Azarbayejan-e-sharqi, Chaharmahal-va-bakhtiyari, Esfahan, Hamedan, Kerman, Khorasan, Khuzestan, Lorestan, Tehran, Qazvin, and Zanjan) to detect the presence of Tospovirus spp. infecting this crop, including Groundnut ringspot virus (GRSV), INSV, Iris yellow spot virus (IYSV), Tomato chlorotic spot virus (TCSV), TSWV, TYFRV, and Watermelon silver mottle virus (WSMoV). Overall, 186 fields were surveyed, and 2,823 potato leaf samples from plants showing tospovirus-like symptoms of chlorotic or necrotic spots, chlorosis, and necrosis were collected before or through the flowering stage, approximately 50 to 90 days after planting. Each leaf sample was tested by double-antibody sandwich (DAS)-ELISA using specific antisera (Bioreba, Reinach, Switzerland; Loewe, Sauerlach, Germany; DSMZ, Braunschweig, Germany) for the presence of the aforementioned tospoviruses. TYFRV, TSWV, and INSV were found in 24.0, 4.1, and 0.4% of the samples collected from 133, 51, and 7 fields surveyed, respectively. None of the samples had a positive reaction in ELISA to GRSV, IYSV, TCSV, and WSMoV. To confirm this testing, a number of the leaf samples that were found to be positive for INSV, TSWV, and TYFRV in ELISA tests were mechanically inoculated on Petunia × hybrid and Nicotiana benthamiana; the inoculated plants showed typical necrotic local lesions of tospoviruses and chlorotic or necrotic spots followed by systemic infection, respectively; their infection was subsequently confirmed by ELISA. The samples also were tested by reverse transcription-PCR technique using previously described specific primers (1,4). The PCR reaction resulted in the specific amplification of a 0.59-, 0.71-, and 0.67-kb (or 1.2-kb) fragment of INSV, TSWV, and TYFRV RNAs, respectively. This study showed that tospoviruses, especially TYFRV, are widespread in Iranian potato fields. It is hoped that the results may help us to improve a seed potato certification program in the future. To our knowledge, this is the first report of INSV and TSWV from potatoes in Iran.

References: (1) A. R. Golnaraghi et al. Plant Dis. 92:1280, 2008. (2) R. Pourrahim et al. Plant Dis. 84:442, 2001. (3) S. Winter et al. Plant Pathol. 55:287, 2006. (4) H. Uga and S. Tsuda. Phytopathology 95:166, 2005.