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Title: Freeze-Testing in St. Augustinegrass I: Evaluation methods

item KIMBALL, JENNIFER - North Carolina State University
item Tuong, Tan
item ARELLANO, CONSUELO - North Carolina State University
item Livingston, David
item MILLA-LEWIS, SUSANA - North Carolina State University

Submitted to: European Journal of Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/19/2017
Publication Date: 7/25/2017
Citation: Kimball, J., Tuong, T.D., Arellano, C., Livingston, D.P., Milla-Lewis, S.R. 2017. Freeze-Testing in St. Augustinegrass I: Evaluation methods. European Journal of Agronomy. 213:110-115.

Interpretive Summary: St Augustinegrass is an excellent choice for homeowners lawns because of its excellent drought and shade tolerance. However, freezing tolerance of St Augustinegrass is very poor and new methods of screening existing genotypes will help to make this species a viable option in more northerly areas. In this study acclimation to freezing temperatures, which occurs in the fall, as well as de-acclimation, which can occur as temperatures undergo prolonged warming during winter, were studied. Nine genotypes were evaluated and it was determined that -4°C was the optimal freeze test temperature to identify superior genotypes. Differences between the 9 genotypes for the degree to which they will de-acclimate were also investigated. This study provides information on the complexity of freezing tolerance during winter months for this important turf grass species.

Technical Abstract: The adaptation of St. Augustinegrass (Stenotaphrum secundatum [Walt.] Kuntze) in the transitional climatic zone is marginal due to a lack of sufficient winter survival. Lab-based freeze tolerance testing method 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 genotypes. Results indicate that recovery measurements provide the best mean separation for genotype response and more specifically, recovery at -4°C identifies the best separation of freeze-tolerant genotypes from the intermediate and least tolerant genotypes. Accounting for all levels of acclimation provided excellent genotype 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. 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 suggesting that St. Augustinegrass can be negatively affected by rapid temperature changes in the transitional climatic zone leading to increased sensitivity to winterkill. Overall, this study provides unique information regarding the effects of cold acclimation and deacclimation and the complex relationships within and between mechanisms underlying freeze tolerance in St. Augustinegrass.