Genetic maps serve many practical biological purposes and are a key tool in both classical genetic and modern genomic research. Generally, two factors need to be considered in selecting appreciate parental lines to begin the development of mapping populations: 1) DNA polymorphism; 2) hybrid fertility (Xu 2010). A good segregating population is required for the construction of a genetic map. Being a species of wind-facilitated cross-pollination and strong genetic self-incompatibility, switchgrass is an allogamous species (Taliaferro and Hopkins 1996; Casler et al. 2011). Theoretically, every plant in switchgrass is heterozygous in many loci and homozygous in other loci. Switchgrass homozygous inbreds are unavailable in nature. Therefore, crossing of two heterozygous parents would produce a pseudo-F1 population, which often displays substantial segregations. Some loci may have four different alleles between the crossing parents, generating four genotype classes in the progeny. Many others may either follow the F2 pattern in a 1:2:1 ratio (called intercross loci) or the backcross pattern in a 1:1 ratio (called testcross loci) (Lu et al. 2004). Using the testcross markers, i. e., those that are segregating in one parent but not in the other, a

so-called "pseudo-testcross" strategy was proposed for linkage mapping in a controlled cross between two outbred parents (Grattapaglia and Sederoff 1994).

Although it only makes use of a portion of markers from the genome, "pseudo-testcross" strategy provides a simple way for genetic mapping of outcrossing species and has been utilized in practical mapping projects for switchgrass (Missaoui et al. 2005b; Okada et al. 2010). The population of Missaoui et al. (2005b) was composed of 85 full-sib progeny from a cross of ‘Alamo’ genotype AP13 (seed parent) and ‘Summer’ VS 16, whereas the population of Okada et al. (2010) consisted of 238 full-sib plants derived from crossing one genotype (seed parent) of ‘Kanlow’ with a selection of ‘Alamo’. Because male and female meioses in the full-sib populations were distinct and independent processes, two separate parental maps were constructed, one map for the male parent and another for the female parent (Okada et al. 2010).

Recently a self-compatible lowland switchgrass genotype ‘NL 94 LYE 16 x 13’ was identified. A first (S1) generation inbred population from selfing ‘NL 94 LYE 16 x 13’ was developed with the assistance of marker — based identification (Liu and Wu 2012a). This S1 population is similar to an F2 population derived from selfing a F1 hybrid of a cross between two different inbred lines; therefore, only one map was constructed instead of two separate (male and female) maps (Liu et al. 2012).