Response of Twenty Tall Fescue (Schedonorus arundinaceus (Schreb.) Dumort.) Cultivars to Low Mowing Height

Tall fescue (Schedonorus arundinaceus (Schreb.) Dumort.) is the most widely used species in the European transition zone, however, despite its good wear tolerance, its use is still limited to lawns and landscape areas due to concerns about its ability to withstand low mowing regimes. A two years field study was conducted to access performance of twenty tall fescue cultivars (‘Ares’, ‘Armani’, ‘Dynamites LS’, ‘Firecracker SLS’, ‘Firewall’, ‘Foxhound’ ‘Granditte’, ‘JT-LT2′, ‘JT-338′, ‘Karakum’, ‘Lexington’, ‘Olympic Gold’, ‘Rebounder’, ‘Rhambler SRP’, ‘Starlett’, ‘Supersonic’, ‘Talladega’, ‘Thunderstruck’, ‘Titanium 2LS’, ‘Turfway’) mowed weekly at 18 mm. Turfgrass was evaluated every two weeks for visual quality, color, density, texture and uniformity, as well as percent green cover (PGC) and dark green color index (DGCI), and normalized difference vegetation index (NDVI), and traction twice per year. Although no cultivars showed sufficient quality throughout the year, ‘Turfway’, ‘Titanium 2LS’ and ‘JT-338’ achieved high quality rating during spring and fall, the two seasons with the highest frequency of games played on sports field in northern Italy. Traction ratings collected in these study fell within acceptable range for football fields. Our results suggest that improved dwarf-type tall fescue cultivars can be used in sport fields in Northern Italy.

Deletion in the Promoter of PcPIN-L Affects the Polar Auxin Transport in Dwarf Pear (Pyrus communis L.)

Dwarf cultivars or dwarfing rootstocks enable high-density planting and are therefore highly desirable in modern pear production. Previously, we found that the dwarf growth habit of pear is controlled by a single dominant gene PcDw. In this study, PcPIN-L (PCP021016) was cloned from dwarf-type and standard-type pears. PcPIN-L expression was significantly lower in the dwarf-type pears than in standard-type pears, which was caused by the CT repeat deletion in the promoter of dwarf-type pears. PcPIN-L overexpression in tobacco plants enhanced the growth of the stems and the roots. Notably, the indole acetic acid (IAA) content decreased in the shoot tips and increased in the stems of transgenic lines compared with wild type, which is consistent with the greater IAA content in the shoot tips and lower IAA content in the stems of dwarf-type pears than in standard-type pears. The CT repeat deletion in the promoter that causes a decrease in promoter activity is associated with lower PcPIN-L expression in the dwarf-type pears, which might limit the polar auxin transport and in turn result in the dwarf phenotype. Taken together, the results provide a novel dwarfing molecular mechanism in perennial woody plants.

A Gamma-ray–Induced Dwarf Mutant from Seeded Bermudagrass and Its Physiological Responses to Drought Stress

Breeding for dwarf-type bermudagrass (Cynodon dactylon) with enhanced drought resistance is important for producing quality turf with reduced irrigation. A dwarf-type mutant (S-20–1) that exhibits slower vertical growth, and shorter internodes and leaf length was selected from the gamma-ray–irradiated seeds of a bermudagrass cultivar Sundevil II (S-CK). S-20–1 had slower turf coverage than S-CK. Compared with S-CK, the vertical growth of S-20–1 was more promoted by gibberellin (GA3) treatment. S-20–1 showed an enhanced drought resistance in greenhouse and field tests. Under drought stress, S-20–1 maintained higher relative water content and lower levels of ion leakage, malondialdehyde, and leaf firing than S-CK. Antioxidant enzyme activities and antioxidant content showed no difference between S-20–1 and S-CK under well-watered conditions, while higher enzyme activities were maintained in S-20–1 under drought stress. Free proline accumulated in response to drought stress and showed a positive correlation to the increased ion leakage, while S-20–1 had lower levels than S-CK. Our results indicated that the dwarfism in S-20–1 induced by gamma-ray irradiation might be the result of less GA3 or decrease of sensitivity to GA3 in the mutant. The improved drought resistance of the mutant is associated with maintenance of higher levels of antioxidant enzyme activities. More accumulation of proline in S-CK than S-20–1 reflected a physiological response to the drought-induced injury rather than an association with drought resistance of S-20–1.

Dwarf Bermudagrass Tolerance to Preemergence Herbicides

Preemergence herbicides are applied to prevent summer annual weed infestations in turf, but safety to dwarf-type bermudagrass golf greens has not been determined for many of these materials. Field experiments tested ‘TifEagle’ bermudagrass response to bensulide at 11.2 kg·ha−1 (a.i.), dithiopyr at 0.56 kg·ha−1 (a.i.), napropamide at 2.2 kg·ha−1 (a.i.), oxadiazon at 2.2 kg·ha−1 (a.i.), oxadiazon plus bensulide at 1.7 + 6.7 kg·ha−1 (a.i.), and pendimethalin at 1.7 kg·ha−1 (a.i.). All herbicides reduced root mass from the nontreated, but only losses incited by oxadiazon plus bensulide were acceptable (less than 20%). Dithiopyr, napropamide, and pendimethalin delayed spring greenup in 2003 and 2004, whereas oxadiazon plus bensulide delayed spring greenup in 2004. In greenhouse experiments, ‘TifEagle’ bermudagrass root mass was reduced 19% to 37%, 30% to 33%, 4% to 26%, 28% to 37%, and 24% to 30% from various rates of bensulide, dithiopyr, napropamide, and pendimethalin, respectively. Oxadiazon and oxadiaxon plus bensulide reduced root mass by only 2% to 15% and 15% to 22%, respectively. In another experiment, oxadiazon plus bensulide at 1.7 + 6.7 kg·ha−1 did not injure shoots or roots of ‘Champion’, ‘FloraDwarf’, ‘MiniVerde’, ‘Tifdwarf’, or ‘TifEagle’ bermudagrass. Overall, dwarf-type bermudagrass golf greens do not appear to tolerate mitotic inhibitor preemergence herbicides, whereas oxadiazon or oxadiazon plus bensulide caused minimal injury.

