Submitted to: Conference of International Organization of Citrus Virologists
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/20/2004
Publication Date: 6/10/2007
Citation: Garnsey, S.M., Civerolo, E.L., Gumpf, D.J., Paul, C., Hilf, M.E., Lee, R.F., Brlansky, R.H., Yokomi, R.K., Hartung, J.S. 2007. Biological characterization of an international collection of citrus tristeza virus (ctv)isolates. In: Proceedings of Conference of International Organization of Citrus Virologists. p. 75-93. Interpretive Summary: Two hundred sixty six isolates of Citrus tristeza virus (CTV) from 30 countries were evaluated for symptom expressions in a citrus host range in a USDA-ARS quarantine facility in Beltsville, MD. The purpose was to compare virulence of these isolates under uniform conditions so results would be accurate for comparison with other CTV isolates collected from anywhere in the world. CTV isolates varied markedly in ability to induce symptoms and severity which were generally consistent with field observations of these isolates. Different symptom patterns among the five indicators suggested that seedling yellows, decline in sweet orange grafted on sour orange, stem pitting in sweet orange, and stem pitting in grapefruit are independent expressions of CTV pathogenicity and can occur in various combinations. Some general associations between symptoms of some isolates and CTV genotypes and selective reaction to monoclonal antibody MCA13 were observed, however, absolute correlations were not established. These biological characterizations and maintenance of these isolates along with the rest of the CTV collection in Beltsville are a critical resource in research being conducted to gain a better understanding of the genetic determinants of CTV symptomology and for the development of strain specific markers to rapidly identify potentially severe vs. mild isolates of CTV.
Technical Abstract: TECHNICAL ABSTRACT: Symptom expression of 267 different isolates of CTV originating from 30 countries was determined by graft-inoculation of Mexican lime, sour orange, Madam vinous sweet orange and Duncan grapefruit seedlings, and a grafted combination of sweet orange on sour orange rootstock. Testing was conducted over 16 yrs in a USDA quarantine facility at Beltsville, MD. Readings for foliar symptoms and stem pitting in each test were made for 12 months and compared to standard isolates. Plants which remained symptomless were tested by ELISA to verify infection. These standardized tests in a single facility confirmed that the wide range of symptom severity observed can be directly attributed to differences among CTV isolates. The patterns of symptom expression observed in the five indicators indicated that seedling yellows, the decline syndrome in sweet orange grafted on sour orange, stem pitting in sweet orange, and stem pitting in grapefruit are independent expressions of CTV pathogenicity and may occur in various combinations. Associations between symptom expression and reactions to selective serological or molecular markers are also reported.