CHARACTERIZATION OF GENOMES AND CHROMOSOMES IN PARTIAL AMPHIPLOIDS OFTHE HYBRID TRITICUM-AESTIVUM X THINOPYRUM-PONTICUM BY IN-SITU HYBRIDIZATION, ISOZYME ANALYSIS, AND RAPD

Genomic in situ hybridization (GISH) and Southern hybridization of gen ome-specific RAPD markers were used to demonstrate that the E genome ( including E(e) and E(b) from Thinopyrum elongatum and Thinopyrum bessa rabicum, respectively) and the St genome (from Pseudoroegneria species ) were the two basic genomes in Thinopyrum ponticum. GISH also reveale d that the centromeric region may be the critical area that discrimina tes the St genome from the E genome in Th. ponticum. Of the seven part ial amphiploids isolated from backcrossed progenies of Triticum aestiv um x 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 chromosom es from E(e) or E(b) In a heptaploid individual of the partial amphipl oid 40767-2, there were four pairs of St chromosomes, one pair of St/1 B Robertsonian translocation chromosomes, one pair of St/E translocati on chromosomes, and one pair of E(e) or E(b) chromosomes. The isoelect ric focusing of Est-5, Est-4, beta-Amy-1, alpha-Amy-1, and alpha-Amy-2 and the RAPD data generated with 24 decamer primers on five partial a mphiploids (lines 784, 693, 7631, 68, and 7430) indicated that lines 6 93 and 7631 had identical genomes from Th. ponticum. The partial amphi ploid 784 probably had a set of chromosomes completely different from those of 693 and 7631. These results indicate that genome recombinatio n usually occurred during the formation of new polyploid lines.