First Report of Tobacco streak virus Infecting Guizotia abyssinica from India

Guizotia abyssinica (L.f.) Cass. (niger), an important oil seed crop grown in India, is used in foods, paints, soaps, and as an illuminant. During a survey conducted in 2004 to monitor Tobacco streak virus (TSV) in Helianthus annuus L. (sunflower) and Arachis hypogaea L. (groundnut), typical symptoms of leaf and petiole necrosis were observed in niger plants from Karnataka State, India. The field-collected samples reacted with TSV-specific polyclonal antiserum in direct antigen coated (DAC)-ELISA. Indicator host species were mechanically inoculated with extracts from symptomatic leaves and grown under greenhouse conditions. The inoculations resulted in local necrotic lesions on Vigna unguiculata cv. C-152 (cowpea), Gomphrena globosa, and Nicotiana tabacum cv. Xanthi (tobacco) at 3 to 4 days postinoculation (dpi) and systemic mosaic mottling on sunflower and G. globosa at 7 to 9 dpi. To identify the virus at the molecular level, total RNA was isolated (RNeasy kit, Qiagen Inc., Chatsworth, CA) from the virus-inoculated cowpea leaf and used for reverse transcription-PCR using TSV CP (coat protein) specific primers (2). The resulting ~720-bp amplicon corresponding to the CP gene of TSV was cloned into pGem-T vector (Promega, Madison, WI) and sequenced. The resulting sequence of the TSV-niger isolate (TSV-NG) comprised 717 nucleotides encoding 238 amino acid residues of the viral coat protein (GenBank Accession No. DQ864458). Comparison of the sequence with those of other TSV CP gene indicated 98.5 to 99.3% nucleotide and 97.9 to 99.6% amino acid sequence identity with TSV isolates from India (1,2; GenBank Accession Nos. AF505073, AY061930, AY061929, AF515823, AF515824, and AF515825). The sequence of TSV-NG had 89.5 and 80.0% amino acid identity with TSV-WC, type strain from the United States (GenBank Accession No. X00435) and TSV-BR, isolate from Brazil (GenBank Accession No. AY354406), respectively. On the basis of symptoms, transmission, and serological and molecular data, the causal agent of necrosis in niger was identified as a strain of TSV widely prevalent in other oil seed and vegetable crops in India. The new report of Tobacco streak virus infecting niger from India, indicated the expansion of host range among oil seed crops. References: (1) A. I. Bhat et al. Indian J Biotechnol. 1:350, 2002. (2) K. S. Ravi et al. Plant Pathol. 50:800, 2001.