Ploidy Level and DNA Content Determination of Perennial Ryegrass Germplasm by Using Flow Cytometry.

Perennial ryegrass (Lolium perenne L.) is a commonly used cool-season turfgrass species. Both diploid (2n=14) and tetraploid (2n= 28) perennial ryegrass materials exist in the germplasm collection. The objective of this study was to determine the ploidy level and DNA content of perennial ryegrass germplasm to establish a diploid natural mapping population for marker-trait association analysis. A total of 200 accessions of perennial ryegrass were obtained from the USDA National Plant Germplasm System (NPGS). Three independent samplings of young leaf tissues were conducted, and the DNA content was analyzed using the flow cytometry technique. Among the 200 accessions, 194 diploid and 6 tetraploid were identified. The average DNA content was 5.60 ± 0.21 pg/2C for the diploid and 11.45 ± 0.38 pg/2C for the tetraploid, respectively. DNA content in both the diploid and the tetraploid was correlated with chromosome numbers in the root tips counted under a microscope. The results provide important information for genetic research and cultivar improvement of perennial ryegrass.