Evolutionary karyotypic variation in Bromus tomentellus populations

Abstract

Six populations of Bromus tomentellus were selected based on their morphological characteristics to investigate their karyotypes. Preparations were made using fresh grown root tips. Saturated α-bromonaphtaline, glacial acetic acid and ethanol, 1 N HCl and hematoxiline were used for pre-treatment, fixative, hydrolyser and chromosome staining agent, respectively. Karyotypic data were recorded on well-prepared cells at metaphase stage containing a complete set of chromosomes. The studied populations differed in their ploidy levels and karyotypic characteristics. Several statistical parameters were estimated on the data to compare the karyotypes of the populations. UPGMA method of cluster analysis was performed to classify the populations based on their karyotypic characteristics. Finally, Pearson correlation coefficient was estimated for all paired combinations of the karyotypic characteristics to investigate their inter-relationships. The populations possessed 3 ploidy levels (2n=42, 70 and 84). Two populations showed the highest ploidy level so far recorded on Bromus tomentellus (dodecaploid, 2n=84). The size of the chromosomes among the studied populations varied from 3.1 μm to 7μm. The highest and the lowest TF% values were 45.05 and 43.45, respectively. DRL presented different scheme of asymmetry for the populations. On the whole the higher ploidy levels showed lower DRL, or more symmetric karyotypes. The estimated correlation coefficients between the characteristics revealed that DRL is negatively correlated to the ploidy level (r=-0.95). In contrast, TF% is not correlated to any other karyotypic characteristics including ploidy level that imply TF% is more reliable for comparing karyptypic asymmetry of different ploidy levels. © 2006 The Japan Mendel Society.