Identification of quantitative trait loci associated with winter survival in St. Augustinegrass (Stenotaphrum secundatum)

The winter survival of St. Augustinegrass (Stenotaphrum secundatum [Walt.] Kuntze) in the transition zone is constrained by its poor freeze tolerance. A limited understanding of the genetic and physiological mechanisms involved in low-temperature response has hindered progress in breeding for this trait. Identification of quantitative trait loci (QTL) associated with winter survival will enhance the breeding effort for trait improvement via marker-assisted selection (MAS). This study identified QTL for winter survival traits in a mapping population containing 184 lines derived from the self-pollination of freeze-tolerant cultivar 'Raleigh'. Phenotypic data on percent green cover (PGC), UAS-derived PGC (UPGC), fall color, winterkill, and winter injury were collected from three field trials established in 2021, 2022, and 2023. Leaf pigment content (chlorophyll a, chlorophyll b, carotenoids, and anthocyanins) in the fall was also measured through lab assays, but only in the 2023 field trial. A genetic linkage map constructed with 2,212 SNP markers was used for QTL analysis. QTL mapping identified 85 significant QTL, including eight genomic regions overlapping with prior winter survival QTL across chromosomes 1, 2, 3, 6, 8, and 9. Multiple candidate genes associated with low-temperature stress tolerance were discovered within these overlapping regions. These findings provide valuable genomic resources for improving winter survival in St. Augustinegrass through MAS.