Diversity in apomictic populations of Paspalum simplex Morong

Abstract

Paspalum is considered a genetic model for studying the sources of genotypic variability and breeding techniques in apomictic plants. Pas­palum simplex is a warm-season forage grass that well represents the genus since it contains different ploidy levels and apomixis is linked to polyploidy. The objective was to evaluate the diversity present within and among apomictic polyploid populations of P. simplex. Germplasm was collected from 17 sites covering the spe­cies’ region of natural distribution. The diversity present at the molecular level within and among populations was evaluated using ISSR markers. Variability for agronomic traits was also evalu­ated by cultivating all populations into the field. The 17 analyzed populations were all polyploid, including 13 pure tetraploid, and 4 mixed tetra­ploid-hexaploid with predominance of the tetra­ploid cytotype. Most of the diversity was pres­ent among polyploid populations (85% of the total variation), and there was not a correlation between genetic and geographical distances. The within-population diversity was low for most populations with the exception of one of them. Each genotype was restricted to a single loca­tion. Variability for initial growth, spring and fall growth, and the extent of the vegetative phase was observed within and among polyploid popu­lations. The within-population variation for these phenotypic traits was mainly due to the presence of one or a few off-type plants. A highly geno­type-specific colonization of new sites appears to occur in P. simplex, and then apomixis medi­ates the formation of uniform populations.