Heat Resistance Enhanced by Trinexapac-Ethyl and Benzyladenine Combination in Creeping Bentgrass

Abstract

Creeping bentgrass (Agrostis stolonifera var. palustrisHuds) is one of the most widely used turfgrasses for golf greens and fairways. The optimum temperature for creeping bentgrass ranges between 15 to 24 C for shoot growth and 10 to 18 C for root growth (Beard, 1973). However, temperatures during summer months often exceed the optimal ranges for prolonged periods. High-temperature stress is one of the major factors limiting use of creeping bentgrass in transitional and warmer climatic regions (Beard, 1997; Beard and Daniel, 1966; Carrow, 1996; Wang et al., 2003). Typically, grasses are exposed to high temperatures more than 35/30 C (day/night) for 20 to 30 d during the summer in many areas of China. Such prolonged high temperatures severely limit shoot and root growth, and survival of plants. Many physiological factors are involved in heat stress injury. Heat stress reduces photosynthesis (Carrow and Duncan, 2003; Paulsen, 1994; Xu and Huang, 2001), and increases respiration, which exhausts carbohydrate reserves (Xu and Huang, 2003). Carbohydrate metabolism is among the key physiological processes controlling plant growth. High-quality turf is often cultivated under a frequent mowing program. Clipping removal is one of the main concerns in reduction of energy reserves and leaf area required for photosynthesis in creeping bentgrass. Trinexapac-ethyl (TE) is a plant growth regulator that inhibits gibberellin (GA) synthesis by blocking the transformation of GA20 to GA1 (Rademacher, 2000). TE reduces vertical growth of many turfgrass species, which results in decreased clipping weights (Fagerness et al., 2004; McCullough et al., 2004, Tegg and Lane, 2004). TE has been shown to reduce sod heating through reducing plant respiration, resulting in enhanced stress resistance in Kentucky bluegrass (Poa pratensis) (Ervin and Koski, 2001a,b; Heckman et al., 2001), indicating its effects on energy conservation from respiratory consumption. Cytokinin, a phytohormone, may regulate plant response to high-temperature stress. A period of heat stress reduced the level of cytokinins in roots in many plants (Itai et al., 1973; Liu et al., 2002; Udomprasert et al., 1995). Application of cytokinins (Liu and Huang, 2002) or products containing cytokinins (Zhang et al., 2003) to the root system or shoot (Zhang and Schmidt, 2000) could enhance the heat resistance of turfgrasses. The positive effects of cytokinins on stress resistance of plants are related to protection from oxidative stress by preventing the formation of free radicals or by the regulation of antioxidant enzyme activities (Caers et al., 1985; Liu and Huang, 2002; Wang et al., 2003; Zhang and Schmidt, 2000). Although many plant growth regulators are commercially available for regulating plant growth and production, few of them have been reported to have positive effects on improving plant heat resistance. Cytokinins and TE are two chemicals that have shown potential beneficial effects for plant heat resistance in previous reports. However, no work has been conducted to determine the interactive effects of TE and 6-benzyladenine (BA). The objectives of this study were to investigate 1) whether a TE and cytokinin combination can enhance heat resistance of creeping bentgrass and 2) the morphological and physiological effects of TE and BA in the regulation of turf summer performance and heat resistance in creeping bentgrass. Materials and Methods