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CROP BREEDING, GENETICS & CYTOLOGY

Genetic Progress from 40 Years of Orchardgrass Breeding in North America Measured under Hay Management

^a Dep. of Agronomy, Univ of Wisconsin-Madison, Madison, WI 53706-1597 USA
^b Dep. of Agronomy, The Pennsylvania State Univ., University Park, PA 16802 USA
^c Agric. and Agri-Food Canada, Ottawa, Canada K1A 0C6
^d Dep. of Plant Pathology, The Pennsylvania State Univ., University Park, PA 16802 USA

mdcasler{at}facstaff.wisc.edu

	ABSTRACT

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion REFERENCES

 
There has been considerable activity in breeding orchardgrass (Dactylis glomerata L.) cultivars in North America during the latter half of the 20th century, but little effort devoted to quantification of breeding progress. The objectives of this study were to quantify changes in mean cultivar performance for that time compared with the progress achieved from one cycle of half-sib progeny selection within the USDA population of orchardgrass accessions. Forty-two cultivars (32 North American cultivars and 10 European cultivars) were tested at three locations (Arlington, WI and Rock Springs, PA, and Ottawa, Ontario, Canada) in 1995 through 1997. Cultivars were grouped into three experiments by maturity class: early, medium, and late. North American cultivars averaged 3, 9, and 12% higher in forage yield than European cultivars for early, medium, and late maturity groups, respectively. Between 1955 and 1997, forage yield and ground cover of early-maturity cultivars increased by 2.5 Mg ha^-1 decade^-1 and 4.0% decade^-1, respectively. Forage nutritional value of medium-maturity cultivars increased during that time, although this was probably not due to direct selection. Significant gains were made in forage yield and Drechslera spp. leafspot reaction of cultivars derived from two individual breeding programs, although the majority of orchardgrass cultivars lack improvements in forage traits.

Abbreviations: FFRC, Farmers' Forage Research Coop • IVFD, in vitro digestibility of NDF • NDF, neutral detergent fiber • SEC, standard error of calibration • SECV, standard error of validation

	INTRODUCTION

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion REFERENCES

 
ORCHARDGRASS (cocksfoot) is a widely grown perennial forage grass used for both hay, silage, and pasture in North America. It is grown in 45 of the 48 contiguous United States (van Santen and Sleper, 1996) and in all Canadian provinces (Lawrence et al., 1995) where it is adapted to a wide range of habitats, including humid climates and irrigated dryland climates. It was introduced into Virginia in about 1760 (Beddows, 1968), presumably from continental Europe. Interest in the American colonies led to seed shipments back to Great Britain, which provided the initial impetus for British trading of orchardgrass seed beginning in 1763 (Beddows, 1968).

Although orchardgrass was extensively tested in the early part of the 20th century, it did not gain wide acceptance in North America or Great Britain until the 1930s (Beddows, 1968; Smith et al., 1986). Breeding programs began almost simultaneously in Great Britain and Canada in the 1930s and slightly later in the USA (Beddows, 1968; Lawrence et al., 1995; van Santen and Sleper, 1996). This was about 30 to 40 yr after initiation of North American and European breeding programs in other forage grasses, such as timothy, Phleum pratense L., and smooth bromegrass, Bromus inermis Leyss. (Casler et al., 1996). Orchardgrass breeding programs on continental Europe most likely began before the British programs (Beddows, 1968; Davies, 1952). The sensitivity of some orchardgrass germplasm to early spring frosts (Smith, 1948) may have delayed interest in developing orchardgrass breeding programs in North America.

Initial breeding efforts followed one of three general approaches: ecotype selection in Great Britain (Stapledon, 1928), mass selection in Canada (Lawrence et al., 1995), or clonal breeding in the USA (Alderson and Sharp, 1994; Hanson, 1972a). Despite the different approaches in these three countries, the overall approach followed a central theme: using natural selection to help identify superior germplasm. The initial British approach largely relied on identification and multiplication of superior existing natural strains. The Canadian mass selection programs focused largely on harvesting seed from plants that had survived severe winters. Breeding programs in the USA largely relied on development of large collections of clones from old pastures and hayfields, screening these clones in uniform nurseries, and creating synthetic cultivars from a small group of selected clones. By the 1950s, sufficient germplasm and information exchange between British, continental European, Canadian, and U.S. scientists had occurred that orchardgrass breeding programs in most countries had begun to resemble each other (Alderson and Sharp, 1994; Hanson and Carnahan, 1956; Lawrence et al., 1995).

