Abstract
Knowledge of ploidy level and genome size in a germplasm collection is critical before studying genetic diversification of different environmental range in grasses and other plants. We assessed the geographic patterns in ploidy level and genome size of 216 individuals of Cynodon dactylon (L.) Pers. (common bermudagrass) by flow cytometry of accessions sampled from 16 geographic sites along a latitudinal gradient from 22°35′ N to 36°18′ N across China. Flow cytometry histograms combined with mitotic chromosome observations results show that tetraploids were the most frequent ploidy level, constituting 44.91% of all individuals. Nuclear DNA contents were 2.384, 2.419, 2.437, 2.873 and 3.288 pg/2C for the diploid, triploid, tetraploid, pentaploid and hexaploid, respectively. Higher proportions of polyploid individuals were observed within populations at the highest and lowest latitudes. In addition, monoploid genome size of C. dactylon progressively increased with increasing ploidy level. Temperature and precipitation had the influence on ploidy level for all the sites. The relationship between ploidy level and geographic distribution for C. dactylon will facilitate the utilization of this species for biological and genetic research.
Highlights
IntroductionOf the 690 C. dactylon germplasm accessions collected across Australia, the most commonly observed ploidy levels were tetraploids (61%) followed by triploids (14%), diploids (11%), pentaploids (0.003%) and hexaploids (0.01%; Jewell et al 2012)
The wind-pollinated Cynodon dactylon (L.) Pers. is widely distributed in temperate and tropical regions of the world and comprises diploid (2n = 2x = 18) and polyploid cytotypes which are used for turfgrass, pasture, forage, soil stabilization, and remediation in arid and semiarid regions (Taliaferro et al 2004)
The numbers of chromosomes observed under the light microscope agree with ploidy levels previously inferred by flow cytometry (Fig. 3)
Summary
Of the 690 C. dactylon germplasm accessions collected across Australia, the most commonly observed ploidy levels were tetraploids (61%) followed by triploids (14%), diploids (11%), pentaploids (0.003%) and hexaploids (0.01%; Jewell et al 2012). These five groups of ploidy levels were found in Turkey among 182 C. dactylon accessions (Gulsen et al 2009). Genome sizes and ploidy levels of warm-season grass species, such as Cynodon spp., Paspalum spp. and Zoysia spp., have been described using flow cytometry (Jarret et al 1995; Johnson et al 1998; Kang et al 2008; Schwartz et al 2010)
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