Characterization of natural orchardgrass (Dactylis glomerata L.) populations of the Thrace Region of Turkey based on ploidy and DNA polymorphisms

Determining the ploidy and genetic diversity of a germplasm is necessary before initiating breeding or genetic studies. This study was conducted to characterize the ploidy level of 57 natural populations of orchardgrass (Dactylis glomerata L.) collected from the ranges of Thrace region of Turkey and the diversity among populations based on RAPD (Random Amplified Polymorphic DNA) markers. Flow cytometry was used to determine nuclear DNA content (pg 2C^-1 = DNA content of a diploid somatic nucleus) of 6 plants for each population. Nuclear DNA contents were correlated to ploidy level with root tip chromosome counts on selected plants. On the basis of this study, mean nuclear DNA content of orchardgrass was determined as 9.5 pg ± 0.33 (with 95% confidence interval) while all the plants used in chromosome counting were determined to be tetraploid, with 2n = 28 mitotic chromosomes, suggesting that diploid orchardgrass plants are likely very rare or absent in ranges of Thrace region of Turkey. In the RAPD assay, over 40 polymorphic fragments were generated which allowed some populations to be distinguished from the rest by unique markers. A cluster analysis was performed using Nei's (1972) genetic distance index with an unweighted pair group method with arithmetic mean (UPGMA). The cluster analysis indicated that there is a high level of gene flow among natural orchardgrass populations and therefore genes distributed quite homogeneously through out the region. The results of this study can be useful in the development of Dactylis germ plasm collection strategies in Thrace region for breeding purpose.