Citrus Tristeza Virus and Its Aphid VectorToxoptera citmicida: Threats to Citrus Production in the Caribbean and Central and North America

Abstract

The CTV-BrCA complex represents a real threat to citrus production in the countries of the Caribbean Basin and Central and North America. The promptness in recognizing the situation by scientists, government officials, and citrus growers of this geographical area will pay dividends by delaying the occurrence of CTV epidemics. Immediate strategies should include preventing any further introduction of any severe CTV isolate into the region, and preventing any further dissemination of the virus via infected budwood. Continued education is essential to make prevention work as well and as long as possible. Eradication and suppression should be considered where the number of infected trees is small and they are restricted to well-defined locations. Largescale suppression should be guided by analysis of cost-benefit ratios and accurate survey information. Long-range movement of plant materials infested with the BrCA should be carefully avoided. Field evaluation of alternate rootstocks is essential in all areas where sour orange is threatened by CTV. Intermediate strategies include deployment of MSCP as other options fail, especially in the context of an integrated pest management scheme (61). Long-range strategies include development of immune scion varieties through genetic engineering and breeding. Several areas that need additional research have been identified by scientists and citrus growers at the various international workshops held in Costa Rica in 1991 and in Venezuela in 1992 (27,29). These areas are summarized as follows: 1) development of rapid methods to differentiate among mild, DI, and SP strains of CTV; 2) development of virus resistance in commercially desirable cultivars by either biotechnology methods, including somatic hybridization, production of transgenic plants, and genetic engineering approaches, or conventional breeding to transfer the CTV immunity present in some citrus relatives into acceptable cultivars; 3) gathering of data on distribution and spread of CTV, as affected by strains of CTV, vector type, and dynamics, hosts, and location effects; 4) developing a better understanding of virus-aphid relationships to determine how CTV is affected by aphid species, virus strain, and hosts; 5) developing biological control methods for the BrCA as part of an integrated pest management system to reduce spread of CTV; and 6) developing improved methods of MSCP