Since the 1950s, clonal breeding has been the dominant approach to orchardgrass cultivar development. Source nurseries typically consist of a wide array of germplasm from which superior clones are selected and polycrossed. Polycross progeny testing was used in the development of approximately one-half of the orchardgrass cultivars bred in Canada, New Zealand, and the USA (Casler et al., 1997a). Following the polycross progeny test, mild selection pressures (26–67%) are used to eliminate the clones with the lowest general combining ability, and the remaining clones are polycrossed to form a synthetic cultivar. For cultivars developed in this manner, the only direct selection for forage yield on sward plots is the mild selection pressure among polycross families (used only 50% of the time) and postsynthesis selection among synthetics. Postsynthesis selection is probably applicable only in large commercial breeding programs that routinely generate several candidate synthetic cultivars each year (Casler, 1998; Casler et al., 1996); no such program has ever existed for orchardgrass in North America.

Although there have been numerous reports of genetic variation for yield in orchardgrass (Christie and Krakar, 1980; Knight, 1971; Stratton et al., 1979), there are no reports of the progress achieved from direct selection for forage yield. Recurrent selection for agronomic traits and seed production combined across four environments led to a 7 to 8% increase in sward-plot forage yield for two of four orchardgrass populations (Casler et al., 1997a). The lack of progress in all four populations when selection was practiced at only a single location suggested that genotype x environment interactions may seriously confound selection progress if selection is conducted at a single location. This may explain the lack of response for forage yield selection on a spaced-plant basis in many other forage species (Casler et al., 1996).

Estimated increases in forage yield of orchardgrass due to breeding in France and Italy during the 1970s and 1980s averaged 1 to 2% decade^-1 (Veronesi, 1991). This is approximately one-half the progress observed in tall fescue (Festuca arundinacea Schreb.) and perennial ryegrass (Lolium perenne L.) during that time. At least 51 cultivars of orchardgrass have been bred and released in Canada and the USA between 1955 and 1997 (Table 1 ; Alderson and Sharp, 1994; Bowley et al., 1994; Hanson, 1972b; Jung and Baker, 1985; Lawrence et al., 1995; van Santen and Sleper, 1996). Despite such a high level of breeding activity (1.2 new cultivars year^-1), there is no information on the progress that has been achieved from these breeding programs.

	Materials and methods

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion REFERENCES

 
Forty-two orchardgrass cultivars were included in these field experiments (Table 1). All cultivars were classified into early, medium, or late maturity classes on the basis of (i) prior information from forage tests in Wisconsin between 1981 and 1993 or, when this information was not available, (ii) information from the owner or breeder. The latter criterion was used only when necessary because this information typically is derived from maturity ratings in seed production environments or managements and may not reflect relative maturity in forage environments or forage management systems (Barker et al., 1997; Casler et al., 1997b).

Cultivars were chosen solely on availability of seed. The study included 32 of the 41 cultivars released in North America between 1955 and 1997 for which seed is still commercially available (Table 1). Sorted by decade, the study included all four cultivars from 1955 to 1959, four of six from 1960 to 1969, six of nine from 1970 to 1979, all nine from 1980 to 1989, and nine of 13 from 1990 to 1997. A chi-square test for independence indicated that the probability that any cultivar was included in the study was independent of its decade of release. Thus, the sample of cultivars was random with respect to year of release. A random sample of 10 European cultivars were included as representatives of improved, but potentially nonadapted, germplasm.

