New England Regional Turfgrass Foundation Research

Wear Stress Mechanisms in Cultivars of Creeping and Velvet Bentgrass
Progress report for 2005 submitted to the NERTF
Principle Investigators
J. S. Ebdon and J. M. Dowgiewicz Department of Plant, Soil and Insect Sciences 12F Stockbridge Hall University of Massachusetts Amherst, MA 01003-0410 Phone: 413-545-2506 E-mail: sebdon@pssci.umass.edu
W. M. Dest Professor Emeritus University of Connecticut Storrs, CT 06268
EXECUTIVE SUMMARY

Wear and soil compaction are major stresses that limit the function and quality of turfgrass under intensely trafficked conditions. A number of bentgrass cultivars are commercially available for use on golf courses as putting surfaces, however, their tolerances and associated mechanisms to wear have not been studied extensively. Such studies may allow breeders to efficiently identify those grasses better adapted for use in golf, and to refine cultural recommendations to improve wear tolerance. The objectives of this research are (i) evaluate overall wear tolerance among cultivars of creeping and velvet bentgrass, and (ii) identify specific mechanisms (plant factors) associated with wear tolerance. Wear was assessed in the field on 27 bentgrass cultivars grown on a USGA sand based rootzone as part of the 2003 NTEP Bentgrass (Putting Green) test. Plots were mown daily at 1/8 inch, fertilized at % Ib N per growing month, and irrigated to prevent stress. Significant wear injury was applied on all entries using 50 passes with a walk behind mower fitted with a grooming brush adjusted to operate in the free-floating position. Wear treatments were applied on 27 October, 2005. Wear injury was assessed on 2, 4, and 5 November using a 1 to 9 rating scale (9=no injury, 6=minimum acceptable), and then averaged. Velvet bentgrass cultivars exhibited 50% greater tolerance to wear compared to creeping bentgrass entries. Velvet cultivars ranged in wear (tolerance) from 4.78 to 7.11 while creeping bentgrass cultivars ranged from 2.22 to 3.56. Six of the seven velvet bentgrass entries evaluated exhibited acceptable wear tolerance while none of the 20 creeping bentgrass cultivars provided acceptable wear tolerance. All velvet bentgrass cultivars were statistically equivalent to their non-wear checks 2 weeks after wear treatments were applied. None of the creeping bentgrass cultivars had fully recovered to their untreated wear portions. This diversity in wear tolerance between Agrostis species suggest that plant factor at the mechanistic level may explain this diversity observed in wear tolerance. Greenhouse and field measurements will be made to identify those plant characteristics (morphological and physiological) that accurately predict wear in the field.

INTRODUCTION

Creeping bentgrass (Agrostis st%nifera L.) and velvet bentgrass (Agrostis canina L.) are the predominant cool-season turfgrass of choice for use in putting greens in the northern tier states such as New England. Damage from wear is immediate and is the result of bruising and crushing injury to turfgrass shoots. Conversely, compaction is a chronic, soil related stress initially expressed at the root level in response to low soil oxygen and high soil strength. Wear and compaction from vehicular and foot traffic can cause direct injury to both turfgrass shoots and roots, reducing turfgrass quality and function (Bonos et aI., 2001). Additionally, traffic can cause secondary problems by increasing disease severity and weed encroachment from annual bluegrass (Poa annua L.). Studies have shown that bentgrass cultivars with the ability to resist annual bluegrass encroachment is related to its superior tolerance to traffic (Murphy et aI., 2001).

The need for wear tolerant turfgrass will increase in the future as the use and demand for golf turf continue to increase. A basic and fundamental understanding of wear stress develops from studies where only one stress is active. Accordingly, wear damage must be evaluated within a short period (7 days) following initial wear treatments to avoid being confounded by the plants response to soil compaction. Studies where repeated wear treatments are imposed over long periods (several months) may be evaluating the plants response to predominately compaction, or at a minimum some combination of the two (Carrow and Petrovic, 1992). Under these conditions of prolong traffic the aspects of true wear are difficult to separate from the confounding interactions between wear and compaction, except where compaction resistant rootzones (uniform sands) are used.

