COMPARISON OF THE GIEMSA C-BANDED KARYOTYPES OF THE 3 SUBSPECIES OF PSATHYROSTACHYS-FRAGILIS, SUBSPP, VILLOSUS (2X), SECALIFORMIS (2X, 4X),AND FRAGILIS (2X) (POACEAE), WITH NOTES ON CHROMOSOME-PAIRING

The karyotypes of diploid P. fragilis subsp. villosus (2n = 2x = 14) a nd tetraploid subsp. secaliformis (2n = 4x = 28) were studied by Giems a C- and N-banding, and AgNO3 staining and compared with the karyotype of subsp. fragilis (2x). The complements of subsp. villosus and subsp . fragilis were similar, with 8 metacentric and 6 SAT-chromosomes, one metacentric and two submetacentric pairs, with small to minute, polym orphic, heterochromatic satellites. The complement of subsp. secalifor mis on the whole agreed with a doubling of the complement of diploid P . fragilis, suggesting autopolyploidy. Only the presence of 12 nucleol i in interphases identified 6 SAT-chromosome pairs. In subsp. villosus one or two extra micronucleoli indicated a chromosome pair with very low nucleolus-forming activity, bringing the number of SAT-chromosome pairs to 4. This number may be a characteristic of Psathyrostachys. Be sides very small, inconsistently observed bands, the C-banding pattern consisted of 0-3 small bands per chromosome at intercalary and termin al locations, and at NORs. The level of banding pattern polymorphism w as low, but enough to indicate that the taxa are outbreeders. Similari ties in chromosome morphology and C-banding patterns identified homolo gy of all chromosomes of subsp. villosus, but for 12 pairs only in sub sp. secaliformis. Between plants, reliable identification of homology and homoeology (subsp. secaliformis) was possible only for the SAT-chr omosomes and the shortest metacentrics. Chromocentres were very small and the amount of constitutive heterochromatin was low. N-banding stai ned chromosomes uniformly. The basic karyotypes of the P. fragilis tax a were similar to those of P. juncea, P. lanuginosa, and P. stolonifor mis supporting a close relationship and the presence of a common genom e, N. NORs had different nucleolus-forming activities. Meiotic analysi s demonstrated a high level of bivalent pairing in the three taxa. A c hromosomal rearrangement was suggested in subsp. villosus. The low mul tivalent frequency in subsp. secaliformis indicates the presence of a pairing regulation mechanism. The majority of chiasmata were interstit ial. Pollen grain size discriminated between diploid and tetraploid ta xa. The existence of a diploid cytotype of subsp. secaliformis is supp orted by pollen measurements of herbarium material.