Division of Molecular Virology, Mahyco Research Center, Dawalwadi, Jalna.
Abstracts of Research Papers Presented during the National Symposium of Indian Virological Society at Unit of Plant Virology, Division of Plant Pathology, Indian Agricultural Research Institute, New Delhi-110 012, October 14–1.
Okra yellow vein mosaic virus (OYVMV) is a monopartite circular single stranded DNA virus transmitted by whitefly Bemisia tabaci and causing devastating disease in Okra. In recent years, unusual occurrence of yellow vein mosaic (YVM) was commonly encountered and the incidence varied from 5–100 per cent. In order to assess the distribution and genetic variability in the virus, a countrywide survey and collection of virus isolates was undertaken from 19992004. Over 150 YVM isolates were collected from different okra growing regions of the country for biological and molecular characterization. Nearly one fourth of DNA-A component from the representative isolates were PCR amplified, cloned and sequenced. Sequence analysis showed high degree of variability among YVM isolates and observed ten different species. Around 80 per cent of the isolates collected from different regions were aligned into a common cluster, which represents a most predominant species. The virus isolates collected from Gujarat are highly distinct and aligned into two distinct clusters based on the symptoms and nucleotide sequence. The isolates with enations like symptoms were identical (95.5%) with the CLCuGV reported from Egypt and another cluster from the same region were produced with typical YVM symptoms. Interestingly a group of isolates collected from West Bengal, Orissa and parts of Maharashtra were showed with stem bending symptoms which as been identified as another distinct species. Rest of the OYVMV species identified in okra are identical to common tomato leaf curl virus sequences, which are location specific from different parts of the country. Some YVM isolates collected from West Bengal are having more than 89.0% sequence identity with the yellow motle type tomato leaf curl virus isoaltes. In general, mixed infection of more than one species and/or strains of the YVM as been observed frequently. Recombination within the pre-existing geminiviruses in different crops/weeds may be a reson for emerging new strains/species. In addition to complex sequence variability and diversity, association of DNA-beta molecules with DNA-A component was frequently encountered in the country. The biological and functional role of DNA-beta along with the DNA-A molecule in symptom development, severity and virus movement is yet to be ascertained with the geminivirus infections.
