Characterization of genomes and chromosomes in partial amphiploids of the hybrid Triticum aestivum x Thinopyrum ponticum by in situ hybridization, isozyme analysis, and RAPD.

Genomic in situ hybridization (GISH) and Southern hybridization of genome-specific RAPD markers were used to demonstrate that the E genome (including Ee and Eb 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 x Thinopyrum ponticum hybrids, two (lines 693 and 7631) have eight pairs of chromosomes from the Ee and (or) Eb 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 Ee or Eb. 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 Ee or Eb 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.