In recent years, many improved seeded bermudagrass [Cynodon dactylon (L.) Pers.] cultivars have become commercially available. As the turfgrass quality of several SB cultivars have reached the level of vegetative industry standards (Morris, 2002), the use of SB has increased. With the new focus on improved SB cultivars, germination characteristics have become increasingly important to improve stand establishment and overall turf quality. Bermudagrass can germinate and grow in a wide range of environments from the transition zone to tropical climates (Duble, 1989), and improved SB cultivars continue to be planted across temperate areas in the United States and throughout the world.
Bermudagrass is a warm-season species and optimal growth and development occur during the summer months when favorable temperatures are present. Likewise, germination of SB is also favored when environmental conditions include daytime temperatures of 30 to 35 °C (Sandlin et al., 2006). Dating back to the early 20th century, alternating temperatures of 35 and 22 °C have been used to germinate bermudagrass seed (Bryan, 1918; Harrington, 1923). Although bermudagrass can germinate in daytime temperatures as low as 20 °C and as high as 45 °C, optimal germination has been reported as a daytime/night temperature combination of 30/20 °C (Ahring and Todd, 1978). The positive benefit of alternating temperatures during germination is well established (Steinbauer and Grigsby, 1957) and may be the result of structural changes within the seed that cause a change in the balance between germination inhibitors and promoters (Copeland and McDonald, 2001).
Although irradiance is not an absolute requirement for germination of many species, bermudagrass has improved germination in the presence of light. Morinaga (1926) first established the benefits of irradiance regarding bermudagrass germination by demonstrating how a 24-h photoperiod provided a 56% improvement in germination over seeds in constant darkness. Additionally, Ahring and Todd (1978) successfully performed germination experiments with a photoperiod of 8 h. Currently, the Association of Official Seed Analysts (AOSA) recommends an 8-h photoperiod for all germination studies involving C. dactylon var. dactylon (AOSA, 2009). Bermudagrass plantings in the United States commonly occur between the vernal equinox in March and the autumnal equinox in September. This indicates that photoperiod during a typical planting season exceeds 12 h (Bonan, 2002).
Bryan (1918) first described the difficulty of obtaining adequate germination of bermudagrass seed and demonstrated improved germination results through sulfuric acid treatments. Scarification of the seedcoat by chemical or physical processes can improve imbibition and decrease embryonic inhibitors of germination. Bermudagrass seed has traditionally demonstrated decreased germination, and in recent studies, time to germination varied significantly among cultivars (Patton et al., 2004b; Richardson et al., 2004b). Additionally, in a recent germination study, Sandlin et al. (2006) reported low germination of several cultivars at various temperatures as well as significant differences among cultivars regarding germination.
Seedcoating has been a common practice in many crops but until recently has not been extensively used on turfgrasses. Several coatings have been tested on grass seed germination, including lime (Scott, 1975; Vartha and Clifford, 1973), cytokinin (Greipsson, 1999), fungicides (Newell et al., 1999; Richardson and Hignight, 2010), fertilizer (Bruneau et al., 1989), talc (Scott, 1975), and starch-based polymers (Leinauer et al., 2010; Richardson and Hignight, 2010) to varying levels of success. Reports on bermudagrass seedcoating are rare. Published reports show either no benefit from coating bermudagrass seed (Leinauer et al., 2010; Serena et al., 2012) or reduced germination from seedcoated with fertilizer (Hickey and Engleke, 1983). No research was found that tested the effect of commercially applied seedcoatings on bermudagrass germination.
Two major hypotheses have been put forth concerning differences in SB germination between cultivars: 1) genetic differences; 2) seed preparation such as seedcoatings; or 3) a combination of the two. Currently, improved SB cultivars are available almost exclusively with a commercially applied seedcoating of various materials depending on the seed producer. Although it is known that seedcoatings improve ease of planting and seed supply demands while decreasing planting rate error (Kaufman, 1991), it is not well established whether seedcoatings influence bermudagrass germination. Thus, the objectives of this study were to 1) compare germination percentages of five SB cultivars; 2) evaluate the effect of various temperature regimes on germination of five SB cultivars; and 3) determine whether seedcoating influences germination. Because germination and stand establishment are key factors in selecting a SB cultivar, elucidating a cultivar-specific optimal temperature regime for germination, establishing effects of a seedcoating on germination, and identifying cultivars with increased germination potential should provide valuable information to turfgrass managers.
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