Genomic in situ hybridization (GISH) and Southern hybridization of genome-specific RAPD markers were used to demonstrate that the E genome (including E^e and E^b from Thinopyrum elongatum and Thinopyrum bessarabicum, respectively) and the St genome (from Pseudoroegneria species) were the two basic genomes in Thinopyrum ponticum. GISH also revealed that the centromeric region may be the critical area that discriminates the St genome from the E genome in Th. ponticum. Of the seven partial amphiploids isolated from backcrossed progenies of Triticum aestivum × Thinopyrum ponticum hybrids, two (lines 693 and 7631) have eight pairs of chromosomes from the E^e and (or) E^b genomes. Four partial amphiploids (lines 784, 68, 7430, and 40767-1) have an incomplete St genome, i.e., six pairs of chromosomes of St and one pair of chromosomes from E^e or E^b. In a heptaploid individual of the partial amphiploid 40767-2, there were four pairs of St chromosomes, one pair of St/1B Robertsonian translocation chromosomes, one pair of St/E translocation chromosomes, and one pair of E^e or E^b chromosomes. The isoelectric focusing of Est-5, Est-4, β-Amy-1, α-Amy-1, and α-Amy-2 and the RAPD data generated with 24 decamer primers on five partial amphiploids (lines 784, 693, 7631, 68, and 7430) indicated that lines 693 and 7631 had identical genomes from Th. ponticum. The partial amphiploid 784 probably had a set of chromosomes completely different from those of 693 and 7631. These results indicate that genome recombination usually occurred during the formation of new polyploid lines. Key words : Thinopyrum ponticum, wheat, partial amphiploid, GISH, isozyme, RAPD.

To elucidate the genome constitutions of the tetraploid (2n = 4x = 28) species Elytrigia caespitosa, Lophopyrum nodosum, and Pseudoroegneria geniculata ssp. scythica and the hexaploid (2n = 6x = 42) Thinopyrum intermedium, meiotic pairing was studied in these species as well as 10 hybrids. Karyotype analysis with aceto-orcein stained root-tip cells was performed for the four species and the hybrids of T. bessarabicum with E. caespitosa, P. geniculata ssp. scythica, and T. intermedium. Karyotype analysis by Giemsa C-banding was carried out with the three tetraploid species and the two triploid hybrids involving T. bessarabicum. The species behaved as strict allopolyploids. All hybrids were male sterile with few stainable pollen grains. It is concluded from the results that the three tetraploid species have the genome formula J^eJ^eSS and T. intermedium has the formula J^eJ^eJ^eJ^eSS. The chromosomes of the J^e and S genomes in these species had C-banding patterns differing from each other and from those of the extant diploid species. Based on these findings, the four species investigated should be placed in the same genus or the same section of a genus. However, new combinations are not proposed at this time pending future taxonomic investigation of the genome constitution of Elytrigia repens (L.) Nevski.Key words: genome, hybrid, meiosis, karyotype, chromosome banding, speciation.

To test the presence of a J genome in the type species of Leymus, L. arenarius, its total genomic DNA and that of tetraploids L. mollis, L. salinus ssp. salmonis, L. ambiguus, L. chinensis, L. secalinus, L. alaicus ssp. karataviensis, and L. innovatus were probed with the 277-bp insert of pLeUCD2, which can hybridize with the J, S, and P but not with the N, R, V, Q, I, T, and ABD genomes. The DNA probe hybridized with PalI- or TaqI-digested total DNAs from Thinopyrum elongatum (J^eJ^e diploid) and T. elongatum × Psathyrostachys juncea (J^eN hybrid), but not with those from L. arenarius (NNNNXXXX octoploid) and all tetraploid Leymus species (NNXX). Attempts to cross diploid Thinopyrum and tetraploid Leymus species yielded only one triploid hybrid, T. elongatum × L. salinus ssp. salmonis. Meiotic chromosome associations at metaphase I of pollen mother cells in the triploid hybrid averaged 19.69 univalents, 0.64 bivalents, and 0.01 trivalents per cell. Chromosome pairings in the tetraploid hybrids of L. mollis × L. salinus ssp. salmonis, and the reciprocal cross, indicate that L. mollis and L. salinus ssp. salmonis shae the same genomic constitution. Both the DNA probe and genome analysis results confirm the absence of the J genome in the seven additional Leymus species tested. Meiotic data indicated that tetraploid Leymus species could not have the genome formula N₁N₁N₂N₂; thus their genome formulas should remain as NNXX until the source of X is identified.Key words: genome, Leymus, DNA probe, Southern blot, meiotic pairing, hybrid.