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A New Begomovirus Species Causing Tomato Leaf Curl Disease in Varanasi, India

In November 2001, a leaf curl disease of tomato, manifested by yellowing of leaf lamina, upward leaf curling, leaf distortion, shrinking of leaf surface, and stunted plant growth was observed in tomato-growing areas in the Varanasi and Mirzapur districts of eastern Uttar Pradesh, India, which caused yield losses up to 100%. The causal agent was infective to tomato cv. Punjab Chuhara by whiteflies and grafting. Inoculated plants developed symptoms observed in naturally infected tomatoes. Viral DNA was isolated from artificially inoculated tomato plants using 1% CTAB (2) followed by a concentration of supercoiled DNA by alkaline denaturation (1). A geminivirus was confirmed by polymerase chain reaction using DNA-A degenerate primers (3), and a 550-bp amplified product was obtained from artificially and naturally infected plants. Full-length viral genomes of DNA-A and DNA-B were cloned in plasmid pUC18 at HindIII and XbaI sites, respectively. Partial tandem dimers of the viral clones were infective to Nicotiana benthamiana and tomato cv. Organ Spring through particle bombardment. Infected N. benthamiana plants exhibited downward and upward leaf curling, big veins, leaf puckering with interveinal chlorosis, and stunting. On tomato, symptoms were the same as those seen on naturally infected plants. Cloned DNA also infected Capsicum annuum cv. California Wonder (upward leaf curling and stunting) and tobacco cv. Xanthi (leaf curling and crinkling) but failed to infect Phaseolus vulgaris, okra, cotton, and N. glutinosa. The Varanasi isolate was sap transmissible (0.1 M potassium phosphate buffer, pH 7.0) from the bombarded plants to N. benthamiana and tomato cv. Organ Spring. DNA-A alone infected N. benthamiana (upward leaf curling and big veins) and tomato cv. Organ Spring (mild leaf curl), but symptoms were delayed and milder. Full-length genome sequencing revealed DNA-A (AY190290) contained 2,757 nt and DNA-B (AY190291) contained 2,688 nt. DNA-A of the Varanasi isolate shares 98.4% identity with a DNA-A sequence (AF449999) obtained from a tomato showing leaf curl symptoms from the same region and 97.1% identity with an isolate from Gujarat (900 km from Varanasi). All three sequences represent isolates of the same species, herein called Tomato leaf curl Gujarat virus, based on the priority of submission of the DNA sequence for the Gujarat region (ToLCGV; AF 413671). All isolates noted were obtained from GenBank. However, except for the DNA-A sequence, no other information is available for these ToLCGV isolates. DNA-A of the ToLCGV-Varanasi isolate shares 66.8% identity with Tomato leaf curl New Delhi virus, severe strain (ToLCNdV-Svr) (U15015), and 84.1% with Tomato leaf curl Karnataka virus (U38239). No DNA-B has been reported for these two ToLCGV isolates, and no infectious clone proving the etiology of the disease has been constructed, except for ToLCGV-Varanasi. DNA-B of ToLCGV-Varanasi shares 79.2% homology with ToLCNdV-Svr and 84.1% with ToLCNdV-Luc (X89653). These results suggest that the isolate from Varanasi belongs to ToLCGV, a previously undescribed geminivirus species causing a devastating tomato leaf curl disease in Gujarat and Uttar Pradesh.

References: (1) H. C. Birnboim and J. Doly. Nucleic Acids Res. 7:1513, 1979. (2) K. M. Srivastava et al. J. Virol. Methods 51:297, 1995. (3) S. D. Wyatt and J. K. Brown. Phytopathology 86:1288, 1996.