Each group of cultivars was planted in April or August 1994 at three locations: Arlington, WI; Rock Springs, PA; and Ottawa, ON. Soil types are Plano silt loam (fine-silty, mixed, mesic, Typic Argiudoll) at Arlington, Hagerstown silt loam (fine, mixed, mesic, Typic Hapludalf) at Rock Springs, and Manotick sandy loam (gray, Humo-Ferric Podzol) at Ottawa.

The experimental design for each group of cultivars at each location was a modified augmented design (Lin and Poushinsky, 1985). This involved creating a base Latin square design for each experiment (6 x 6 for the medium group or 5 x 5 for the early and late groups). Each unit of the Latin square was a whole plot of three subplots bordering each other on their long sides (Fig. 1) . Each subplot was planted to an individual cultivar. For each group, either five or six cultivars were arbitrarily designated as check cultivars (Table 1). Check cultivars were planted to the center subplot of each whole plot in the Latin squares. The remaining subplots were planted to other cultivars or experimental populations (data not shown). The number of replicates of each cultivar varied considerably, based only on availability of pure live seed (Table 1). Balance in the number of replicates per cultivar was sacrificed to obtain an identical experimental design and number of replicates among locations for ease of statistical analysis across locations. The modified augmented design was chosen because of the extreme imbalance in the number of replicates per cultivar and its potential for control of spatial variation.

View larger version (35K): [in this window] [in a new window]   Fig. 1 Diagram of a modified augmented design with whole plots in a five by five Latin square and three subplots per whole plot. Heavy lines are whole-plot borders and thin lines are subplot borders. Subplots measured 0.9 by 3.0 m. Stippled plots are the check plots, which were planted with five arbitrary cultivars in a Latin square arrangement

Each plot was harvested with a flail-type harvester beginning in 1995. Plots at Arlington and Ottawa were harvested for 3 yr, while those at Rock Springs were harvested for 2 yr. Three harvests per year were taken at Arlington and Rock Springs (early June, late July, and late September to late October) and two harvests per year were taken at Ottawa (late June and September). The entire plot was harvested at Arlington and Rock Springs and a 1.0-m swath was harvested from the center of each plot at Ottawa. A 300- to 500-g sample was taken from each plot at each harvest for dry matter determination. Forage yield for each plot was expressed as the sum across all harvests within each year. Nitrogen fertilizer was applied as follows: 80 kg N ha^-1 in early spring and after the first and second harvests at Arlington, 84 kg N ha^-1 in the spring and 56 kg N ha^-1 after each of the first two harvests at Rock Springs, and 80 kg N ha^-1 in the spring and 40 kg N ha^-1 after the first harvest at Ottawa. Applications of P and K were made according to results from soil tests.

Maturity was scored on each plot at Arlington in 1995 to 1997 and Ottawa in 1995 and 1996 using the 1 to 8 rating scale of Casler (1988): 1 = vegetative, 2 = boot, 3 = initial emergence, 4 = full emergence, 5 = elongated peduncle, 6 = initial anthesis, 7 = full anthesis, and 8 = postanthesis. Leafspot reaction (caused by natural inoculum of Drechslera spp., most likely D. dactylidis Shoem.) was visually rated immediately prior to second and third harvests at Arlington in 1995 to 1997 and Rock Springs in 1995 and 1996 using a scale of 0 to 5, where 0 = no symptoms to 5 = leaves completely diseased. Ground cover percentage of living crown tissue was visually rated on each plot immediately after the first cut of the last harvest year at each location. Six cultivars with low establishment were excluded from all analyses and from Table 1. All cultivars had 100% establishment ratings, allowing ground cover percentages to be considered a measure of persistence.

All forage samples were ground to pass a 1-mm screen in a Wiley-type mill and reground to pass a 1-mm screen in a cyclone mill. Samples were scanned with a near-infrared reflectance spectrophotometer and separate calibration subsets were chosen for each location (14–15% of the samples at each location) using modified partial least squares regression (Shenk and Westerhaus, 1991). Neutral detergent fiber (NDF) concentration was determined on all calibration samples using the procedure of Van Soest et al. (1991) with the omission of sodium sulfite and -amylase. In vitro digestibility of the NDF fraction (IVFD) was determined on all calibration samples in triplicate using the procedure of Casler (1987). Calibration and validation statistics for NDF were: standard error of calibration , standard error of validation , and . Calibration and validation statistics for IVFD were: SEC = 25.7 to 34.9 g kg^-1, r² = 0.71 to 0.76, SECV = 27.0 to 36.4 g kg^-1, and r²_val = 0.69 to 0.73. Moldy samples from some Wisconsin harvests prevented the development of satisfactory calibrations, so IVFD was not predicted for Wisconsin.

