Karyological differentiation among bread wheat cultivars (Triticum aestivum L.) with distinct breeding statuses and growth habits

The assessment of intraspecific variability of wheat has been relevant for years. Although most modern wheat cultivars are considered to be pure lines, the heterogeneity of varietal populations is one of the mechanisms for maintaining population homeostasis. It is possible that the high evolutionary stability of constitutive heterochromatin and its stable distribution within chromosomes will allow us to use karyological analysis not only for studying the genesis and taxonomy of Triticum L., but also for studying the intraspecific diversity of wheat. In this regard, a classification of 87 Russian cultivars of common wheat differing in breeding status (landraces and modern cultivars) and growth habit (spring and winter) was carried out using two alternative approaches for assessing karyograms. The first approach uses the qualitative assessment of karyograms based on the distribution of C-bands on chromosomes. We also proposed that quantification of karyograms based on the size of C-bands would make the classification of cultivars more adequate. The variability, informative value and resolution of diagnostic features, trends in grouping cultivars, and their associations with the breeding status and growth habit were studied. A high potential of karyotyping with C-banding in discriminating modern cultivars by growth habit, as well as in separating winter cultivars from landraces has been revealed. In terms of the tested karyological features, the homogeneity of modern cultivars was higher than that of local cultivars, and the homogeneity of winter wheat was higher than that of spring wheat. The obtained classification reflects the preservation of high similarity in the karyograms of modern spring cultivars and landraces, as well as the low distinguishability between the karyograms of landraces differing in growth habit. A comparative analysis of the classifications of 20 cultivars using C-banding and SNP genotyping (3,126 polymorphic markers) suggests that studying the karyotypic variability allows us to infer a more accurate differentiation of wheat varietal populations based on the breeding status than using SNP markers that detect genetic variability, especially when the number of diagnostic features is limited.