Molecular and Cytological Assessment of Genetic Diversity in Stenotaphrum Germplasm.

St. Augustinegrass (Stenotaphrum secundatum L.) is a low input grass adapted to tropical and subtropical regions of the world, and broadly distributed across the southeastern United States. A better understanding of genetic diversity and ploidy level in Stenotaphrum germplasm could be advantageous to the effective use of this germplasm in St. Augustinegrass breeding programs. The objective of this investigation was to evaluate and compare genetic variation at the molecular and cytological levels in all plant introductions (PIs) and cultivars of St. Augustinegrass. AFLP marker and flow cytometry analyses were performed on 21 cultivars, 25 PIs, and two accessions of S. dimidiatum, a close relative of St. Augustinegrass. AFLP based genetic similarities among genotypes ranged from 0.12 to 0.98 with an average of 0.61. The average genetic similarity for cultivars was higher than that of PIs indicating a higher degree of diversity in the latter group.  AMOVA results indicated that 66 and 75% of the total variation could be explained by differences within ploidy level and germplasm type, respectively. Five ploidy levels were identified by flow cytometry. Nuclear DNA contents were in the ranges 1.12-1.36 for diploids, 1.76-1.81 for triploids, 2.29-2.41 for tetraploids, 3.46 for one hexaploid accession, and 4.40 for one octaploid accession. Inferred ploidy levels were verified by performing mitotic chromosome counts. UPGMA cluster analysis and principal coordinate analysis separated genotypes into distinct groups that were based mostly on ploidy levels. These results represent a step forward in the classification of this important turfgrass species.