Publication Date

8-1-2001

Degree Program

Department of Agriculture

Degree Type

Master of Science

Abstract

Isolates of Citrus Tristeza Virus (CTV) in Belize may be causing inverse stem pitting, stunting, and slow decline on sweet and sour orange rootstock combination on field trees. One isolate on Cleopatra mandarin rootstock expressed no field symptoms but may be a possible source of a detrimental isolate to more susceptible citrus rootstock combinations. Field plants and field source inoculated indicator plants were used in this study. The first objective was to determine whether field trees of sweet Valencia orange trees that expressed symptoms of CTV would test positive to a polyclonal (mild and severe symptoms) and a monoclonal (severe decline) antibody. Of the 81 trees tested, 56% tested positive to a polyclonal antibody G-604. None of the trees tested positive to the monoclonal antibody MCA-13. The second objective was to determine the biological and serological reactivity on host indicator plants of some of the most symptomatic trees having highest optical density value readings from the ELISA test. Mexican lime showed mild to moderate vein clearing on three of the isolates tested, while sweet orange showed mild to moderate translucent veins on two of the isolates tested. Four isolates from the indicator host plants tested positive to polyclonal antibody G-604 but none tested positive to MCA-13. The third objective was to determine if there were any differences among the nucleotide sequences of three CTV isolates. The CTV coat protein gene (CPG) of isolates which reacted to a polyclonal antibody G-604 but not to monoclonal antibody (MCA-13) was selectively amplified by polymerase chain reaction from infected tissue extracts and sequenced using negative sense CN 407 primer. All three isolates revealed between ninety-eight and ninety percent significant identities to known CTV isolates previously characterized from citrus growing regions around the world.

Disciplines

Agriculture | Agronomy and Crop Sciences