All data were analyzed by analysis of variance according to the modified augmented design model (Table 2) . All effects were assumed to be random. The Latin square portion of the analysis (Rows, Columns, and Latin Square Residual in Table 2) was computed from the 25 or 36 center plots of each whole plot (Fig. 1), while sums of squares for cultivars and the subplot residual were computed from an analysis of adjusted subplot values (Lin and Poushinsky, 1983). Subplot values were adjusted using Lin and Poushinsky's Method 1:

(1)

where X_ijk is the observation of the kth subplot in the ith row and the jth column, R_i is the mean of check plots in the ith row, C_j is the mean of check plots in the jth column, and M... is the overall mean of check plots. Thus, each subplot within a whole plot was adjusted according to the row and column means corresponding with its center plot. Adjusted plot values were also used in a combined analysis of variance across years and locations. All effects were assumed to be random. The relative efficiency of the design was computed for the Latin square subset of plots, using separate computations for row and column blocks (Steel et al., 1996).

	Results and discussion

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion REFERENCES

 
Experimental Design
Row blocks in the Latin square portion of the modified augmented design showed a range in relative efficiency for forage yield of 97 to 166% among locations and maturity groups, with a mean of 122%. Column blocks in the Latin square portion of the modified augmented design showed a range in relative efficiency for forage yield of 94 to 146%, with a mean of 116%. There were no patterns among either locations or maturity groups for relative efficiencies of row vs. column blocking. Thus, blocking in both directions was nearly equally effective for all trials. A simple randomized complete block design would have been less effective at all three locations.

Differences among cultivars were significant (P < 0.01) for nearly all variables of all trials with very few exceptions. The modified augmented design proved an adequate means of error control for cultivars with various degrees of replication. There were some significant (P < 0.05) cultivar x year and cultivar x location interactions. However, these were generally small enough that they did not lead to enormously different conclusions for different years of a trial or for different locations. While individual cultivars showed some changes in rank among locations and/or years, contrast effects and regressions were seldom affected by locations or years because of the buffering effect of using several cultivars per group. Therefore, all results are presented as means across all years and locations.

North American vs. European Germplasm
North American cultivars were significantly higher in forage yield than European cultivars for all three maturity groups (P < 0.05; Table 3) . The superiority of North American cultivars was 2% for the early group, 9% for the medium group, and 12% for the late group. North American and European cultivars did not differ in ground cover, indicating that the lack of adaptation of European cultivars to these North American environments was due to reduced vigor, not reduced persistence. The largest differences in forage yield, in the medium and late maturity groups, appeared to be associated with differences in NDF concentration and IVFD. For these two groups, North American cultivars averaged 1.8% higher in NDF and 2.3% lower in IVFD than European cultivars. It is possible that these differences may have arisen directly from the differences in forage yield. Selection for reduced NDF or increased IVFD was not an integral component of European breeding programs during the time that these cultivars were developed (Van Wijk et al., 1993).

Orchardgrass was first introduced from Europe to North America in approximately 1760 (Beddows, 1968; Christie and McElroy, 1995). Apart from `Hercules' and `Avon', which are no longer available, the first North American cultivars were developed in 1955 (Alderson and Sharp, 1994; Lawrence et al., 1995). These first cultivars largely represented the product of 200 yr of natural selection for adaptation to North America. The most accurate estimate of genetic changes during this time is impossible to obtain because the original introductions and the 1950s germplasm pools have all been lost. Furthermore, extremely old hayfields or pastures planted to original introductions, if they still exist, no longer represent either the original introductions or their 1950s genetic state because of the ongoing effects of natural selection. The comparison of North American vs. European cultivars includes both the effects of 200 yr of natural selection and 40 yr of breeding in North America. These effects indicated large genetic changes in adaptation in the medium and late groups and small changes in the early group, as a result of the combined effects of natural selection and breeding in North America.

