Shade stress is a problem affecting the quality of an estimated 20% to 25% of all turfs (Beard, 1973; Dudeck and Peacock, 1992). Shading reduces incident solar radiation and alters the microclimate in which the turf grows (Beard, 1997). Turfgrass grown under shade suffers from reduced photosynthesis (Dudeck and Peacock, 1992; Qian et al., 1998), lower carbohydrate reserves (Atkinson et al., 2012; Bell and Danneberger, 1999; Burton et al., 1959; Qian et al., 1998), and reduced tillering (Ervin et al., 2002; Okeyo et al., 2011a; Qian et al., 1998). As a result, turfgrass grown under shade often declines in quality.
Zoysiagrass is a sod-forming warm-season perennial turfgrass indigenous to the Pacific Rim (Anderson, 2000). There are 11 species in the Zoysia genus, of which three are used as a turfgrass: Z. japonica, Z. matrella, and Z. pacifica (Engelke and Anderson, 2003). In the United States, zoysiagrass is used extensively on golf courses and home lawns throughout the transition zone. The lower input requirements of zoysiagrass compared with other available turfgrasses make it a desirable choice for use as a turfgrass in this region (Fry and Huang, 2004).
Zoysiagrasses vary in shade tolerance. In general, Z. matrella cultivars and ‘Emerald’ are considered more shade-tolerant than Z. japonica cultivars (Fry and Huang, 2004; Okeyo et al., 2011a; Sladek et al., 2009; Wherley et al., 2011). ‘Meyer’ has been the primary zoysiagrass used in the transition zone since its release in 1951, mainly as a result of its excellent cold-hardiness (Grau and Radko, 1951). However, ‘Meyer’ performs poorly under moderate to dense shade (Ervin et al., 2002; Riffell et al., 1995; Sladek et al., 2009). This is problematic on golf courses and home lawns with considerable shade. Often, ‘Meyer’ is replaced with Z. matrella cultivars or ‘Emerald’, which are less hardy (Fry and Huang, 2004), and can only be used in the southern-most part of the transition zone.
Since 2004, researchers at Kansas State University (Manhattan, KS) and Texas A&M University (Texas AgriLife Research and Extension Center, Dallas, TX) have collaborated to develop zoysiagrass cultivars with excellent quality and freeze tolerance. In an effort to produce improved zoysiagrasses, researchers crossed lines of (Z. japonica × Z. pacifica) and Z. matrella with Z. japonica lines. Their goal was to develop cultivars with excellent density and a fine leaf texture like that of Z. matrella but with freezing tolerance equal to or better than that of ‘Meyer’. Over 600 progeny from the aforementioned crosses have been evaluated for quality and winter survival at the Rocky Ford Turfgrass Research Center at Manhattan, KS (Fry et al., 2008; Okeyo et al., 2011b). Evaluation of several of these grasses indicated that progeny from (Z. matrella × Z. japonica) and [(Z. japonica × Z. pacifica) × Z. japonica] exhibited superior stolon production under natural shade compared with ‘Meyer’ (Okeyo et al., 2011a) and have a freezing tolerance equal to that of ‘Meyer’ (Okeyo et al., 2011b).
The long-term shade tolerance of these high-performing progeny has not been evaluated. Identifying genotypes with improved shade tolerance compared with ‘Meyer’ and characteristics aiding survival under dense shade will help lead to improved zoysiagrasses for the transition zone. This study was conducted to determine changes and differences in growth among selected Zoysia cultivars and progeny under a natural shade environment over a 3-year period in the transition zone.
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