Page Banner

United States Department of Agriculture

Agricultural Research Service

Research Project: CHARACTERIZATION & EPIDEMIOLOGY OF CITRUS TRISTEZA VIRUS & OTHER INVASIVE & EMERGING GRAFT-TRANSMISSIBLE DISEASES OF CITRUS IN CALIFORNIA

Location: Crop Diseases, Pests and Genetics

Title: Assessment of the Citrus tristeza virus isolates detected in spring 2007 at the Lindcove Research and Extension Center, Exeter, California

Authors
item Yokomi, Raymond
item Polek,, Marylou - CCTEA TULARE
item Grafton-Cardwell,, Beth - UC RIVERSIDE
item Vidalakis,, Georgios - UC RIVERSIDE
item O'Connell,, Neil - UC, COOP EXTENSION
item Saponari,, Maria - ISTITUTO DI VIROL. VEG

Submitted to: International Organization of Citrus Virologists Proceedings
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 12, 2009
Publication Date: May 14, 2011
Citation: Yokomi, R.K., Polek,, M., Grafton-Cardwell,, B., Vidalakis,, G., O'Connell,, N., Saponari,, M. 2011. Assessment of the Citrus tristeza virus isolates detected in spring 2007 at the Lindcove Research and Extension Center, Exeter, California. International Organization of Citrus Virologists Proceedings. p. 28-35.

Interpretive Summary: The Univ. California’s Citrus Clonal Protection Program (CCPP) maintains many registered virus-free budwood source trees in the field at the Lindcove Research and Extension Center (LREC) near Exeter, CA. Adjacent to the CCPP, LREC has 51 ha planted to citrus for research purposes. In spring 2007, 50 trees at the LREC were found infected with citrus tristeza virus (CTV). This is an unprecedented high rate, and a serious threat to LREC and the CCPP, as only 0 to 3 new infections are typically found each year. The purpose of this research was to assess genetic diversity and aphid transmissibility of CTV isolates associated with increased incidence at the LREC. Aphids transmitted the virus from 5 of the 9 source trees with an overall efficiency of 12.5%. A multiple locus genetic marker analysis showed all isolates had a T30 genotype consistent with mild strains of CTV. A hierarchical survey in a ½ mile radius of the LREC estimated 1,296 infected trees were in this area. Approximately 200 CTV-infected samples from the surveyed area were analyzed and found to have the same multiple molecular marker profile as the LREC isolates. However, a phylogenetic analysis of cloned coat protein (CP) gene sequences indicated that an isolate from citron was clearly distinct from other LREC isolates and clustered in a clade with isolates reactive to MCA13, a strain-discriminating monoclonal antibody. Single strand conformational polymorphism (SSCP) analysis of the CP gene also identified five samples from the ½ mile survey with the same unique CP SSCP pattern as the LREC citron isolate. These data show that the LREC CTV isolates are readily aphid transmissible and have a genotype associated with a mild CTV strain. However, some genetic diversity was found and biological characterization studies are underway to examine the virulence of the CTV citron isolate. These results are being used to support establishment of a CTV eradication program around the LREC to help maintain the virus-free citrus trees in the CCPP.

Technical Abstract: Citrus tristeza virus was detected in at least 50 trees at the 71 ha Lindcove Research and Extension Center (LREC) near Exeter, Calif. in spring 2007. The purpose of this research was to assess genetic diversity and aphid transmissibility of these isolates. Nine representative trees were sampled on May 21, 2007, prior to removal. Examination was performed by ELISA, RT-PCR, multiple molecular marker assay, coat protein (CP) gene analysis and vector transmission. Aphids transmitted CTV from 5 of the 9 source trees with an overall efficiency of 12.5%. All nine isolates had a T30 genotype. A hierarchical bulk survey (HS) of citrus in a ½ mile radius of the LREC estimated 1,296 trees were infected with CTV with an overall incidence of 1.2%. CTV positive HS samples (201) were examined and identified as genotype T30, a mild strain of CTV. Phylogenetic analysis of the CP gene region showed a LREC citron isolate was distinct from the other mild isolates and clustered with CCTEA 114, 108 and 115 in a clade that included genotype T36. Furthermore, these isolates reacted with MCA13, a strain discriminating monoclonal antibody. SSCP also identified five samples from the HS survey that contained the same CP pattern as the LREC citron isolate. These data show that the LREC CTV isolates are readily aphid transmissible and most have a genotype associated with mild a CTV strain. However, some genetic diversity was found and biological characterization studies are underway to examine the virulence of the CTV citron isolate. These results are being used to support establishment of a CTV eradication program around the LREC to help maintain the virus-free citrus trees in the CCPP.

Last Modified: 4/17/2014
Footer Content Back to Top of Page