North American Cultivars: 1955 to 1997
Overall changes in forage yield and ground cover between 1955 and 1997 were significant only in the early maturity group (P < 0.05; Table 4) . The 0.15 Mg ha^-1 decade^-1 (2.5% decade^-1) increase in forage yield for the early group is slightly larger than estimates from France and Italy during the 1970s and 1980s (Veronesi, 1991). Part of this increase in forage yield could be attributed to increased persistence, as measured by ground cover (3.6 percentage units decade^-1 or 4.2% decade^-1). There was also a small decrease in Drechslera leafspot reaction of -4.8 and -5.5% decade^-1 for the medium and late groups, respectively (P < 0.05). The concentration of NDF decreased by 0.4% decade^-1 and IVFD increased by 0.6% decade^-1 in the medium-maturity group (P < 0.05). This result is surprising, given that none of the cultivars in this test were specifically selected for improved nutritional value.

In the early maturity group, Hallmark was developed by selection partly within `Potomac' as an alternative to Potomac. Hallmark had 3.0% higher forage yield (6.59 vs. 6.40 Mg ha^-1; P < 0.05) and 1.3% higher ground cover (94 vs. 92%; P < 0.05) than Potomac. Benchmark was developed by the FFRC breeding program in Indiana to replace Hallmark. We were unable to show any improvement in forage yield, ground cover, or Drechslera leafspot reaction of Benchmark compared with Hallmark (Table 5) , although we recognize that FFRC most likely based their release on more numerous and different test sites than ours. Furthermore, Benchmark may also represent an improvement in some traits important in seed production environments, something that we did not measure. Benchmark was 0.6% lower in NDF and 0.8% higher in IVFD than Hallmark, indicating a previously unknown improvement in nutritional value (Winsett et al., 1991). The improved nutritional value of Benchmark was probably due to unknown genetic correlations between forage nutritional value and its selection criteria, that is, unconscious selection (Casler et al., 1996).

Also in the late group, AC Nordic and AC Splendor represented significant improvements over Rideau, from which they were selected (Table 5). These two cultivars averaged 8.6% higher forage yield and 20% higher ground cover, despite a 0.6- to 0.8-unit shift toward later maturity than Rideau at the time of harvest. AC Splendor also showed a significant 18.2% reduction in Drechslera leafspot reaction. Both AC Nordic and AC Splendor showed significant improvements in IVFD, averaging 1.2 and 3.4% higher than Rideau, respectively. As with Benchmark, these improvements were probably due to unconscious selection.

Finally, Shawnee, which was derived largely from Pennlate and other Pennsylvania germplasm in the late group, showed a 7.3% reduction in forage yield and a 14.6% reduction in ground cover compared with Pennlate (Table 5). Shawnee germplasm was selected in Pennsylvania up to the early 1980s, which might explain its significant 36.4% reduction in Drechslera leafspot reaction. Beginning in the early 1980s, Shawnee was selected exclusively in Oregon seed production environments for disease resistances. Although Shawnee may represent an improvement over Pennlate in Oregon disease resistances and seed production, its relatively low ground cover and forage yield suggest a severe relaxation of selection pressure for these traits in forage environments of the eastern USA. Shawnee had 2.1% lower NDF and 2.7% higher IVFD than Pennlate, but this was probably due, in part, to its later mean maturity at these three locations (partial emergence for Shawnee vs. partial peduncle elongation for Pennlate).

The significant gains and losses in forage traits for these three breeding programs clearly demonstrate that regression estimates of genetic progress were diluted by cultivars that did not represent improvements in forage traits. The majority of orchardgrass cultivars in the marketplace do not represent improvement in forage yield, persistence, forage nutritional value, or Drechslera leafspot reaction in forage production environments. As pointed out for Benchmark and Shawnee, many recent cultivars may indeed represent improved seed production or traits important in seed production environments. This emphasizes the dichotomy that exists among orchardgrass breeders who generally focus only on traits that can be measured in their local environment (Barker et al., 1997; Casler et al., 1997b). Concomitant improvements in both forage and seed traits are possible through multilocation efforts (Barker et al., 1997; Casler et al., 1997a). Currently, the FFRC program is the only orchardgrass breeding program in the USA that is using a proven multilocation selection model.

