Expanded Strain‐Specific <scp>RT</scp>‐<scp>PCR</scp> Assay for Differential Detection of Currently Known <i>Citrus Tristeza Virus</i> Strains: a Useful Screening Tool

Abstract

Abstract Genotypic characterization of Citrus tristeza virus ( CTV ) strains has progressed significantly, but their phenotypic expression is poorly established as CTV naturally occurs as mixed‐strain populations. A screening system for the analysis of mixed‐strain populations is required for population studies and the correlation with symptom expression. In this study, a published CTV strain‐specific detection assay was expanded and improved to facilitate detection of currently known CTV strains. Supplementary RT ‐ PCR assays were developed for two variant groups of the RB strain and the HA 16‐5 strain, and assays for the T36 strain and generic CTV detection were improved. The value of the strain‐specific assays was shown by the ability to identify the strain components of two CTV cross‐protecting sources, GFMS 35 and LMS 6, used in the South African budwood certification scheme and to demonstrate the segregation of strains in budwood source trees.