|Yokomi, Raymond - Ray|
Submitted to: Conference of International Organization of Citrus Virologists
Publication Type: Abstract Only
Publication Acceptance Date: 10/22/2010
Publication Date: 11/7/2010
Citation: Yokomi, R.K., Saponari, M., Metheney, P., Vidalakis, G. 2010. Genetic differentiation and biology of Citrus tristeza virus populations spreading in eradicative and non-eradicative areas of California [abstract]. Conference of International Organization of Citrus Virologists. 31:s27. Interpretive Summary:
Technical Abstract: Previous studies showed Citrus tristeza virus (CTV) isolates collected from the 1970’s in California were closely related to the mild T30 isolate; only a few severe strains such as SY568 (Riverside) and Dekopon (Orange Cove) were found and subsequently eradicated. CTV is now spreading rapidly in some areas of the San Joaquin Valley and, in 2009, management has changed from eradication to selective removal of potentially severe CTV strains. This was based on an assessment of CTV strains from over 1500 trees from groves in Tulare, Kern, Ventura, Riverside and San Diego Co. Isolates were tested for reaction against MCA13, strain-specific markers in conventional and quantitative RT-PCR tests, SSCP and sequencing of the coat protein gene. A genetically diverse set of isolates were then indexed in the greenhouse. CTV isolates from eradication districts nearly always contained a T30 genotype and were mild or induced no symptoms on sweet orange, Duncan grapefruit (DGF), sour orange (SO) or Eureka lemon (EL). Isolates from non-eradication districts were mostly T30 strains, however, single or mixed infections with a non-standard (NS) and/or a T3-like strain were found. Coat protein sequences from NS strains clustered in the same main clade as T36 and were named T36NS. These strains reacted with MCA13 and were mild on Mexican lime, symptomless in other citrus indicators and were poorly transmissible (< 1%) by aphid vectors. T3-like strains in single or mixed infections with T30 induced strong seedling yellows in SO, DGF, and EL. Thus, California CTV strains tested fell into two biological classes: mild with a T30 and/or T36NS genotype; and severe SY strain with a T3 genotype. These data support validation of genotype-specific probes used in field surveys to differentiate economically important CTV strains for selective removal.