	ACKNOWLEDGMENTS

 
We thank Dick Todd (Penn. State Univ.), Andy Beal (Wisconsin), and Klaus Jakubinek (Ottawa) for their assistance with field plot establishment, maintenance, and data collection. We thank Amy Chemerys (deceased) and Brian Macafee (Penn. State Univ.) for their assistance in laboratory data collection.

Received for publication June 14, 1999.

	REFERENCES

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion REFERENCES

 

• Alderson, J., and W.C. Sharp. 1994. Grass varieties in the United States. Agric. Handb. 170 (Revised). U.S. Gov. Print. Office, Washington, DC.
• Barker R.E., Casler M.D., Carlson I.T., Berg C.C., Sleper D.A., Young W.C., III. Convergent–divergent selection for seed production and forage traits in orchardgrass. II. Seed yield response in Oregon. Crop Sci. 1997;37:1054-1059.[Abstract/Free Full Text]
• Beddows A.R. A history of the introduction of timothy and cocksfoot into alternate husbandry in Britain. 1. The year 1763 and its significance. J. Br. Grassl. Soc. 1968;23:317-321.
• Bowley S.R., Hancock D., Wood D. Jay orchardgrass. Can. J. Plant Sci. 1994;74:339-340.
• Carmer S.G., Seif R.D. Calculation of orthogonal coefficients when treatments are unequally replicated and/or unequally spaced. Agron. J. 1963;55:387-389.[Abstract/Free Full Text]
• Casler M.D. In vitro digestibility of dry matter and cell wall constituents of smooth bromegrass forage. Crop Sci. 1987;27:931-934.[Abstract/Free Full Text]
• Casler M.D. Performance of orchardgrass, smooth bromegrass, and ryegrass in binary mixtures with alfalfa. Agron. J. 1988;80:509-514.[Abstract/Free Full Text]
• Casler M.D. Genetic variation within eight populations of perennial forage grasses. Plant Breed. 1998;117:243-249.
• Casler M.D., Berg C.C., Carlson I.T., Sleper D.A. Convergent–divergent selection for seed production and forage traits in orchardgrass. III. Correlated responses for forage traits. Crop Sci. 1997;37:1059-1065 a.[Abstract/Free Full Text]
• Casler M.D., Carlson I.T., Berg C.C., Sleper D.A., Barker R.E. Convergent–divergent selection for seed production and forage traits in orchardgrass. I. Direct selection responses. Crop Sci. 1997;37:1047-1053 b.[Abstract/Free Full Text]
• Casler M.D., Pedersen J.F., Eizenga G.C., Stratton S.D. Germplasm and cultivar development. In: Moser L.E., et al. , ed. Cool-season forage grasses. Madison, WI: ASA, CSSA, SSSA, 1996:413-469 Agron. Monogr. 34..
• Christie B.R., Krakar P.J. Performance of advanced generation hybrids of orchardgrass (Dactylis glomerata L.). Can. J. Plant Sci. 1980;60:479-483.
• Christie B.R., McElroy A.R. Orchardgrass. In: Barnes R.F., et al. , ed. Forages. Vol. I: An introduction to grassland agriculture, 5th ed Ames: Iowa State Univ. Press, 1995:325-334.
• Davies W. The grass crop, its development, use and maintenance. London: E. and F.N. Spon, 1952.
• Duvick D.N. Genetic contributions to advances in yield of U.S. maize. Maydica 1992;37:69-79.
• Everson L.E., Hotchkiss D.K. A comparison of the blowing and hand methods for the purity analysis of Dactylis glomerata seed. Seed Sci. Technol. 1977;5:451-462.
• Hanson A.A. Breeding of grasses. In: Youngner V.B., McKell C.M., eds. The biology and utilization of grasses. New York: Academic Press, 1972:36-52 a.
