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Effects of Gibberellic Acid on the CO₂ Exchange Rates of Bermudagrass and St. Augustinegrass when Exposed to Chilling Temperatures¹

This study was conducted to determine if a relationship exists between chilling injury and carbon dioxide exchange rate (CER) of two warm-season turfgrasses, and also to see how the relationship is influenced by exogenously applied gibberellic acid (GA₃). The CER ‘Ormond’ (chill tolerant) and ‘Pee Dee’ (chill sensitlve) bermudagrass [Cynodon dactylon (L.) Pers] and ‘Floratam’ (chill tolerant) and ‘Texas Common’ (chill sensitive) St. Augustlnegrass [Stenotaphrum secundatum (Walt.) Kuntze] were monitored continuously for 14 days chilling temperatures (day/nlght, 7/5 C, respectively). Ormond, Pee Dee, Texas Common, and Floratam showed reductions of 54, 68, 79, and 84% respectively, in daytime CER during the initial chilling photoperiod. Both bermudagrass cultivars showed a significant increase and Floratam a significant decrease in daytime CER 10 hours after GA₃ application. Texas Common did not respond. After 2 weeks of chilling stress, Ormond exhibited a significantly higher percentage of the prechill daytime carbon dioxide exchange rate (PCER) than Pee Dee, Texas Common, and Floratam. Ormond and Pee Dee treated with GA₃ had significantly higher daytime PCER than nontreated Ormond and Pee Dee, as well as treated and nontreated Texas Common and Floratam. All treatments showed a rapid and continual reducton in nighttime CER with increased chilling exposure.

Key Words: Winter dormancy • Low temperature discoloration • Chilling injury • Cynodon dactylon • Stenotaphrum secundatum

² Former graduate research assistant (now assistant professor, Dep. of Agronomy, Univ. of Georgia, Athens, GA, 30602) and professor, Dep. of Crop and Soil Sciences, Texas A & M Univ., College Station, TX, 77843.

Received for publication June 17, 1981.