|Yokomi, Raymond - Ray|
Submitted to: Book Chapter
Publication Type: Book / chapter
Publication Acceptance Date: 8/10/2005
Publication Date: 3/1/2010
Citation: Yokomi, R.K., Polek, M., Gumpf, D.J. 2010. TRANSMISSION AND SPREAD OF CITRUS TRISTEZA VIRUS IN CENTRAL CALIFORNIA. In: Karasev, A.V., and M.E. Hilf, editors. Citrus Tristeza Virus Complex and Tristeza Diseases. APS Press, St. Paul, MN. p. 151-165. Interpretive Summary: The transmission and spread of Citrus tristeza virus (CTV) in California are reviewed in the context of current control measures. The main vector of CTV in California is the aphid, Aphis gossypii which occurs as two separate biotypes: the melon aphid; and the cotton aphid. These aphids are host adapted and are genetically distinguishable by Random Amplified Polymorphic DNA (RAPD) patterns by polymerase chain reaction (PCR) and specific primers. Since citrus is grown in four geographically distinct areas in California, important environmental and varietal differences are discussed which impact virus spread, transmissibility and cultivar susceptibility. Differences between A. gossypii and the highly efficient CTV vector, Toxoptera citricida, are discussed. The diverse range found in the aphid transmissibility of local CTV isolates by the cotton aphid are discussed in relation to the disease spread rates and the eradication program for CTV in the San Joaquin Valley. The biocharacterization and genotype of California CTV isolates are also reviewed and updated.
Technical Abstract: The topic of aphid transmission of Citrus tristeza virus (CTV) by Aphis gossypii is reviewed and an update on the genotypes and transmissibility of San Joaquin Valley CTV isolates are provided. This article includes data presented in a symposium on CTV at the annual meeting of the American Phytopathological Society in Anaheim, Calif. in August 2004. CTV incidence continued to spread slowly in a non-exponential fashion even in fields with disease incidence as high as 45% in central California between 1996 and 2004. Using the cotton aphid biotype of Aphis gossypii, most of the local isolates had low vector transmissibility (<1% to 4%) but some isolates with high transmission profiles (32 to 64%) were found. Despite this, in Kern County where CTV eradication continues, CTV incidence remains very low (~0.5%) indicating that CTV suppression is still being achieved. The CTV isolates are not causing economic damage in existing cultivars on tolerant or resistant rootstocks. Nearly all isolates examined had a genotype like the T30 mild isolate from Florida. Some of these isolates induced some stem pitting in Madam Vinous and/or grapefruit in the greenhouse. A few isolates had atypical reaction pattern to the multiple molecular markers used. A CTV isolate called Dekopan was obtained from a local field in which young interplants were topworked with budwood illegally imported from Japan. The Decopan isolate caused severe stem pitting and seedling yellows and contained a mixture of T3 and VT genotypes. All trees infected or propagated by this source have been destroyed.