Traffic tolerance of fine fescues: techniques for screening germplasm

The term fine fescue refers to several Festuca spp. that have a very fine leaf texture compared to most other turfgrass species. These species are adapted to low-input management systems and have been used in mixtures with other cool-season grasses. However, fine fescues are not utilized to the same extent as other species partially due to their poor traffic tolerance and recuperative ability. Improvement in traffic tolerance of fine fescues would enable use of these grasses beyond turf systems that experience little to no traffic. The purpose of this dissertation was to develop and evaluate germplasm screening techniques that improve selecting efficiency for traffic tolerant fine fescues. The specific objectives of this research were: i) to evaluate the effect of traffic form (abrasive wear vs. cleated traffic) and season (spring vs. summer vs. autumn) on the assessment of fine fescue traffic tolerance (Chapters 1 and 2); ii) to evaluate the effect of nitrogen fertilization and harvest time on cell wall composition of fine fescues (Chapters 3 and 4); iii) to investigate the correlation between cell wall composition and wear tolerance of fine fescues; and iv) to develop near-infrared reflectance spectroscopy (NIRS) models to determine the cell wall composition of fine fescues. For the first objective, the ability of fine fescue turf to maintain a dense cover depended on the specific traffic form and varied based on the season during which wear stress occurred. Abrasive wear, applied with Rutgers Wear Simulator, caused more thinning of the turf canopy than cleated traffic applied with the Cady Traffic Simulator. Thus, abrasive wear resulted in a greater separation among fine fescues based on the fullness of turf cover (FTC) and will likely improve selection efficiency compared to cleated traffic. The FTC response of fine fescues were more sensitive to traffic stress during summer because of the high disease pressure and heat stress. Screening for fine fescues for improved traffic tolerance during spring would probably be less biased and more effective at identifying tolerance to traffic within fine fescues because other abiotic or biotic stresses would be avoided or minimized. Abrasive wear was also effective in identifying cultivars that are susceptible to leaf bruising. Leaf bruising was more severe during summer and autumn due to the heat stress. However, leaf bruising response of fine fescue cultivars varied with the season; sheep fescue and strong creeping red fescue were more susceptible to leaf bruising during summer while Chewings fescue and slender creeping red fescue were more bruised during autumn. Thus, evaluation of this characteristic would need to be conducted in both the summer and autumn. For the second objective, N fertilization was expected to alter cell wall composition as it promotes new leafy growth, which would be expected to have lower cell wall content. However, the effect of N fertilization on cell wall composition was not observed. Differences among three fine fescue species were significant and the ranking of total cell wall (TCW) content remained the same throughout the entire study: hard fescue > Chewings fescue > strong creeping red fescue. Harvest time (season) had a significant impact on cell wall composition; TCW content was greater in summer (August) compared to spring (May) and autumn (November). However, the relative ranking among five fine fescue species was consistent despite the fluctuation in concentration caused by the harvest time. The concentrations of TCW, hemicellulose, lignocellulose and cellulose from high to low were: Sheep fescue > hard fescue > Chewings fescue = slender creeping red fescue > strong creeping red fescue. For the third objective, a general pattern between wear tolerance and verdure biomass and cell wall constituents of fine fescues were identified on an inter-specific level; improved wear tolerance was associated with greater verdure biomass, TCW, and lignocellulose content as well as reduced lignin content. Correlations were not as strong on an intra-specific level which is probably due, at least in part, to a narrower range of diversity for these characteristics within each species. The potential to improve wear tolerance by selecting for greater verdure biomass, TCW and lignocellulose contents appeared to be more promising for Chewings and strong creeping red fescues than hard fescue. For the fourth objective, NIRS provided a relatively rapid and precise method of estimating total N (R2cal > 0.93) in the verdure at both the inter- and intra-specific levels. Due to the complexity of the constituents, the prediction accuracy was less favorable, but reliable, for TCW (R2cal > 0.70), lignocellulose (R2cal > 0.78) and hemicellulose (R2cal > 0.79) at the intra or inter specific level(s). Further development of these NIRS prediction models would facilitate future research that defines the correlation between cell constituents, such as total N and cell wall composition, and the traffic tolerance of fine fescues. This research advanced our understanding of methods to assess the traffic tolerance of fine fescues. Screening efficacy and accuracy can be improved using abrasive wear during spring when confounding stresses are minimal. This research indicated traffic tolerance among fine fescue species is positively associated with verdure biomass and cell wall content. It is also possible to select traffic tolerant cultivars within each species based on these traits with considerable phenotypic variability in wear tolerance. The development of NIRS calibration models will facilitate future breeding applications to rapidly identify fine fescue cultivars with greater cell wall content. The findings from this research will contribute to the sustainability of the turfgrass industry by improving screening techniques for developing traffic tolerant fine fescues cultivars for use on low-input landscapes.Ph.D.Includes bibliographical reference