Division of Plant Pathology, Indian Institute of Horticultural Research, Hessaraghatta Lake PO, Bangalore-560089.
Okra (Abelmoscus esculentus (L) Moench) is an important vegetable crop of India and other sub-tropical and tropical countries. Survey conducted in Andhra Pradesh, Haryana Karnataka, Maharashtra, and Tamil Nadu states during 2004–05 in different okra growing areas has indicated incidence of fruit distortion mosaic disease caused by Tobacco streak virus (TSV). The incidence of such disease varied from 7.5 to 82.5% indifferent places. The disease is characterized by chlorotic spots, chlorotic leaf blotches, distortion of leaves, chlorotic streaking, distortion of fruits, and may cause severe yield losses of up to 63%. Mechanical transmission of the causal agent reproduced these symptoms on okra, and also induced symptoms on Chenopodium amaranticolor, black gram, cotton, cowpea, peanut, and sunflower. - Electron microscopic observation of leaf dip preparations from field samples and partially purified virus preparations revealed the presence of isometric virus particles measuring 25 to 30 nm in diameter. The seed collected from infected plants did not give positive reaction in ELISA. However, the virus was detected in various parts of infected plant such as leaf, calyx, corolla, pollen of flower, fruit skin, and fruit axis. The virus was not present in seed and gynaecium. In RT-PCR, using oligonucleotide primers designed to amplify the entire coat protein region of TSV, an approximately 800 bp DNA fragment was obtained from both purified virus and okra displaying fruit distortion mosaic disease (OFDM) but not from healthy okra. Phylogenetic analysis of CP gene has indicated that this isolate is 98–99% similar to other TSV isolates from India but has 88%similarity with USA isolate.