Wear tolerance between species has been shown to be correlated with several plant characteristics including total cell wall content (TCW), leaf width, leaf tensile strength, verdure, shoot density, and leaf moisture content (LMC) (Shearman and Beard, 1975a, b, c). These differences between species in morphological and physiological characteristics and wear may not necessarily have application within a particular species. Some early research to understand wear tolerance has been conducted at the intraspecies (cultivar) level (Beard, 1973) and more recently to address wear mechanisms within new ecotypes of seashore paspalum (Trenholm et aI., 2000) and Kentucky bluegrass (Brosnan et aI., 2005). However, data specific to wear mechanisms in bentgrass species and cultivars are limited. Unless those characteristics are identified, breeders will not be able to develop selection criteria important in identifying cultivars with improved wear tolerance. Furthermore, such studies are beneficial to developing or refining management strategies that may be used by turf practitioners to alter such characteristics.

There has been little agreement between studies to identify plant characteristics associated with improved wear tolerance because wear and compaction often occur in various combinations. Bourgoin et al. (1985) investigated the relationship between plant characteristics among cultivars of cool-season turfgrass and wear. They reported that within perennial ryegrass, cultivars with higher shoot density and greater LMC and TCW were generally associated with higher wear tolerance. However, their study was conducted over several months, suggesting that wear and compaction effects in combination were being evaluated along with recuperative potential, and not necessarily wear tolerance alone. Brosnan et al. (2005) evaluated wear tolerance and various plant characteristics in cultivars of Kentucky bluegrass in response to short-term exposures to simulated traffic (i. e., predominately wear). They found that wear tolerant Kentucky bluegrasses were also associated with greater TCW, but observed lower LMC with wear tolerant cultivars, which contradicts Bourgoin et al. (1985) earlier investigation with perennial ryegrass. These studies indicate to accurately screen for wear tolerance, plant factors must be determined using the species-cultivars of interest rather than extrapolating data from other species.

The objectives of this study are (i) to evaluate the overall wear tolerance among cultivars of creeping and velvet bentgrass and (ii) to identify specific plant factors (wear mechanisms).

MATERIALS AND METHODS

Wear treatments were be applied to 27 cultivars. The cultivars are part of the 2003 National Turfgrass Evaluation Program (NTEP) trial. Plots were established in October 2003 at the Joseph Troll Turf Research Center, South Deerfield, MA, University of Massachusetts Amherst. The test entries include 7 velvet and 20 creeping bentgrass cultivars. Plots were arranged as a randomized complete block design with 3 replicates and were maintained under well-irrigated conditions to prevent stress, mowed 7 times per week at 1/8 inch, fertilized at % Ib N per growing month, and preventative fungicides were applied.

Ebdon, Dowgiewicz and Dest

NERTF 2005 Report: Wear Tolerance in Bentgrasses

Wear treatments were applied as a strip within replicates (split block) using 50 passes with a Toro Flex mower fitted with a grooming brush adjusted to operate in the free-floating position. Approximately 1/3 of the total plot area was exposed to wear. Wear was applied as a single wear event on 27 October, 2005. The mid-fall period was selected to minimize the potential for regrowth and recovery during the application and assessment of wear. Wear injury was assessed using a visual rating scale (1 to 9, 9=no injury, 6=minimum acceptable). Visual wear tolerance ratings were made on three different dates, 2, 4, and 5 November, 2005, and were then averaged. Initial wear injury at the day of treatment (ODA T) appears as bruising and crushing injury (blackish discoloration) followed by the loss in chlorophyll (chlorosis) and necrosis by day 5 after wear treatment (5DAT). Recovery from wear injury was evaluated approximately 2 weeks after treatment (2WAT) on 13 November, 2005. Wear treatments will continue into the 2006growing season. Monthly turfgrass quality (visual rating, 1 to 9 scale, with 9=highest quality), were taken from both wear treated and untreated check plots.

The statistical top and bottom five cultivars (10 cultivars in all) will then be selected for further study. This selection will allow for comparisons to be made in wear between cultivars exhibiting diverse wear tolerance (i. e., tolerant vs. intolerant) in relationship to shoot and physiological characteristics. Measurements will be taken on unmown-space plants maintained in the greenhouse according to the methods described by Ebdon et al. (1998) and Brosnan et al. (2005) using sand-filled, flexible slant tubes (Lehman and Engleke, 1985). Plant breeders typically evaluate plant characteristics from space planted nurseries (Bourgoin and Mansat, 1977), therefore space plants have some relevance to evaluations used by turfgrass breeders.

Experimental material to be used for greenhouse study will be established using pure (authentic) seed obtained from NTEP. After establishment, the following measurements will be made in both the greenhouse and field.

