CHARACTERIZATION, EPIDEMIOLOGY AND MANAGEMENT STRATEGIES OF CITRUS TRISTEZA VIRUS AND SPIROPLASMA CITRI ON CITRUS IN CALIFORNIA
Location: Crop Diseases, Pests and Genetics
Title: Molecular diversity of Citrus tristeza virus (CTV) strains collected over the past 50 years and maintained in CTV collections in California
Submitted to: International Citrus Congress Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: August 23, 2012
Publication Date: November 18, 2012
Citation: Wang, J., Bozan, O., Kwon, S., Rucker, T., Thomas, C., Yokomi, R.K., Lee, R.F., Folimonova, S., Vidalakis, G. 2012. Molecular diversity of Citrus tristeza virus (CTV) strains collected over the past 50 years and maintained in CTV collections in California. International Citrus Congress Proceedings. S14P06, p.240.
Tristeza, caused by Citrus tristeza virus (CTV), is a serious citrus disease worldwide. Because severe strains of CTV reduce fruit production and quality, CTV has been eliminated from citrus germplasm sources by a certification program. CTV is also a regulated pathogen in quarantine zones and infected trees have been removed. Rapid detection and inoculum removal has resulted in limited genetic diversity of CTV in Central California. The majority of strains have a T30-like genotype. T30 genotype strains typically cause no damage on citrus grafted on CTV resistant or tolerant rootstock. In 2010, the CTV eradication program changed to selective removal of only potentially severe strains as defined as those reacting to CTV MCA13 monoclonal antibody. Recently, non-T30 genotypes associated with both mild and severe strains of CTV have been detected in California orchards. To elucidate the basis of recent changes in CTV genetic diversity, more than 300 CTV isolates collected from 1960-2010 across all major citrus-growing regions in California were evaluated. CTV isolates tested were from in planta collections maintained at the University of California Citrus Clonal Protection Program, Riverside, CA and the Central California Tristeza Eradication Agency, Tulare, CA. These CTV strains provide a valuable historical sample of past CTV occurrence. Full-length sequencing of the major coat protein (CP) gene and/or PCR amplification with molecular markers targeting different CTV genome regions showed T30 genotypes were abundant but a few T36-, VT- and B165-like strains were also present at some point in time. Several nonstandard CTV genotypes were also identified. The genetic diversity of CTV strains documented in this study provides a basis for development of CTV management strategies such as cross-protection and provides insight into interactions amongst CTV strains as well as interactions that might occur with the introduction of virulent CTV strains.