Quantitative Trait Loci (QTL) Analysis of Freezing Tolerance in Zoysiagrass.

Zoysiagrasses (Zoysia japonica Steud. and Zoysia matrella (L.) Merr. 2n=4X=40) are warm-season turfgrasses well-adapted for the southern and transition zones of the United States.  The use of zoysiagrasses is limited to warmer climates because of their relative lack of freezing tolerance compared to cool-season grasses.  Molecular markers associated with this trait would be useful for effective selection of freezing tolerant zoysiagrass lines before field testing. A mapping population was developed from the cross of cold-tolerant ‘Meyer’ with cold-susceptible ‘Victoria’.  In 2014, the 175 progeny of this cross and nine controls were planted in three replications in a randomized complete block design (RCBD) in Laurel Springs, NC, and West Lafayette, IN. Winter survival data was taken in spring 2015 and 2016 with significant variation in winter injury within the population, including six lines that outperformed Meyer across both locations.  Additionally, 125 SSR markers and 1,262 GBS-derived SNPs were used to construct a linkage map in this population. The map covers the expected 20 linkage groups for the zoysia allotetraploid genome.  This map will be used in conjunction with winter injury data from 2015 and 2016 to locate quantitative trait loci (QTL) associated with freezing tolerance and possibly linked markers that could be used for marker assisted selection.