摘要：

Genetic linkage maps of bermudagrass (Cynodon spp.) species using 118 triploid individuals derived from a cross of T89 [C. dactylon (2n = 4x = 36)] and T574 [C. transvaalensis (2n = 2x = 18)] were enriched with expressed sequence tags-derived simple sequence repeat (EST-SSR) markers. Primers were developed from 53 ESTs containing SSRs producing 75 segregating markers from which 28 could be mapped to the T89 and T574 genetic maps. With the addition of previously generated marker data, 26 T89 linkage groups and eight T574 linkage groups were formed using a log-of-odds (LOD) value of 4.0. The T89 and T574 linkage maps spanned 1055 cM and 311.1 cM and include 125 and 36 single-dose amplified fragments (SDAFs), respectively. Many of the SDAFs displayed disomic segregation and thus T89 may be a segmental allotetraploid or an allotetraploid. The additional EST-SSR markers add value to the maps by increasing marker density and provide markers that can be easily transferred to other bermudagrass populations. Furthermore, EST-SSRs can be immediately used to assess genetic diversity, identify non-mutated cultivars of bermudagrass, confirm pedigrees, and differentiate contaminants from cultivars derived from 'Tifgreen'. Bermudagrass is a warm-season grass used as turf for home lawns, public parks, golf courses, sports fields, and for forage and soil conservation (Zhang et al., 1999). Common bermudagrass [Cynodon dactylon (2n = 4x = 36)] was first introduced into the United States during the colonial period (Kim et al., 2008) and has spread throughout the southern United States. Cultivar releases from Tifton, GA, are predominantly generated by crossing african bermudagrass [Cynodon transvaalensis (2n = 2x = 18)] with common types to produce sterile triploid hybrids with improved turf qualities, although other turfgrass breeding programs have recently developed improved vegetatively or seed-propagated tetraploid cultivars (Riley, 2000; Taliaferro et al., 2003). Bermudagrass has many advantageous traits promoting its pervasive use. Bermudagrass is salt-tolerant (Kim et al., 2008), heat-and drought-tolerant (Utrillas and Alegre, 1997; Walker et al., 2006), and has the ability to spread by stolons, rhizomes, and seeds (Webster et al., 2004). Despite these many qualities, the genes controlling these traits have not been identified and few molecular tools have been developed. Although bermudagrass species are often polyploid, a framework genetic linkage map has been constructed based on single-dose restriction fragments (SDRFs) (Bethel et al., 2006). SDRFs or alternatively single-dose amplification fragments markers (Stein et al., 2007) are present as a single copy on a single chromosome from only one of the parents in the cross. Because SDAFs are present in a 1:1 ratio in the gametes, they can be used for mapping in polyploids regardless of ploidy level or chromo-somal pairing (auto versus allo) (Wu et al., 1992). With SDAF mapping, a linkage map is generated for each parent separately (Fregene et al., 1997). Four homologous sets were formed for the T89 (tetraploid) parental map using 155 SDRFs (Bethel et al., 2006). For the T574 (diploid) parental map, 77 SDRFs formed seven homologous sets (Bethel et al., 2006). With the T89 and T574 maps having 61% and 62% marker coverage of their genomes (Bethel et al., 2006), respectively, additional markers are needed to fill in gaps as well as to link homologous linkage groups. Recently, bermudagrass resistance gene analogs were identified and added to the map (Harris et al., 2010). Increased marker density is needed to map traits of interest such as nematode tolerance, root length, and turf quality that may be different between the two parents. Thus, the objective of this research was to develop EST-SSR markers that can be used to identify homologous linkage groups and enrich the bermuda-grass genetic map. Furthermore, these SSR markers were evaluated to determine if differences can be generated between a set of very closely related genotypes and for the identification of contaminants among monocul

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