Molecular cytogenetic evidence for a high level of chromosome pairing among different genomes in Triticum aestivum -: Thinopyrum intermedium hybrids

Intergeneric hybrids (ABDJJ(s)S genomes) were ade between Triticum aestivum cv. Chinse Spring (CS) and Thinopyrum intermedium. Genomic in situ hybridization (GISH) using genomic DNA probes from Pseudoroegneria libanotica (Hackel) D.R. Dewey (genome S, 2n = 14) was used to study chromosome pairing among J, J(s), S and wheat ABD genomes in the hybrids. It was shown that in the hexaploid (ABDJJ(s)S) hybrids, high pairing occurred among wheat chromosomes and among Thinopyrum chromosomes. A closer relationship was observed among the three genomes of Th. intermedium than among the three genomes of T. aestivum. It was further discerned that S genome chromosomes paired with J- and J(s)-genome chromosomes at a high frequency. The frequency of heterologous pairing between S and J or S and J(s) chromosomes was higher than those between J and J(s) chromosomes, indicating that the S-genome was more closely related with these two genomes. Our results provided direct molecular cytogenetic evidence for the hypothesis that S-genome chromosomes are genetically similar to the J-genome chromosomes and, therefore, genetic exchange between these genomes is possible. The discovery of a close relationship among S, J and J(s) genomes provides valuable markers for molecular cytogenetic analyses using S-genomic DNA probes in monitoring the transfer of useful traits from Thinopyrum species into wheat.