Freeze Tests in St. Augustinegrass: Evaluation of Acclimation Effects.

The adaptation of St. Augustinegrass (Stenotaphrum secundatum [Walt.] Kuntze) in the transitional climatic zone is marginal due to a lack of sufficient winter hardiness. Lab-based freeze tolerance testing not only afford plant breeders a reliable method for evaluating freeze tolerance, they also provide the ability to investigate different underlying mechanisms. The objective of this research was to evaluate the effects of cold-acclimation and deacclimation across two freezing temperatures on nine St. Augustinegrass cultivars. Results indicate that recovery measurements provide the best mean separation for cultivar response and more specifically, recovery at -4°C identifies the best separation of freeze-tolerant cultivars from the intermediate and least tolerant cultivars. This research indicates that cold-acclimation plays a crucial role in the improvement of winter survivability of St. Augustinegrass. A significant loss of freeze tolerance was also identified when plants were subjected to deacclimation events and suggests that St. Augustinegrass can be negatively affected by rapid temperature changes in the transition zone leading to winterkill damage. Accounting for all levels of acclimation provided excellent cultivar separation at both freezing temperatures (-3 and -4 °C) and supports the hypothesis that the inclusion of different acclimation response traits offers the best overall assessment of freeze tolerance in St. Augustinegrass. Overall, this study provides unique information on the effects of cold-acclimation and deacclimation and the complex mechanisms underlying freeze tolerance in St. Augustinegrass.