Diversity in Diploid, Tetraploid, and Mixed Diploid-Tetraploid Populations of Paspalum simplex

The tetraploid cytotype of Paspalum simplex Morong has a wide geographical distribution and reproduces by apomixis while the diploid grows in a restricted area in northern Argentina and behaves as cross-pollinated. The objective was to evaluate the genetic diversity among and within natural diploid and tetraploid populations of P. simplex growing in sympatry and allopatry by studying the phenotypic variability and DNA polymorphisms. Twenty-three phenotypic traits and 10 inter-simple sequence repeat (ISSR) molecular markers were used for evaluating the variability present in six populations of P. simplex. Two populations were diploid and four were tetraploid. One of the tetraploid populations was sympatric to a diploid population while the rest of the populations were allopatric. A rich diversity was observed for specific traits, especially for seasonal biomass yield, presence of a terminal raceme in the inflorescence, and leaf pubescence. The 2x and 4x populations growing in proximity were closely related. Diversity was higher within diploid populations when compared with the evaluated tetraploid populations. Among the tetraploid populations, the one sympatric with a diploid population exhibited the greatest diversity. Gene flow occurs between 2x sexual and 4x apomictic populations of P. simplex. Diploid populations seem to be the main source of the diversity observed among tetraploid populations.