Dwarf Bermudagrass Responses to Flurprimidol and Paclobutrazol

Plant growth regulators are applied to inhibit uneven shoot growth of putting green turf but research is limited on responses of dwarf-type bermudagrass cultivars to growth inhibition. Experiments were conducted at the Clemson University Greenhouse Complex with `Champion' and `TifEagle' bermudagrass grown in polyvinylchloride containers with 40 cm depths and 177 cm2 areas built to United States Golf Association specification. Flurprimidol was applied at 0.14, 0.28, and 0.48 kg·ha–1 a.i. and paclobutrazol at 0.14 kg·ha–1 a.i. on separate containers. Flurprimidol at 0.28 and 0.42 kg·ha-1 caused 17% and 31% reduction in turf color 5 weeks after treatment (WAT), respectively. `Champion' exhibited unacceptable turf injury (>30%) 2 WAT from paclobutrazol and all flurprimidol rates. `TifEagle' had unacceptable turf injury from flurprimidol at 0.42 kg·ha–1 2 WAT, 0.28 kg·ha–1 3 WAT, and 0.14 kg·ha–1 4 WAT that did not recover. Moderate injury (16% to 30%) was observed from paclobutrazol on `TifEagle' but ratings were acceptable. After 6 weeks, flurprimidol at 0.14, 0.28, and 0.42 kg·ha–1 reduced bermudagrass green shoot density (GSD) per square centimeter by 20%, 40%, and 40%, respectively, while paclobutrazol reduced GSD 12%. `TifEagle' total clipping yield was reduced 60%, 76%, and 86% from flurprimidol at 0.14, 0.28, and 0.42 kg·ha–1, respectively, and 37% from paclobutrazol. `Champion' total clipping yield was reduced 82%, 90%, and 90% from flurprimidol at 0.14, 0.28, and 0.42 kg·ha–1, respectively, and 58% from paclobutrazol. After 6 weeks, flurprimidol reduced `Champion' total root mass by 44% over all three rates. `Champion' treated with paclobutrazol had similar total root mass to the untreated. `TifEagle' treated with all PGRs had similar rooting to the untreated. Overall, flurprimidol will likely not be suitable for dwarf bermudagrass maintenance at these rates; however paclobutrazol may have potential at ≤0.14 kg·ha–1. Chemical names used: Flurprimidol {α-(1-methylethyl)-α-[4-(trifluoro-methoxy) phenyl] 5-pyrimidine-methanol}; Paclobutrazol, (+/-)–(R*,R*)-β-[(4-chlorophenyl) methyl]-α-(1, 1-dimethyl)-1H-1,2,4,-triazole-1-ethanol.

Response of Six Dwarf-type Bermudagrasses to Trinexapac-ethyl

Trinexapac-ethyl (TE) is an effective plant growth retardant for hybrid bermudagrass; however, growth responses of various dwarf-type bermudagrass cultivars to TE have not been reported. Two 60-day greenhouse experiments were conducted at the Clemson Greenhouse Research Complex, Clemson, S.C., to evaluate the response of `Champion', `FloraDwarf', `MiniVerde', `MS Supreme', `Tifdwarf', and `TifEagle' bermudagrass with and without TE at 0.0125 kg·ha-1 a.i. per 10 days. From 20 to 60 days after initial treatments, TE enhanced visual quality 9% to 13% for all cultivars. From four samples, TE reduced clippings 63%, 63%, 69%, 62%, 64%, and 46% for `Champion', `FloraDwarf', `MiniVerde', `Tifdwarf', and `TifEagle', respectively. Trinexapac-ethyl enhanced root mass 23% and 27% for `MiniVerde' and `FloraDwarf' bermudagrass, respectively. `Champion', `MS Supreme', `Tifdwarf', and `TifEagle' bermudagrass treated with TE had similar root mass to the untreated respective cultivars. Among untreated cultivars, `FloraDwarf', `MiniVerde', `MS Supreme', and `Tifdwarf' had similar root masses; however compared to these cultivars, `Champion' and `TifEagle' had 33% and 81% less root mass, respectively. Root length was unaffected by TE; however, `Champion' and `TifEagle' averaged 20% and 36% less root length compared to `Tifdwarf' bermudagrass, respectively, while `FloraDwarf', `MiniVerde', and `MS Supreme' had similar root length to `Tifdwarf'. Trinexapac-ethyl safely enhanced turf quality and reduced clipping yield at 0.0125 kg·ha-1 per 10 days without inhibiting root growth of six dwarf-type bermudagrasses. Chemical name used: [4-(cyclopropyl-[α]-hydroxymethylene)-3,5-dioxo-cyclohexane carboxylic acid ethyl ester] (trinexapac-ethyl).