Unit of Plant Virology, Division of Plant Pathology, Indian Agricultural Research Institute, New Delhi-110012, India.
Abstracts of the papers presented at the International Conference of Indian Virological Society on “Emerging and Re-emerging viral Diseases of the Tropics and Subtropics” at Indian Agricultural Research Institute, New Delhi, India, December 11–14, 2007.
Citrus tristeza virus (CTV), a member of genus Closterovirus, is one of the largest known plant virus predominantly transmitted by brown citrus aphid, Toxoptera citricida. CTV is the causal agent of the most destructive disease causing decline of several millions of citrus trees worldwide. Present a large number of biological and genetic variants of CTV has been reported. The citrus growing areas in India are distributed into four geographical zones namely Northwest zone, Northeast zone, Central zone and Southern zone. Diseases caused CTV have been reported from all the citrus growing region of India but CTV isolates from all the citrus growing zones are not well characterized. In the present study CTV isolates of Bangalore region of Southern zone were characterized genetically and variability at genetic level was compared with other Indian and exotic CTV. Infected samples from Bangalore region were collected, confirmed by ELISA and maintained in planta Kagzi lime through bud-wood grafting. Molecular profiling was generated amplifying the CTV genes using 10 sets of primers, which suggested that Bangalore isolates were similar with each other, but different from Darjeeling CTV isolates Kpg1 and Kpg2. The coat protein (CP) gene (672 bp) and a fragment (404 bp) of 5’ ORF1a variable region were amplified using specific primers K543F and K544R, and CN488F and CN491R, respectively. The amplicons were cloned and sequenced. Nucleotide sequences of CP and 5’ ORF1a variable region genes were analyzed and compared with other Indian and exotic CTV and also phylogenetic tree was designed. CP gene sequences of Bangalore CTV isolates shared 92–99% sequence identity among them and phylogenetic trees based on CP gene sequences showed that they formed two distant groups, CTV-B in one group along with Kpg1 (99% identity) and BNG1and BNG-2 in another group along with Darjeeling isolate Kpg3 (97–99% identity). Further, sequence analysis of 5’ ORF1a variable region gene showed that Bangalore isolates shared 84–99% nucleotide identity among them and based on phylogenetic tree they fell in two distant groups, one group was found to be similar to Darjeeling isolate CTK14 (97% identity) and another is similar to Kpg3 (95–99% identity). Some Bangalore isolates were found to be similar genetically with Israeli CTV isolate VT.
