Molecular Virology Division, Mahyco Research Center, 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.
Geminiviruses are one of the fastest emerging and devastating pathogens of vegetables and cotton. In recent years, unusual occurrence of geminiviral infections was commonly encountered in tomato, okra, cotton and cucurbits. In order to assess the distribution and genetic diversity of the virus, a countrywide survey and collection of virus isolates was undertaken for biological and molecular characterization. Nearly 700 bp region of DNA-A molecules were analyzed using PCR based cloning and sequencing. Over eighty ToLCV isolates analyzed were grouped into twelve major phylogenetic clusters or species with the phenotypic symptoms of leaf curl and yellow mottle types. The yellow mottle isolates collected from Maharashtra and Northern India are unique by its symptoms & virus transmission and aligned into an independent group or species. There is a high degree of nucleotide sequence identity between the yellow mottle virus isolates in tomato and cucurbits. In okra, phylogenetic analysis of over 100 OYVMV isolates collected from different locations was clustered into ten new species with varied symptoms (yellow vein, vein thickening, enations and stem bending). It has been observed that some of the ToLCV sequences were also found in okra isolates. Similarly, CLCuV isolates collected from Punjab and Haryana were clustered into six different species and majority of the sequences were related to OYVMV and CLCuV-Pak. Based on the nucleotide comparisons and phylogenetic analysis of tomato, okra and cotton infecting geminiviruses, revealed a number of undescribed species of begomoviruses in India. Analysis also indicated the existence of a high degree of genetic diversity among virus isolates collected from different geographic regions. The study revealed a strong evidence of recombination among virus sequences. The newly emerging geminvirus species or strains are known to be better adapted to the new host and environment and becomes more virulent and severe. Mixed infections of more than one strain or species were observed among the virus isolates.
In addition to complex sequence diversity among the virus isolates, association of DNA-beta molecules with the respective DNA-A component in tomato, okra and cotton were frequently encountered. 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.
