The karyotype of Elymus mendocinus (Poaceae; Triticeae) from Argentina studied by banding techniques

The karyotype of Elymus mendocinus (2n = 8x = 56) was investigated by Giems a C-banding and N-banding, and AgNO3 staining. The chromosomes were large ( 7-13 mu m). The chromosome complement consisted of 22 metacentric and 6 sub metacentric pairs. Two metacentric and one submetacentric pairs had satelli tes on the short arms. One of the metacentric pairs had large satellites. T he other satellites were small. The number of SAT-chromosomes was verified through AgNO3 staining confirming the presence of up to 6 nucleoli at inter phase. The C-banding pattern comprised small to large C-bands at telomeric positions in all short arms except one and in most of the long arms. A few, mostly small bands were located at distal, intercalary positions. The smal l satellites were entirely heterochromatic. The amount of constitutive hete rochromatin (14%) was among the highest recorded in the Triticeae. Except i n 12 chromosome pairs, incl. the 3 satellited ones, the overall similarity of the C-banding patterns of most chromosomes prevented a safe identificati on of homologues. Additionally, the level of identified banding pattern pol ymorphism was low, but supports an outbreeding nature of the species. N-ban ding produced no bands. A similar distribution of large C-bands and lack of N-banding have previously been observed in Psathyrostachys huashanica. Thi s agrees with the presence of the Ns genome and the absence of the H genome in E. mendocinus (DUBCOVSKY et al. 1997), and suggests the absence of the pivotal St genome of Elymus. However, lacking further evidence we propose t o retain the species in Elymus.