|Yokomi, Raymond - Ray|
|HAJERI, SUBHAS - Central California Tristeza Eradication Agency|
Submitted to: International Organization of Citrus Virologists Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 2/7/2019
Publication Date: N/A
Technical Abstract: In California, reactivity of Citrus tristeza virus (CTV) isolates to CTV monoclonal antibody MCA13 is rare. A positive test suggests that the isolate may be exotic, potentially severe and, hence, subject to regulatory action. Full-length sequencing of several California MCA13-reactive isolates revealed that they grouped in three different CTV genotypes: VT, RB, and S1 (1,2). Greenhouse virus indexing showed that the VT strains were virulent but the RB and S1 strains were mild. Phylograms showed the Dekopon isolate was associated with the CTV Western VT group. RB strains were associated with two CTV RB subgroups: Group 1 (similar to New Zealand isolates); and Group 2 (similar to Asian-Pacific isolates). Two isolates formed a new genotype named S1. Isolates from these genotypes were present alone or in combination with other genotypes. Sequence analysis provided strong evidence that the RB and S1 strains originated as recombinants. RT-qPCR primers and probes were designed and validated to identify and differentiate these strains. CTV accessions maintained in plants in a quarantine greenhouse tested by these new genetic markers revealed that some of MCA13 reactive isolates have been present in California since before 1968. This research provided important data on genetic diversity of CTV and suggested that CTV testing by MCA13 should be supplemented with strain-specific RT-qPCR markers to more accurately determine potential virulence.