A SNP-based high-density linkage map of zoysiagrass (Zoysia japonica Steud.) and its use for the identification of QTL associated with winter hardiness

Zoysia japonica Steud. (2n = 4x = 40) is a C-4 turfgrass well-adapted for the warm-humid and transitional climatic zones of the USA. Its use is limited to warmer climates because of a relative lack of winter hardiness compared to C-3 grasses. Molecular markers associated with this trait would be useful for effective selection of winter hardy germplasm before field testing. A pseudo-F-2 mapping population of 175 individuals was developed from crosses between Z. japonica cultivars Meyer (freeze-tolerant) and Victoria (freeze-susceptible) and used to generate a high-density genetic map of 104 SSR markers and 2359 sequencing-derived SNP markers. The map covers 324 Mbp and 2520 cM as well as the 20 chromosomes for the zoysiagrass haploid genome. Phenotypic data on winter injury, establishment, and turf quality collected in North Carolina and Indiana in 20142016 were used in conjunction with this map to identify quantitative trait loci (QTL) associated with winter hardiness. Fifty-six QTL associated with winter injury, establishment, and turf quality were identified over six environments. Twelve of those were identified in two or more environments. Furthermore, seven regions of interest were identified on chromosomes 8, 11, and 13 where co-location of QTL for three or more traits occurred. Within these regions, analysis with NCBI basic local alignment search tool (BLAST) identified proteins related to cold and other abiotic stresses tolerance. These QTL and associated markers could be valuable in implementing marker-assisted selection for winter hardiness in zoysiagrass breeding programs.