Genome-wide association studies (GWAS) for germination efficiency, drought resistance, and growth traits in common bermudagrass

Common bermudagrass [Cynodon dactylon (L.) Pers. var. dactylon] is a vital warm-season perennial grass species with great economic and ecological values for use as turf, forage, and soil conservation and remediation. Seeding offers significant economic advantages over vegetative propagation for establishing bermudagrass. However, the adoption of seeded cultivars is limited by slow germination speed and low germination rates. In addition, adaptive traits such as establishment rate, winter hardiness, and drought resistance are key targets for breeders seeking to improve bermudagrass performance. However, the molecular resources necessary to develop improved and resilient seeded bermudagrass cultivars remain underexplored. Accordingly, the objectives of this study were to quantify genetic variance and to identify genetic variants controlling germination efficiency, establishment rate, winter hardiness, and drought resistance. A diverse panel of 216 genotypes was formed for genome-wide association studies (GWAS). Seed germination traits (germination potential, rate, final percentage) were phenotyped over two runs in a randomized complete block design (RCBD) with three replications. Field evaluation for establishment rate, spring green-up, and drought response traits were conducted in a replicated field trial with RCBD over two seasons (2023 and 2024) in Stillwater, OK. Substantial phenotypic and genetic variation were observed across traits, with reliability estimates for germination traits ranged from low to high (0.23-0.82), the reliability estimate for establishment rate was high (0.64), the estimate for spring green-up was moderate (0.55), and the estimates for drought response traits ranged from low to high (0.12-0.63). The panel was sequenced, and 21,810 high quality single nucleotide polymorphisms (SNPs) were used for association mapping. GWAS identified 38 marker-trait associations (MTAs) for germination traits, 23 MTAs for establishment rate, 13 MTAs for spring green-up and 28 MTAs for drought response traits, accounting for phenotypic variance up to 64.32%. The results of this study add valuable information of genetic mechanisms for germination efficiency, establishment rate, spring green-up and drought resistance, providing specific sequences for marker-assisted breeding to develop new common bermudagrass cultivar with improved germination, establishment, winter hardiness, and drought resistance.