Bermudagrass Freezing Tolerance Associated with Abscisic Acid Metabolism and Dehydrin Expression during Cold Acclimation.

Recent advances in common and hybrid bermudagrass (Cynodon spp.) breeding and cultural management practices have enabled its utilization as a sports surface into USDA cold hardiness zones 5 and 6. Use of these more cold-hardy bermudagrass cultivars further into transition- and cool-season zones increases the probability of freezing injury and the need for an improved understanding of physiological responses to chilling and freezing temperatures. This study investigated changes in abscisic acid (ABA) metabolism and dehydrin expression during cold acclimation (CA) and their association with freezing tolerance in bermudagrass. Two cold-sensitive and two cold-tolerant cultivars were either subjected to CA at 8/4 °C (day/night) with a light intensity of 250 µmol m^-2 s^-1 over a 10-h photoperiod for 21 d or maintained at 28/24 ^oC (day/night) with the same light intensity over a 12-h photoperiod. In a separate study, ABA at 0, 50, 100, and 150 µM was applied to Patriot bermudagrass without CA. ABA content in leaf and stolon tissues increased sharply during the first week of CA. Patriot and Riviera (cold tolerant) had greater ABA content and less stolon electrolyte leakage (EL) relative to Tifway and Princess-77 (relatively cold sensitive). When averaged over three sampling dates (7, 14, and 21 d of CA), stolon ABA content was 37.9 for Patriot, 27.5 for Tifway, 32.7 for Riviera, and 13.5 ng g^-1 for Princess. Expression of a 25-kDa dehydrin protein increased during CA in all four cultivars. A significant correlation was found between ABA content and freezing tolerance. Exogenous ABA at 100 and 150 µM significantly increased endogenous ABA content and expression of the 25-kDa dehydrin. The results suggest selection and use of cultivars with rapid accumulation of ABA and certain dehydrins during CA and/or in response to exogenous ABA could improve bermudagrass persistence in transition zone climates.