Diversidade genética, contagem cromossômica, medidas estomáticas e grãos de pólen de Paspalum rawitscheri (Parodi) Chase ex G.H. Rua & Valls (Poaceae)

Abstract

Studies on the characterization, conservation and evaluation of extinction risks in plant species are increasingly necessary for the protection of biodiversity in Brazil. The grass Paspalum rawitscheri (Parodi) Chase ex G.H. Rua & Valls, which occurs in southern Brazil, is threatened with extinction. In this sense, the objective of this work was to provide subsidies for the genetic and cytogenetic characterization of Paspalum rawitscheri (Poaceae), in order to search conservation and management strategies. Samples were collected for analysis of genetic diversity: Santa Maria (24 individuals), São Martinho da Serra (36 individuals), Campestre da Serra (46 individuals) and Vacaria (9 individuals), as well as testimonial material for deposition in the herbarium SMDB. Genetic diversity analysis was performed by comparing ISSR patterns among individuals from different populations, which were visualized on 1.5% agarose gel. For chromosome counting and evaluation of the level of ploidy, young inflorescences of Santa Maria population were used to make the slides. For the analysis of the viability and measurement of the pollen, inflorescences of the populations of Santa Maria and Campestre da Serra were used for the preparation of the slides, being evaluated only two individuals per population. The fresh leaves of two individuals per population, Santa Maria, São Martinho da Serra and Campestre da Serra, were used for the analysis of the stomatal measurements, this evaluation was done through the epidermal impression method of the adaxial leaf face. Statistical analysis of the molecular markers was performed with the Structure and GenAlEx softwares. The comparison of the pollen viability, stomatal measurements and pollen grains of the different individuals was done using the Tukey test at a 5% probability of error. The analyzed populations presented widely varied polymorphism rates between the populations (between 29,26 to 67,48%), low genetic diversity (h= 0,130 to 0,217) and low population structure. The Bayesian analysis determined that the individuals are inserted in four clusters, with admixture in the clusters. The stomatal and pollen grains of the populations showed a significant difference, mainly in relation to the height (equatorial diameter), where variation occurred among all the analyzed populations. For the pollen viability the Alexander reactive dye showed a significant difference between the populations of Santa Maria and Campestre da Serra. The population of Santa Maria presented as diploid, 2n = 20 chromosomes, being the only population that could be made the chromosome count. It is concluded that the populations of P. rawitscheri present low population structure, with low genetic diversity and reduced pollen viability for a population. These data may imply a continuous population reduction for the species. With the most pronounced difference between stomata and pollen grains between Santa Maria and Campestre da Serra, there may be a difference in ploidy between these populations, with polyploid individuals in the P. rawitscheri species.