Habitat fragmentation is one of serious threats to biodiversity of nature in today's world. The present study of a typical steppe species Iris pumila L. (Iridaceae) has analyzed the impacts of geographical isolation and population size on genetic diversity and population structure in conditions of habitat fragmentation. The key indices of population genetic variability calculated from the ISSR markers data were on average as follows: Shannon diversity index (S) – 0.188; unbiased Nei’s gene diversity (He) – 0.123; and the average measure of Jaccard’s genetic distances between individuals within populations – 58.4%. Although the largest population had significantly higher values of S and He, the small and marginal populations also showed a comparable level of variation. Most of the genetic variation of I. pumila was distributed within the populations. A strong correlation was found between Nei’s genetic distances and geographic distances between the populations. According to the Bayesian analysis, genetic structure of the populations was highly homogeneous; however, the presence of admixed genotypes indicated the possibility of gene flow between the populations at present.
Different chromosomal forms of Deschampsia antarctica Desv. (Poaceae), including diploids (2n=26), hypotriploid (2n=36–38) and a genotype with an occasional occurrence of B chromosome (2n=26+0-1B) that originated from southern marginal populations (Argentine Islands region, maritime Antarctic) were studied using molecular cytogenetic, morphometric and biochemical methods. FISH analysis revealed variations in the number of rDNA sites between the diploid and hypotriploid plants. The genome size varied among plants with a different chromosome number and was on average 10.88 pg/2C for diploids and 16.46 pg/2C for hypotriploid. The mean values of leaf length of plants grown in vitro varied within a range of 5.23–9.56 cm. The total phenolic content ranged from 51.10 to 105.40 mg/g, and the total flavonoid content ranged from 1.22 to 4.67 mg/g. The amount of phenolic compounds did not differ significantly between the genotypes, while a variation in the flavonoid content was observed for L59 and DAR12. The diploids did not differ significantly among each other in terms of the number of rDNA loci, but differed slightly in their genome size. The individuals of DAR12 carrying B chromosome were similar to other diploids in terms of their genome size, but statistically differed in leaf length. The hypotriploid had both a greater number of rDNA sites and a larger genome size. No statistical correlations were observed between the genome size and leaf length or genome size and accumulation of phenolic and flavonoid compounds. The results of this study suggest that D. antarctica plants from the southern edge of the range are characterised by the heterogeneity of the studied parameters.