Wear Related Plant Measurements: Greenhouse and Field Studies

1. Leaf turgidity, measured using the following expression: [(fresh weight-dry weight)/(turgid weight-dry-weight)]100. Measured on the 1st or 2nd fully expanded leaf blade.
2. Leaf growth rate, as described by Ebdon et al. (1998) and Brosnan et al. (2005).
3. Leaf number per shoot (tiller), as described by Ebdon et al. (1998).
4. Rhizome number, total number of secondary lateral shoots per plant, as described by Ebdon et al. (1998) and Brosnan et al. (2005).
5. Moisture percentage, measured as: [100-(dry weight/fresh weight)] for both leaf blade and shoot (tiller).
6. Leaf tensile strength, measure as the tension (grams) required to reach the breaking point and to tear a leaf blade in half. Measured on the 1st or 2nd fully expanded leaf blade according to the methods described by Trenholm et al. (2000).
7. Leaf and stem flexibility as described by Sun and Liddle (1993).
8. Leaf width, measured at mid point on the 1 st or 2nd fully expanded leaf blade, as described by Ebdon et al. (1998) and Brosnan et al. (2005).
9. Tiller density, total number of primary lateral shoots per plant, as described by Ebdon et al. (1998) and Brosnan et al. (2005).
10. Verdure, total shoot biomass (dry weight) per plant at harvest.
11. Plant moisture content, measured according to expression (ii) on a whole plant basis, derived from verdure. (xii)
12. Rooting density by depth, 0 to 4,4 to 8,8 to 12, 12 to 16, 16 to 20, and 20 to 24 inches according to the methods of Lehman and Engleke (1985).
13. Leaf and stem cell wall components (total cell wall, lignin, lignocellulose, hemicellulose, cellulose), as described by Goering and Van Soest (1970) and Brosnan et al. (2005).

The greenhouse study will be conducted in the Winter of 2006 and repeated in 2007. Greenhouse measurements (i-xiii) will also be taken on the same 10 cultivars from untreated field plots (no wear) during the spring of 2006 and 2007. Analysis will be conducted to determine which field and greenhouse plant characteristics best predict wear tolerance in the field. At the end of the each field season (2006 and 2007), bulk density measurements will be taken from wear treated and untreated control plots to determine the extent of soil compaction,

RESULTS

Significant differences were observed in wear tolerance between creeping and velvet bentgrass cultivars (Table 1). In general, there was little difference in overall turfgrass quality between creeping and velvet bentgrass entries in the non-wear portions of test plots at the time wear treatments were applied on 27 October, 2005. Turf quality ratings recorded on 29 October ranged from 5.67 (Penncross, Pennlinks II) to 7.00 (9200, Declaration, SRX 1GD) for creeping bentgrass cultivars while velvet entries ranged from 6.33 (SR-7200) to 7.00 (Greenwich, Legendary). Almost all of the Agrostis species (25 out of 27 entries) provided acceptable turf quality under non-wear treated conditions (Fig. 1). Overall, the range in turfgrass quality for untreated wear plots that was observed across all entries of creeping and velvet bentgrass (5.67 to 7.00) was approximately 20%.

Wear injury in test plots was significant and this caused considerable separation between species and cultivars due to the effects of wear. For example, visual wear ratings ranged from 2.22 (Pennlinks II creeping bentgrass) to 7.11 (Greenwich velvet bentgrass) (Table 1). This range in wear tolerance is approximately 70% and 3.5 times the diversity observed in non-wear treated plots. These results indicate that significant genetic variation in wear tolerance exist and suggest the potential to select and develop genotypes (cultivars) of Agrostis for wear tolerance. Brosnan et al. (2005) observed a 50% variation in Kentucky bluegrass wear tolerance using similar methods and rating scale (1 to 9) in evaluating wear. They also reported significant relationships between plant factors and wear tolerant and intolerant cultivars of Kentucky bluegrass.

Velvet bentgrass cultivars exhibited significantly superior wear tolerance than creeping bentgrass entries. Velvet entries ranged from 4.78 (SR-7200) to 7.11 (Greenwich) while creeping bentgrass cultivars ranged from 2.22 (Pennlinks II) to 3.56 (235050) (Table 1). None of the 20 creeping bentgrass cultivars that were tested provided acceptable wear tolerance (> 6, 1 to 9 rating scale). Conversely, 6 of the 7 velvet bentgrass entries provided minimum acceptable wear tolerance (Fig. 2). In our studies, the worn portions of all velvet bentgrass entries reached cover ratings 2WA T equal to their unworn check portions (Table 1, Fig. 3). None of the creeping bentgrass cultivars had fully recovered from the wear stress 2WAT. So, selecting wear tolerant grasses will permit play to be rescheduled sooner on trafficked surfaces.

