Distribution of rDNA probes and different tandem repeats on metaphase chromosomes of perennial grass species: Th. bessarabicum W6 10232 (a–c) and PI 531711 (d), Th. intermedium (e, f); and Th. ponticum (g, h). Probe combination in a, e, g pTa71, red + pTa794, green b, h pSc119.2, green + pAs1, red c pSc119.2, green + pTa-535, red d pSc119.2, green + pAesp_SAT86, red f pAs1, red. The letters from A to K designate pairs of homologous chromosomes identified in Th. intermedium (e) or Th. ponticum (g) mitotic cells based on characteristic patterns of 5S and/or 45S rDNA probes. Yellow arrows (b–d) show position of secondary constrictions on Th. bessarabicum chromosomes. 5S rDNA sites on Th. intermedium (e) or Th. ponticum (g) chromosomes are indicated with small arrows. White arrows (h) show homologous Th. ponticum chromosomes with contrasting pSc119.2 patterns. Scale bar: 10 µm.