Identification of a barley chromosomal interchange using N-banding and in situ hybridization techniques

The combination of N-banding and in situ hybridization was used to illustrate the rapid identification of the chromosomes involved in a newly formed chromosomal interchange (reciprocal translocation) in barley. The plant heterozygous for the interchange was derived from the backcross of 'Su Pie', a two-rowed Chinese winter barley cultivar (2n = 2x = 14), with pollen from a triploid interspecific F1 hybrid (2n = 3x = 21) obtained from the cross of 'Su Pie' × tetraploid Hordeum bulbosum accession GBC141 (2n = 4x = 28). Pollen mother cells of the interchanged plant exhibited one quadrivalent and five bivalents in 97.8% of cells. Partial sterility of florets was observed in spikes obtained from self-pollination and the plants morphologically resembled barley. Barley chromosomes were readily identified by N-banding from root-tip cells with one band missing from the short arm of one of the pair of chromosome 4. N-banding of metaphase I of meiosis revealed that chromosomes 1, 2, and 5 were not involved in the interchange. In situ hybridization with a rDNA probe showed that chromosomes 6 and 7 were paired as bivalents. In conclusion, chromosomes 3 and 4 are involved in the interchange with the breakpoint in the short arm of chromosome 4 between the two proximal N-bands. The use of chromosome-specific DNA probes for chromosome identification using in situ hybridization is proposed.Key words: barley, chromosomal interchange, N-banding, in situ hybridization, rDNA.

Cytogenetic relationship within cultivated Brassica analyzed in amphihaploids from the three diploid ancestors

To investigate the factors controlling evolutionary differentiation within the genus Brassica, chromosome pairing in amphihaploids from crosses between the three elementary diploid species B. campestris (AA), B. oleracea (CC), and B. nigra (BB) was analyzed. The amphihaploid AC showed a high amount of pairing, while the two amphihaploids AB and BC, both including the genome of B. nigra, exhibited only low degrees of chromosome association. By the occurrence of tetra- and penta-valents, auto- as well as allo-syndetic pairing was demonstrated to exist in the AC amphihaploid. True homologous pairing between the genomes A and C was deduced from the occurrence of chromosomal interchange configurations. Although the genomes of B. oleracea and B. campestris are evolutionarily distinct, as shown by the different number and structure of their chromosomes, their close relationship is readily evident from the high level of pairing observed in the AC amphihaploids. On the other hand, the much lower pairing within the amphihaploids including the B genome is unexpected in view of the hypothesis of a common ancestor for all three of the cultivated Brassica diploids from an ancestral genome with x = 6 chromosomes. It is discussed whether B. nigra is indeed more distantly related to the two other species or whether this genome carries a suppressor of chromosome pairing.Key words: chromosome pairing, amphihaploids, evolutionary relations.