Abstract
Many Japanese isolates of citrus tristeza virus (CTV) vary in the severity of symptoms which they induce. To study the molecular variability of these isolates, a reverse transcription polymerase chain reaction technique (RT-PCR) was used to amplify part of the CTV genome. PCR products included the 3'-end of the 27K protein gene, most of the 5'-end of the coat protein (CP) gene and the intercistronic region (GAP) between the two genes. Nucleotide sequence analysis of PCR products classified the 13 nucleotide sequences obtained from 12 Japanese isolates of CTV into three groups. Group I contains severe isolates (1215A, 1513A, 1595A-1, HS34, KS3A2), group II mild isolates (BOUQA, M12A, M15A, M27A), and group III severe (S5A2, S5agA) and mild (M23A, 1595A-2) isolates. In the GAP region, a deletion of bases in the Japanese severe CTV isolates may be useful in developing a molecular technique to discriminate CTV isolates. The amino acid residue at position 124 of the coat protein appeared previously to be the most conserved and isolate-specific for mild and severe strains. Among Japanese CTV isolates, however, two mild isolates M15A and M23A had the same residue at position 124 as severe isolates. Based on these results, a greater diversity exists among Japanese CTV isolates than among those in other citrus producing areas.
