High-Density Genetic Maps of Zoysiagrass Using RAD Markers.

Zoysiagrass, a warm-season grass, has received increased interest due to its low maintenance and excellent tolerance to salt, shade, heat, and cold stress conditions. Zoysia japonica (Japanese lawngrass) is an allotetraploid species with 2n = 40. We constructed high-density genetic maps of Zoysia japonica using restriction site associated DNA (RAD) sequencing approach and an F1 mapping population derived from a cross between Carrizo and  El Toro. A total of 60 F1 individuals were genotyped along with their parents by RAD sequencing with Nsi I and Mse I double-digestion. Two linkage maps were constructed, one for each of the parents. A map consisting of 2,408 RAD markers distributed on 21 linkage groups was constructed for Carrizo. Another map with 1,230 RAD markers mapped on 20 linkage groups was constructed for El Toro.  The average distance between adjacent markers of the two maps was at 0.56 cM and 1.4 cM, respectively. Comparative genomics analysis was carried out between zoysiagrass and sorghum genomes. A total of 446 mapped maternal-derived alleles and 226 mapped paternal-derived alleles matched sorghum gene models. Using sorghum as a reference genome, two homologous chromosomes of each of the 10 Sorghum chromosomes were found in zoysiagrass genome, indicating an allotetraploid origin of zoysiagrass. These high-density genetic maps will be used for genome sequence assembly and mapping quantitative trait locus for large patch disease resistance.