Submitted to: Conference of International Organization of Citrus Virologists
Publication Type: Proceedings
Publication Acceptance Date: May 22, 1997
Publication Date: N/A
Interpretive Summary: The brown citrus aphid (BCA) is a highly efficient vector of citrus tristeza virus. Severe losses due to tristeza-induced decline and stem pitting have been experienced in several countries following introduction of the BCA, and severe isolates of tristeza became more prevalent. The recent establishment of BCA in Florida has prompted renewed concern about future effects of tristeza on U.S. citrus production. Through cooperative efforts with scientists in the Dominican Republic, useful data has been collected on the movement of tristeza virus there, following introduction of the BCA. The tristeza virus spread rapidly in the Dominican Republic in sweet orange, but much more slowly in grapefruit. The tristeza isolate being spread so far in commercial plantings in the Dominican Republic is mild, and it has caused little economic impact so far. Spread of more severe isolates is anticipated in the Dominican Republic; however, current information indicates that while the BCA is an effective agent for moving existing isolates, it does not change their severity. The future impact of tristeza in areas of the U.S. that become infested by the BCA will depend on the severity of endemic isolates of tristeza and those isolates which are subsequently introduced from other countries. Exclusion of exotic isolates and careful control of tristeza infection in propagating sources are important control strategies.
Technical Abstract: Rapid increase in the incidence of citrus tristeza virus (CTV) infection occurred in three 20 X 20 tree test plots established in large commercial 4- to 6-year-old sweet orange plantings in the Dominican Republic. In each location, some trees infected with mild isolates had apparently been established via propagation of infected budwood. Samples were from all trees at ca. six-month intervals between September 1992 and May 1995, and these were tested for CTV by DAS-I ELISA. A mixture of two broad-spectrum monoclonal antibodies (MABs) was used for general detection of CTV infection, and the selective MAB, MCA13, was used to detect decline and stem pitting isolates. Initially, CTV incidence in the plots was 1%, 8%, and 50%, respectively. Within 32 months, the CTV incidence had risen to 93%, 48%, and 93%. In a similar plot of Marsh grapefruit on Swingle citrumelo, infection incidence increased from 0% to only 2% during the same period. None of the 1,420 CTV-infected trees found tested positively with MCA13, and no decline was observed. At this time, rapid spread of mild isolates has not affected citrus production; however, spread of severe isolates into commercial plantings remains a future threat.