Significant Variations in Redox and Water Homeostasis Are Associated with Differential Drought Tolerance Between Two Hybrid Bermudagrass Genotypes

Warm-season hybrid bermudagrass is widely used in landscaping and sports turf worldwide for its strong drought tolerance and low growth habit. Breeding new drought-tolerant, high-quality turf-type varieties is crucial to minimize management costs and support sustainable urban development. This study investigated differential drought tolerance between Tifdwarf and the newly released Chuannong-3 cultivar which has high turf quality, focusing on changes in water balance, antioxidant capacity, and transcriptional regulation. The results showed that Chuannong-3 exhibited superior drought tolerance and turf performance compared with Tifdwarf, as evidenced by higher relative water content and osmotic adjustment (OA), reduced oxidative damage, greater photochemical efficiency, and higher chlorophyll content in both leaves and stolons during the 15-day drought stress. In response to a prolonged drought, both Chuannong-3 and Tifdwarf significantly increased activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX), as well as the accumulation of ascorbic acid (ASA) and reduced glutathione (GSH) to mitigate drought-induced oxidative damage. Compared with Tifdwarf, Chuannong-3 showed stronger antioxidant capacity by maintaining higher activities of SOD, CAT, and APX, contents of ASA and GSH, and the ASA/DHA ratio in leaves and stolons, thereby supporting redox equilibrium under drought stress. Additionally, both genotypes showed enhanced accumulation of soluble sugars, proline, and γ-aminobutyric acid, as well as stress-responsive defense gene expression, in response to drought stress. More importantly, the superior drought tolerance of Chuannong-3 was linked to a more robust capacity for OA and metabolic homeostasis than that of Tifdwarf under drought conditions. This was associated with more pronounced upregulation of sugar and amino acid metabolism (soluble sugars, proline, GABA, CdWRKY2, CdERF1, and CdSPS1) and stress-defensive protein biosynthesis (CdABF1, CdDHN4, CdLEA3, CdOSMOTIN, and CdISCS) in Chuannong-3. Taken together, Chuannong-3 is a promising cultivar for cultivation in water-scarce regions. The differences in physiological and molecular mechanisms of drought tolerance between Chuannong-3 and Tifdwarf provide valuable insights for molecular breeding of drought-tolerant bermudagrass.