Linear differentiation of cereal chromosomes : I. Common wheat and its supposed ancestors.

Using the Giemsa technique of differential staining (the BSG test), we have studies the karyotypes and constructed the idiograms of T. aestivum L. var. 'Diamant' and 'Chinese Spring', T. Monococcum L. v. 'hornemannii' ssp. roles occidentali georgicum Dek., Aegilops squarrosa L. v. 'Meeyeri', T. aestivum. The karyotypes of 'Chinese Spring' and 'Diamant' differ drastically both in total structural heterochromatin content and its localization on the nine morphologically homeologous chromosomes. The rest of the twelve pairs of chromosomes showed no morphological similarity. This indicates considerable differences in the phylogeny of the varieties, and also an absence of unique karyotype in T. aestivum.Three chromosomes of Ae. Squarrosa are similar to those of 'Chinese Spring', yet, on the whole, the chromosomal structural specificity of the diploids studied is so high that we fail to understand the nature of the homology between common wheat and its supposed diploid ancestors.The role of introgression in the evolution of the genomes of Triticum and Aegilops, and also the meaning of the conjugation and BSG tests in resolving the phylogeny, is discussed.