ABSTRACT. Prevalence of citrus tristeza virus (CTV) isolates causing severe stem pitting symptoms with a high diverse genetic composition represents a threat for citrus crops in Uruguay. This work aimed to characterize viral components of CTV populations segregated by single aphid (Toxoptera citricida) transmission (SAT). Thirty-nine SAT-derived sub-isolates were obtained from six CTV field isolates. Only eight were MCA13 non-reactive, and six of them, together with other three MCA13 reactive sub-isolates, were considered mild by the intensity of their reaction in ?Mexican? lime, ?Madam Vinous? sweet orange, ?Duncan? grapefruit and sour orange indicator plants. Fourteen sub-isolates, including two MCA13 non-reactive, were considered moderate, and the remaining sub-isolates were all MCA13 reactive and with severe reactions in the indicator plants. Sequence comparisons of the p20, p23 and p25 genes showed a high inter (among all isolates and their derived sub-isolates)- and intra (among each isolate and its derived sub-isolates)-specific evolutionary diversity, with the presence of the CTV strains VT, T3, RB, and NC in mixtures of their complex populations. Together, our data revealed the heterogeneity of the Uruguayan CTV populations in these CTV field isolates. The results provide additional biological and molecular information on the complex CTV populations in Uruguay and must be considered for improving the CTV management program. © Sociedade Brasileira de Fitopatologia 2019