ARS | Publication request: Molecular diversity of Citrus tristeza virus strains collected over the past 50 years and maintained in planta collections in California

Submitted to: International Citrus Congress Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: November 16, 2012
Publication Date: N/A

Technical Abstract: Citrus tristeza virus (CTV), is a serious citrus pathogen. Because severe CTV strains can reduce fruit production and quality, CTV is a regulated pathogen in California. All citrus budwood sources in California citrus nurseries are maintained free of CTV and infected field trees have been removed in quarantine zones. Until recently, the rouging program and low rate of natural spread has limited CTV genetic diversity in California. Most CTV stains have T30-like genotypes which, under California conditions, causes no significant damage of commercial varieties grafted on CTV resistant or tolerant rootstocks. Recently, severe non-T30 strains of CTV have been detected and citrus tristeza has become a re-emerging disease. To elucidate the origin of recent CTV strains, genetic diversity of more than 300 CTV isolates collected from 1960-2008 across all major citrus-growing regions in California were evaluated. These isolates provided a valuable sample of past CTV strains in California. The collections were maintained in planta at the UC Riverside’s Citrus Clonal Protection Program (CCPP) and the Citrus Pest Detection Agency (CPDA), Tulare. Full-length sequencing of the major coat protein gene and/or PCR amplification with multiple molecular markers targeting different CTV genome regions showed T30 genotypes were abundant in California but a few T36-, VT-, T3- and B165-like genotypes were present at some point in time. Several nonstandard CTV genotypes were also identified. The genetic diversity detected provides a basis for development of CTV management strategies such as cross-protection. Moreover, it provides insight into interactions amongst CTV strains as well as that which might occur with the introduction of virulent CTV strains.