These studies indicate that velvet bentgrass is wear tolerant in comparison to wear intolerant creeping bentgrass. Previous studies reported for Kentucky bluegrass (Brosnan et aI., 2005) suggest the genetic diversity in wear tolerance observed here with Agrostis species may be due to plant factors at the mechanistic level.

REFERENCES

Beard, J. B. 1973. Turfgrass science and culture. Prentice-Hall. Englewood Cliffs, NJ.

Bonos, S. A, A E. Watkins, J. A Honig, M. Sosa, T. Molar, J. A Murphy, and W. A Meyer. 2001. Breeding cool-season turfgrass grasses for wear tolerance using a wear simulator. p. 137-145. In K. Carey (ed.) Proc. 9th Int. Turfgrass Res. Conf., Toronto, ON Canada. 15-21 July. Int. Turfgrass Soc., and Royal Canadian Golf Assoc., Oakville, ON.

Bourgoin, B., and P. Mansat. 1977. Comparisons of micro-trials and space planted nurseries with dense swords as means for evaluating turfgrass genotypes. p. 3-9. In J. B. Beard (ed.) Proc. 3rd Int. Turfgrass Res. Conf., Munich, Germany. 11-13 July. Int. Turfgrass Soc., ASA, CSSA, SSSA, Madison, WI.

Bourgoin, B., P. Mansat, B. Ait Taleb, and M. H. Quaggog. 1985. Explicative characteristics of treading tolerance in Festuca rubra, Lolium perenne, and Poa pratensis. p. 235-242. In F. Lemaire (ed.) Proc. 5th Int. Turfgrass Res. Conf., Avigon, France. 1-5 July. Inst. Nat. de la Recherche Agron., Paris.

Brosnan, J. T., J. S. Ebdon, and W. M. Dest. 2005. Characteristics of diverse wear tolerant genotypes of Kentucky bluegrass. Crop Sci. 45:1917-1926. Carrow, R N., and A M. Petrovic. 1992. Effects of traffic on turfgrass. p. 285-330. In Turfgrass (eds.) D. V. Waddington, RN. Carrow, and R C. Shearman. Agronomy Monogr. 32. ASA, CSSA, and SSSA, Madison, WI.

Ebdon, J. S., and A M. Petrovic. 1998. Morphological and growth charactersitics of low- and high-water use Kentucky bluegrass cultivars. Crop Sci. 38:143-152. Goering, H. K., and P. J. Van Soest. 1970. Forage fiber analysis (apparatus, reagents, procedures, and some applications). USDA Agric. Handb. 379. U. S. Gov. Print. Office, Washington, DC.

Lehman, V. G., and M. C. Engleke. 1985. A rapid screening techni~ue for genetic variability in turfgrass root systems. p. 770-776. In F. Lemaire (ed.) Proc. 5th Int. Turfgrass Res. Conf., Avigon, France. 1-5 July. Inst. Nat. de la Recherche Agron., Paris.

Murphy, J. A, H. Samaranayake, J. A Honig, arid T. J. Lawson. 2001. Annual bluegrass invasion in bentgrasses under traffic. In Agronomy abstracts. ASA, Madison, WI.

Shearman, R C., and J. B. Beard. 1975a. Turfgrass wear mechanisms: I. Wear tolerance of seven turfgrass species and quantitative methods for determining wear injury. Agron. J. 67:208-211.

Shearman, R C., and J. B. Beard. 1975b. Turfgrass wear mechanisms: II. Effects of cell constituents on turfgrass wear tolerance. Agron. J. 67:211-215.

Shearman, R C., and J. B. Beard. 1975c. Turfgrass wear mechanisms: III. Physiological, morphological, and anatomical characteristics associated with turfgrass wear tolerance. Agron. J. 67:208-211.

Sun, D., and M. J. Liddle. 1993. Trampling resistance, stem flexibility, and leaf strength in nine Australian grasses and herbs. Bioi. Conserv. 65:35-41.

Trenholm, L. E., R N. Carrow, and R R Duncan. 2000. Mechanisms of wear tolerance in seashore paspalum and bermudagrass. Crop Sci. 40:1350-1357.