Biological Characterization of an International Collection of Citrus tristeza virus (CTV) Isolates

Abstract

Symptoms induced by 266 isolates of Citrus tristeza virus (CTV) obtained from 30 countries were evaluated in graft-inoculated Mexican lime, sour orange, Madam vinous sweet orange and Duncan grapefruit seedlings, and sweet orange plants budded on sour orange root-stock. Sequential tests were conducted for 16 yr in a USDA-ARS quarantine facility at Beltsville, MD using consistent protocols. Two standard isolates were included in each test for reference. The isolates tested varied markedly in their ability to induce symptoms in specific indicators as well as in the severity of symptoms. The different patterns of symptoms observed in the five indicators suggested 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. Although some general associations between some symptoms and CTV genotypes and reaction to the selective monoclonal antibody MCA13 were observed, absolute correlations were not established.