Submitted to: Virus Genes
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/26/2009
Publication Date: 10/16/2009
Citation: Melzer, M.J., Borth, W., Sether, D., Ferreira, S., Gonsalves, D., Hu, J.S. 2009. Genetic diversity and evidence for recent modular recombination in Hawaiian Citrus tristeza virus. Virus Genes. 40:111-118. Interpretive Summary: Citrus tristeza virus (CTV) is the most economically and widespread virus affecting citrus world wide. Typically, trees are infected with a number of strains of CTV which can be detected by differences in their nucleotide sequences. The biological implication that these strains have on the severity or mildness of the disease is still not clear. Hawaii is an ideal place to study strain variation of CTV because apparently numerous strains have been introduced over the years. This study examined two strains of CTV, HA18-9 and HA16-5, that are apparently unique to Hawaii as judged by their sequences. The data suggest that HA16-5 might have arose through recombination between parts of HA18-9 and an unknown CTV strain. The revelations in this study may provide insights on the reasons why many strains of CTV exist in an infected tree. Understanding this phenomena could help provide more rationale management approaches for control this very severe disease.
Technical Abstract: The Hawaiian Islands are home to a widespread and diverse population of Citrus tristeza virus (CTV), an economically important pathogen of citrus. In this study we quantified the genetic diversity of two CTV genes and determined the complete genomic sequence for two strains of Hawaiian CTV. The nucleotide diversity was estimated to be 0.0565±0.0022 for the CP gene (n=137) and 0.0822±0.0033 for the p23 gene (n=30). The genome size and organization of CTV strains HA18-9 and HA16-5 were similar to other fully-sequenced strains of CTV. The 3’-terminal halves of their genomes were nearly identical (98.5% nucleotide identity), whereas the 5’-terminal halves were more distantly related (72.3% nucleotide identity), suggesting a possible recombination event. Closer examination of strain HA16-5 indicated that it arose through recent recombination between the movement module of an HA18-9 genotype, and the replication module of an undescribed CTV genotype.