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 hybridi zation (GISH) using genomic DNA probes from Pseudoroegneria libanotica (Hac kel) D.R. Dewey (genome S, 2n = 14) was used to study chromosome pairing am ong J, J(s), S and wheat ABD genomes in the hybrids. It was shown that in t he hexaploid (ABDJJ(s)S) hybrids, high pairing occurred among wheat chromos omes and among Thinopyrum chromosomes. A closer relationship was observed a mong 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 hetero logous pairing between S and J or S and J(s) chromosomes was higher than th ose between J and J(s) chromosomes, indicating that the S-genome was more c losely related with these two genomes. Our results provided direct molecula r cytogenetic evidence for the hypothesis that S-genome chromosomes are gen etically similar to the J-genome chromosomes and, therefore, genetic exchan ge between these genomes is possible. The discovery of a close relationship among S, J and J(s) genomes provides valuable markers for molecular cytoge netic analyses using S-genomic DNA probes in monitoring the transfer of use ful traits from Thinopyrum species into wheat.