Submitted to: Conference of International Organization of Citrus Virologists
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/11/2001
Publication Date: 2/1/2002
Citation: Hilf, M., Garnsey, S.M. 2002. A Broad Integrated Picture of CTV in Florida: A synthesis of Historical and Contemporary Field, Serological, and Genetic Data. Proceedings of the 15th Conference of the International Organization of Citrus Virologists, 13-20. Interpretive Summary: This paper describes the summation of biological, serological and molecular analysis of a collection of citrus tristeza virus (CTV) isolates collected in Florida over a nearly 45 year period. The data show that the population of virus in commercial citrus trees has been stable for this period. This indicates that genetic tests developed that discriminate between Florida CTV and CTV from other parts of the world could be effectively used by state regulatory agencies to screen and protect certified Florida citrus budwood trees against exotic and potentially damaging CTV isolates. This is because we now have a much better understanding of CTV populations in Florida due to this study.
Technical Abstract: The decline of trees on sour orange rootstock is the only commercially important disease currently caused by citrus tristeza virus (CTV) in Florida. Virus isolates from commercial citrus plantings in Florida have previously been characterized biologically as mild and severe. Virus induced stem-pitting is not a commercially important disease in Florida. Discrimination of severe and mild isolates has been accomplished previously by biological indexing and by the monoclonal antibody MC13, which does not react to Florida mild isolates. The Florida T30 and T36 isolates are the type isolates for the mild and severe groups respectively, and both genomes have been fully sequenced. We developed a PCR-based assay to characterize CTV isolates by amplification of sequence specific molecular markers using primers derived from the nucleotide sequence of the VT, T3, T30 and T36 isolates. The pattern of amplified markers is used to assign to a CTV isolate a specific genotype. When we applied this marker analysis to over 300 CTV accessions from Florida, the T30 and T36 genotypes were the primary genotypes in commercial citrus in Florida. Biological indexing of select isolates supported the association of the T36 genotype with induction of a graft incompatibility on sour orange rootstock. The widespread distribution of two predominant genotypes may reflect the sources of CTV germplasm that have been introduced historically and subsequently spread via propagation and aphid vectors. The limited genetic variability of CTV currently present in Florida may facilitate the use of genetically based assays to regulate future ingress of other CTV genotypes into Florida citrus budwood.