A bermudagrass variant exhibits strong tolerance to low temperature associated with enhanced sugar metabolism and cold-responsive pathways

As a warm-season turfgrass, bermudagrass (Cynodon) is sensitive to low ambient temperature. The objectives of this study were to evaluate cold tolerance of a new variant Chuannong-3 under field condition and to further elucidate metabolic and molecular bases of cold tolerance in the Chuannong-3 as compared to triploid Tifdwarf (Cynodon transvaalensis x Cynodon dactylon) and tetraploid common bermudagrass 001 (C. dactylon). The Chuannong-3 was identified as a triploid bermudagrass based on ploidy analysis. Chuannong-3, Tifdwarf, or common bermudagrass 001 exhibited different tolerance to low temperature in field (Chuannong-3 > common bermudagrass 001 > Tifdwarf). The Chuannong-3 maintained significantly lower oxidative damage to cell membrane system, chlorophyll loss, and inhibition of photochemical efficiency as well as higher water-soluble carbohydrate content than Tifdwarf or common bermudagrass 001 in winter of 2022 and 2021. Further study found that Chunanong-3 exhibited the highest glucose, fructose, sucrose, raffinose content, raffinose synthase activity, and CdSPS1 expression as compared to Tifdwarf and common bermudagrass 001, which provided potential protection against chilling and freezing damages. Chilling and freezing stresses significantly up-regulated ABA-dependent (endogenous ABA level, CdABF1, CdDHN4, and CdLEA3) and ABA-independent (CdWRKY2, CdCBF1, and CdCOR440) pathways in three bermudagrasses, but the most pronounced effects were detected in the Chuannong-3. These findings indicated that Chuannong-3 had better ability to acclimate to low temperature stress in relation to up-regulation of sugar accumulation and metabolism, ABA signaling, and CBF-COR pathway. This new variant Chuannong-3 could be a valuable bermudagrass grown in temperate and transition zones.