Water scarcity is one of the major long-term problems that the turf industry faces worldwide, and the use of water on commercial and residential turf is increasingly regulated at national and regional levels. Both chronic shortages of water that occur in arid and semiarid zones (Eriyagama et al., 2009) and occasional extended droughts in humid regions (Carrow, 1996b) can increase the need to irrigate turf and pose challenges to maintain acceptable turfgrass quality. Drought avoidance refers to the plant’s ability to increase water uptake by developing a deep, extensive, and viable root system; and to reduce water loss through stomatal control (Huang, 2008; Huang et al., 1997a, 1997b).
Determining genetic potential in various root traits that are associated with drought mechanisms is an important screening process for developing turfgrasses with good drought response. Root length density (RLD, cm root cm−3 soil), has been widely used to quantify the extensiveness of the roots (Carrow, 1996a; Miller and McCarty, 1998), and is generally positively correlated with the rate of water uptake under well-watered conditions (Huang, 2000). Variations of RLD in a limited number of turfgrass species including cool-season and warm-season grasses have been documented. For example, Qian et al. (1997) reported that total root length in a 120-cm profile of ‘Mustang’ tall fescue (Festuca arundinaceae Schreb) was three times greater than ‘Meyer’ zoysiagrass (ZJ), ‘Midlawn’ hybrid bermudagrass [C. dactylon (L.) Pers. var. dactylon], and ‘Prairie’ buffalograss [Buchloe dactyloides (Nutt.) Engelm.] when grown in a greenhouse in calcined clay. This study was in accordance with Carrow (1996b), who documented similar results when comparing RLD between zoysiagrass and tall fescue.
However, high RLD alone does not translate to good performance during drought. In fact, high RLD in the surface soil would result in faster depletion of water and early onset of drought stress (Su et al., 2008). Profile characteristics of roots and associated drought avoidance mechanisms have been reported in several studies (Burton et al., 1954; Carrow, 1996b; Qian et al., 1997; Sheffer et al., 1987). Carrow (1996b), reported that high RLD close to the soil surface (3–10 cm) was related to greater leaf firing, while high RLD in the 20–60-cm horizon was associated with less leaf firing and wilting in tall fescue cultivars during drought.
The rate of root depth development (RRDD, cm/d) has been used as a potential criterion for selecting drought-resistant plants (Hamblin and Tennant, 1987). Root penetration of warm-season grasses (Burton et al., 1954) and rooting depth of 25 zoysiagrass cultivars (Marcum et al., 1995) were found to be correlated with drought response. Plants with rapid root extension were expected to develop deep roots, and the narrow-sense heritability of root extension in creeping bentgrass (Agrostis stolonifera L.) was high when grown in flexible root tubes (Lehman and Engelke, 1991). Acuña et al. (2010) developed a screening technique to evaluate bahiagrass (Paspalum notatum Flüggé) germplasm for RRDD, and a linear increase of root depth was reported. This technique can be potentially used to screen other turfgrass species for their root development.
Rooting patterns under well-watered conditions may not translate to rooting patterns under drought (Huang, 1999); however, the ability to develop deep and extensive root systems under well-watered conditions may ensure access to moisture deeper in the soil profile at the onset of drought. Correlations have been documented between rooting characteristics under well-watered conditions and survival under deficit irrigation in zoysiagrass (Marcum et al., 1995).
Common bermudagrass and zoysiagrass are widely used as warm-season turfgrass species in the southern United States for landscapes and sport fields (Trenholm et al., 2000; Unruh et al., 2013). African bermudagrass, indigenous to the Transvaal region of South Africa (De Wet and Harlan, 1971), has been used for turf (Juska and Hanson, 1964) and as a parent to produce interspecific bermudagrass hybrids (Burton, 1991; Kenworthy et al., 2006). There is no available information related to rooting traits in African bermudagrass.
The objectives of this study were to 1) determine RRDD and root profile characteristics of two bermudagrass species and two zoysiagrass species, 2) identify genotypes with great RRDD and high RLD in the lower profile. Both experimental lines and commercial cultivars were included in the study.
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