Carpetgrass [Axonopus compressus (Sw.) Beauv.] is a perennial warm-season turfgrass with many excellent characteristics, such as easy establishment and low management. Because of these traits, carpetgrass is often used to conserve soils and highway slopes and is planted as turf in common areas, sports fields, and shady areas in south China and around the world (Xi et al., 2004a). All individuals of carpetgrass are polyploid, with chromosome numbers 2n = 4x = 40, 2n = 5x = 50, and 2n = 6x = 60 (Delay et al., 1950), and the species is commonly cross-pollinated because of a self-incompatibility mechanism (Hanna and Burton, 1978). Carpetgrass is widely distributed in tropical and subtropical regions (27°N–27°S) and adapted to a wide range of soil pH (pH 4.1–7.1) and soil types (Heath et al., 1985; Liu, 2010). Natural hybrids have provided a very genetically rich germplasm of wild carpetgrass. Previous study revealed that carpetgrass accessions of south China had unique morphological and agronomic traits (Liao et al., 2011). However, the genetic diversity of wild carpetgrass germplasm resources has been rarely explored, especially at the molecular level (Xi et al., 2004a). Thus, the purpose of this study was to assess this variation using molecular markers to advance the genetic breeding of carpetgrass.
Most studies of carpetgrass have focused on its genetic characteristics and resistance (Samarakoon et al., 1990; Smith and Whiteman, 1983; Uddin et al., 2009; Xi et al., 2006), but there is little information regarding its diversity on which to form a complete set of evaluation criteria. The existing studies are limited in the breadth of accessions examined (Xi et al., 2004a). The development of molecular biology has provided popular techniques to assess plant genetic diversity and analyze genetic variation using molecular markers. For lawn grass, analyses by both domestic and foreign scholars have identified a variety of molecular markers that can be applied to these tasks (Wang et al., 2009; Weng et al., 2007; Wu et al., 2006).
To explore genetic characteristics and diversity in plants, many types of molecular markers are available, including restriction fragment length polymorphism (RFLP), random amplified polymorphic DNA (RAPD), amplified fragment length polymorphism (AFLP), sequence-related amplified polymorphism (SRAP), and SSR (SSRs; also known as microsatellites) (Schlotterer, 2004; Weising et al., 2005). RAPD, AFLP, and SRAP are dominant markers that cannot detect whether an allele is heterozygous or homologous. Although RFLPs are codominant, the procedure is complex and requires high-quality DNA, so it is not conducive to automation for a large number of samples (Song et al., 2014). Therefore, SSRs have become the genetic markers of choice for many plant species because of their advantages over RFLPs, RAPDs, AFLPs (Pejic et al., 1998), and other DNA markers, such as intersimple sequence repeats (Wang et al., 2013). The advantages include uniform genome coverage, high polymorphism rates and informativeness, codominance, and the availability of specific polymerized chain reaction (PCR)-based assays. SSRs have been useful for other warm-season turfgrasses (Harris-Shultz et al., 2013; Madesis et al., 2014).
Axonopus has not been previously studied using microsatellite markers, therefore, we examined the genetic diversity of carpetgrass germplasms using SSRs. The results will provide important methods and technologies for future research. The objectives of this study were 1) to use an SSR marker system to study the genetic relationships among 63 carpetgrass accessions from China and 2) to describe the genetic variation in the accessions.
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