GENETIC DIVERSITY OF TOMATO LEAF CURL VIRUSES (BEGOMOVIRUS COHENI) INFECTING TOMATO

Abstract

Background: Sequence analyses and phylogenetic comparison indicated that, the five isolates of B. coheni might have evolved by recombination between viruses related to two or more viral ancestors.  The isolates were different from north Indian isolates, with variability even within isolates collected from a geographical location, indicating that, there will be continuous variability in geminiviruses.

Objective: To study the genetic diversity of ToLCD belongs to a group of closely related begomoviruses that emerged in the regions of Tamil Nadu, India, and to identify and determine their molecular variability.

Methods: Infected plant samples of ToLCV were collected from S. lycopersicum plants expressing typical symptoms of leaf curling, stunting, distortion, interveinal yellowing and necrosis of older leaves from tomato growing areas of Salem, Erode, Coimbatore, Madurai and Tirunelveli districts of Tamil Nadu. Totally 11 villages were surveyed randomly during 2010-2012 and the plant samples were immediately frozen in liquid nitrogen and stored at -80°C for further studies.

Results: The ToLCD symptoms varied from place to place and were exhibiting mild to severe leaf curling, reduction in leaf size and shortening of internode, upward curling, stunted growth, reduction in leaf size and puckering. The PCR was performed using ToLCV specific primers and fragment length of ~2.4 kb size obtained in 15 of 19 samples tested to confirm the presence of ToLCV. Based on the above work the ToLCV specific primers were designed and analyzed for further study. The complete nucleotide sequences (~2.7 kb) of selected isolates amplified by PCR were found to be monopartite genome and identified as 2 species of Tomato leaf curl viruses. On the basis of nucleotide similarity (89%) the virus from Tomato leaf curl Karnataka virus-CBE 1 and Tomato leaf curl Karnataka virus-SA1 of Tamil Nadu and virus from Tomato leaf curl Gujarat virus- EDE1, Tomato leaf curl Gujarat virus-TRN1 and Tomato leaf curl Gujarat virus-MDU1 have been identified ToLCKV and ToLCGV. The proposed name is ToLCKV and ToLCGV.

Conclusion: This study is a report that reveals the presence of new strains of geminiviruses infecting tomato plants, which have single genomic component and molecular diversity of Tamil Nadu region. Transcription of this single component produces all gene products required to support a complete cycle of infection and transmission of the virus.