rDNA chromatin condensation patterns in populations of T. mirus with dominant (C, D, population 2601 plant no. 0-10) and codominant (E, F, population 2602 plant no. 7) phenotypes. T. miscellus (H) was an individual from population 2604 (plant no. 4). Diploid T. dubius, T. porrifolius, and T. pratensis progenitors are in A, B, and G, respectively. rDNA was visualized by FISH to root-tip metaphase (A–C, E, G, H) and interphase (D, F) using FITC-labeled 35S rDNA probe (green fluorescence) and biotin-labeled 5S rDNA detected with avidin-Cy3 (red fluorescence). Nuclei were counterstained with DAPI for DNA (blue fluorescence). Note: in C, the rDNA sites that show some decondensation have large, linked 5S rDNA sites (arrows); in F and D, note the condensed extranucleolar rDNA sites (arrows).