|Polek,, Marylou - CDFA, CCTEA, TULARE, CA|
|Saponari,, Maria - INST. DE VIRO VEG, BARI|
Submitted to: American Phytopathological Society Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: April 10, 2008
Publication Date: July 26, 2008
Citation: Yokomi, R.K., Polek,, M., Saponari,, M. 2008. Genetic diversity of Citrus tristeza virus isolates spreading in Central California. American Phytopathological Society Abstracts. 98:S178. Technical Abstract: A rapid increase in the number of trees infected with Citrus tristeza virus (CTV) was observed in several locations in Tulare, County, CA during 2007. Since trees had been tested annually, these infections represent new infections. Leaf and bark tissue were sampled from infected trees and used for molecular and serological characterizations. Real-time RT-PCR using a generic CTV TaqMan probe detected all isolates. No reactions were obtained when using a CTV-stem pitting TaqMan probe but several samples reacted to a specific TaqMan probe developed for California MCA13 positive isolates which do not induce decline. All isolates had a T30 genotype and SSCP analysis of the CP region showed most isolates had a profile identical to the mild P81 isolate. However, three different SSCP patterns were also observed. Sequencing analysis of the CP gene revealed the presence of at least two different isolates along with the common P81-like isolate. Pairwise alignments from these isolates shared only 91.5% and 90.7% nucleotide identity with mild isolates and supports the notion that they are genetically distinct isolates. Phylogenetic relationships indicated that one isolate was closely related to but distinct from the Florida T36 strain (94% nucleotide identity); whereas the other isolate was in a separate clade along with a grapefruit stem-pitting isolate from Argentina (C269-6) and an aphid-transmitted sub-isolate (P108-35) of the Dekopon isolate, a virulent CTV strain intercepted in central California. Host range biocharacterization of these isolates are ongoing. The rapid increase of infected trees appears to be fairly widespread in some citrus production areas of the Central Valley even in areas that consistently remove CTV-infected trees. We continue to monitor the spread and diversity of these CTV isolates in an effort to explain this trend.