Genetic and Reproductive State Assessment of Ulmus pumila and U. suberosa Invasive Populations in the Dnieper Steppe under Climate Change

The degree of intraspecific genetic polymorphism and heterozygosity, the germinal death, viability of seeds, and the cytogenetic state of vegetative Ulmus pumila and U. suberosa meristems were analyzed for determining the mechanisms of plant population invasiveness in the steppe Dnieper region under climate changes. The studied U. pumila population were different in terms of germinal (embryonic) death, seed viability and seed productivity. Populations grown under more favorable environmental conditions had the best reproductive, physiological and genetic conditions. For the majority of used microsatellite loci, population studies were characterized by a relatively low level of genetic variability, an excess of homozygous genotypes and a deficiency of heterozygotes, which indicated a certain level of inbreeding of the analyzed plants. The highest deficiency of heterozygotes was found in U. pumila populations with high stand density and significant indices of germinal seed loss; smaller deficits were in populations with a larger area and low stand density and, accordingly, low rates of germinal death. The low index of chromosomal rearrangements in the vegetative meristems also confirmed an insignificant level of genetic variability and the probable absence of hybridization and genetic homeostasis in U. pumila . The U. suberosa population was characterized by increased indices of germinal death, seed damage and low seed productivity, which correlated with an excess of homozygous genotypes. All U. suberosa specimens were monomorphic by the microsatellite loci. In general, by genetic and reproductive indices, seed reproduction and distribution of U. pumila in the steppe Dnieper region is not significantly limited under climate change. At the same time, seed reproduction of U. suberosa may be limited.