GENETIC STRUCTURE OF CITRUS TRISTEZA VIRUS IN HUNAN PROVINCE (P.R. CHINA)

The genetic structure of the Citrus tristeza virus (CTV) population in the Hunan Province, China, was studied by capillary electrophoresis-single strand conformation polymorphism (CE-SSCP), multiple molecular markers (MMM), and bioindexing. A total of 17 samples collected in Yizhang and Yong Xing counties were tested by tissue print-ELISA, and 10 were found CTV infected. CE-SSCP analysis showed different profiles some of them indicating composite patterns. MMM analysis revealed the presence of the VT and T3 genotypes, either individually or in combination. One more isolate from Chenzou (HU-PSTS) showing the most complex CE-SSCP profile and a T36 + VT + T30 genotype was further investigated by graft inoculation on indicator plants and phylogenetic analysis of the p25 gene. Bioindexing revealed a very severe seedling yellows reaction and an unusual stem pitting on sour orange. Three p25 clones obtained from this isolate, showed different CE-SSCP profiles and were phylogenetically close to recombinant Hawaiian and Indian strains.