• Hanson A.A. Grass varieties in the United States. Washington, DC: U.S. Gov. Print. Office, 1972 b Agric. Handb. 170..
• Hanson A.A., Carnahan H.L. Breeding perennial forage grasses. Washington, DC: U.S. Gov. Print. Office, 1956 USDA Tech. Bull. 1145..
• Jung G.A., Baker B.S. Orchardgrass. In: Heath M.E., et al. , ed. Forages: The science of grassland agriculture, 4th ed Ames: Iowa State Univ. Press, 1985:224-232.
• Knight R. A multiple regression analysis of hybrid vigour in single crosses of Dactylis glomerata L. Theor. Appl. Genet. 1971;41:306-311.
• Lawrence T., Knowles R.P., Childers W.R., Clark K.W., Smoliak S., Clarke M.F. Forage grasses. In: Slinkard A.E., Knott D.R., eds. Harvest of gold: The history of field crop breeding in Canada. Saskatoon: Univ. Ext. Press, 1995:275-315 Univ. of Saskatchewan,.
• Lin C.S., Poushinsky G. A modified augmented design for an early stage of plant selection involving a large number of test lines without replication. Biometrics 1983;39:553-561.
• Lin C.S., Poushinsky G. A modified augmented design (type 2) for rectangular plots. Can. J. Plant Sci. 1985;65:743-749.
• Shenk J.S., Westerhaus M.O. Population definition, sample selection, and calibration procedures for near infrared reflectance spectroscopy. Crop Sci. 1991;31:469-474.[Abstract/Free Full Text]
• Smith D., Bula R.J., Walgenbach R.P. Forage management, 5th ed Dubuque, IA: Kendall/Hunt Publ. Co, 1986.
• Smith D.C. The breeder's ways and means. In: Stefferud A., ed. Grass, The yearbook of agriculture, 1948. Washington, DC: U.S. Gov. Print. Office, 1948:331-341.
• Stapledon R.G. Cocksfoot grass (Dactylis glomerata L.): Ecotypes in relation to the biotic factor. J. Ecol. 1928;16:71-104.
• Steel R.G.D., Torrie J.H., Dickey D.A. Principles and procedures of statistics: A biometrical approach, 3rd ed New York: McGraw-Hill, 1996.
• Stratton S.D., Sleper D.A., Matches A.G. Genetic variation and interrelationships of in vitro dry matter disappearance and fiber content in orchardgrass herbage. Crop Sci. 1979;19:329-333.[Abstract/Free Full Text]
• van Santen E., Sleper D.A. Orchardgrass. In: Moser L.E., et al. , ed. Cool-season forage grasses. Madison, WI: ASA, CSSA, SSSA, 1996:503-534 Agron. Monogr. 34..
• Van Soest P.J., Robertson J.B., Lewis B.A. Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccarides in relation to animal nutrition. J. Dairy Sci. 1991;74:3583-3597.[Abstract]
• Van Wijk, A.J.P., J.G. Boonman, and W. Rumball. 1993. Achievements and perspectives in the breeding of forage grasses and legumes. p. 379–383. In M.J. Baker, et al. (ed.) Proc. XVIII Intl. Grassl. Congr. Palmerston North, NZ. 8–21 Feb. 1993. NZ Grassl. Assoc., Palmerston North, New Zealand.
• Veronesi F. Achievements in fodder crop breeding in mediterranean Europe. In: den Nijs A.P.M., Elgersma A., eds. Fodder crops breeding: Achievements, novel strategies, and biotechnology. Wafeningen, the Netherlands: Pudoc, 1991:25-30.
• Winsett B.L., Stratton S.D., Baluch S.J. Registration of `Benchmark' orchardgrass. Crop Sci. 1991;31:492.[Free Full Text]
• Woodfield D.R., Caradus J.R. Genetic improvement in white clover representing six decades of plant breeding. Crop Sci. 1994;34:1205-1213.[Abstract/Free Full Text]

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