Superinfection of Orange Trees Containing Mild Isolates of Citrus Tristeza Virus with Severe Florida Isolates of Citrus Tristeza Virus. C. A. Powell, University of Florida, Institute of Food and Agricultural Sciences, Agricultural Research and Education Center, Fort Pierce 34954. R. R. Pelosi, and M. Cohen. University of Florida, Institute of Food and Agricultural Sciences, Agricultural Research and Education Center, Fort Pierce 34954. Plant Dis. 76:141-144. Accepted for publication 25 July 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0141.

The ability of four mild isolates of citrus tristeza virus (CTV) to suppress the spread of Florida severe isolates of CTV into Valencia sweet orange trees propagated on sour orange rootstock was assessed by symptom development over an 8-yr period. Decline symptoms occurred in some of the trees containing each of the mild isolates, as well as the unprotected (no mild isolate) control trees, within 3 yr after planting. After 5 yr, the percentage of decline in trees infected with the four mild isolates was 28, 22, 27, and 25, respectively, compared with 39% for the unprotected control trees. After 8 yr, the percentage of trees with symptoms (stunting or decline) was 75, 76, 74, and 73, respectively, compared with 86% for the control. Eight years after planting, a monoclonal antibody to CTV (MCA13) reacted with 100, 99, 92, and 19% of the extracts from trees with decline and stunting, stunting, decline, or no symptoms, respectively. A second monoclonal antibody (3DF1) reacted with extracts from all of the trees.