ABSTRACT
Bermudagrass is a warm-season, sod-forming, perennial grass that utilizes the C4 photosynthetic carbonxationpathway(Kranset al.1979).Theoptimumgrowthofbermudagrassplantsoccurs between27°Cand35°C(Turgeon2008).Coldhardinessisamajorlimitingfactordeterminingthe adaptationrangeofbermudagrassasitsuseextendsbeyondtropicalandsubtropicalregions,the primaryadaptationareaforbermudagrass.Useathigherlatitudesresultsinagreaterriskofwinterkill (Taliaferro et al. 2004a). For example, in the United States, bermudagrass has been used in the transitionzonebetweentheprimarycool-seasonturfgrassbeltinthenorthernstatesandprimary warm-seasonturfgrassbeltinthesouthernstates.Althoughnotwelldened,theclimaticallyvariabletransitionzoneiswithintherangeoftheU.S.DepartmentofAgriculture(USDA)planthardinesszones5through7.Someharshwintersinthetransitionzonearesoseverethatbermudagrass stands can be extensively damaged or killed. The costs associated with extended loss of use and investmentsinreestablishmentofbermudagrassaresubstantial(Andersonet al.2005).Fortunately, bermudagrassfreezetoleranceisaheritabletrait,coldhardybermudagrassgermplasmexistsin
33.1 Introduction .......................................................................................................................... 851 33.2Importance and Economic Uses of Bermudagrass ............................................................... 852
33.2.1Forage Grass ............................................................................................................. 852 33.2.2Turfgrass ................................................................................................................... 852
33.3Germplasm Distribution: Endemic and Cosmopolitan Species ........................................... 853 33.4 Development of Cold Hardy Forage and Turf Cultivars ....................................................... 855
33.4.1Forage Bermudagrass Cultivars with Improved Cold Hardiness ............................. 855 33.4.2Turf Bermudagrass Cultivars with Improved Cold Hardiness ................................. 857
33.5Evaluation of Cold Hardiness: Field-Based and Laboratory-Based Methods ...................... 859 33.6Inheritance, Physiological, and Molecular Mechanisms ...................................................... 861 33.7 Future Prospects in Bermudagrass Cold Hardiness Improvement ....................................... 862 References ...................................................................................................................................... 863
nature, and plant breeding is able to genetically incorporate this desirable trait into improved cultivars. Developmentandreleaseofcultivarsimprovedinfreezetolerancereducesthewinterkillriskwhen bermudagrassisusedinthetransitionzoneandextendsitsusetohigherlatitudes.Thischapter addressesthetopicsofeconomicsignicance,germplasmvariability,anddistributionrelatedto coldhardiness,developmentofcultivarswithimprovedcoldhardinessforforageandturfuse, evaluation and determination of freeze tolerance, related physiological and molecular mechanisms, and future potential to continue the improvement of bermudagrass freeze tolerance.
