CTV Vectors and Interactions with the Virus and Host Plants

Abstract

Citrus is a graft-propagated perennial crop, and Citrus tristeza virus (CTV) is readily graft-transmissible. CTV is comprised of a complex of strains and isolates and, in nature, is spread semi-persistently by aphid vectors. Therefore, citrus trees become infected with multiple CTV strains over time. An important step in characterizing a CTV field isolate is to use aphid vectors to “clean” up the CTV population of a source tree to separate strains and eliminate other graft-transmissible agents. Use of Toxoptera citricida or Aphis gossypii will expedite efficient CTV transmission. CTV vector studies require critical coordination of abundant robust and virus-free vector-competent aphid colonies and an insect-proof, climate-controlled greenhouse or growth chamber. CTV donor and healthy receptor plants with young flush growth must be available for virus acquisition and inoculation. Vector optimums for virus acquisition and inoculation are 24 h for each. CTV infection is readily determined by serology using a polyclonal antiserum or a monoclonal antiserum cocktail; whereas, molecular genotyping is conducted with reverse transcription polymerase chain (RT-PCR) or real time quantitavtive RT-PCR (RT-qPCR) with strain-specific primers and probes. However, the phenotype of the aphid-transmitted isolate still requires virus indexing by graft inoculation to a citrus host range and evaluating symptoms such as stem pitting, vein clearing, stunting, and chlorosis.