Published in Crop Sci. 44:884-890 (2004).
© 2004 Crop Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
TURFGRASS SCIENCE
Genetic Differentiation of Tetraploid Creeping Bentgrass and Hexaploid Redtop Bentgrass Genotypes by AFLP and their Use in Turfgrass Breeding
Georgina V. Vergara and
Suleiman S. Bughrara*
Dep. of Crop and Soil Sci., Michigan State Univ., Room 286 Plant and Soil Sci. Building, East Lansing, MI 48824
* Corresponding author (bughrara{at}msu.edu).
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ABSTRACT
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The turf industry in the last decade has seen doubling in number of new creeping bentgrass [Agrostis stolonifera var. palustris (Huds.) Farw. and A. stolonifera var. stolonifera Huds.] cultivars, many with unknown variability and lineage. Understanding the genetic diversity of putative parental and wild stocks would be useful in plant breeding programs. Amplified fragment length polymorphism (AFLP) analysis was conducted to investigate genetic variability among old and new cultivars of creeping bentgrasses, redtop bentgrasses (Agrostis gigantea Roth), plant introductions, and selected creeping bentgrass genotypes with resistance to gray snow mold (Typhula incarnata Lasch). Seven chosen primer combinations resulting in 355 polymorphic markers were used to differentiate the bentgrasses. Three groups were extracted by principal component analysis (PCA). With unweighted pair group method with the arithmetic mean (UPGMA) analysis, mean similarity coefficients of creeping bentgrass genotypes found in the first group was 0.78. Creeping bentgrasses in the USA were clustered as a subgroup and separated from European plant introductions, indicating that most selection and genetic exchanges in the last fifty years have evolved locally. Redtop bentgrasses were the most diverse and were found in different groups. Selected lines from northern Michigan, MI 20104, MI 20215, and MI 203164, were well differentiated from the other cultivars and would be advantageous to use as sources of disease-resistant traits and for development of populations for future gene mapping.
Abbreviations: AFLP, amplified fragment length polymorphism • MSU, Michigan State University • PCA, principal component analysis • sc, similarity coefficient • TE, tris-ethylenediamine tetraacetic acid • UPGMA, unweighted pair group method with the arithmetic mean
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INTRODUCTION
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CREEPING BENTGRASSES (2n = 4x = 28) are the premier and most widely used cool-season turfgrasses for golf course putting greens, tees and fairways in the USA (Funk, 1998). Redtop bentgrasses (2n = 6x = 42) are widely used in seed mixtures for rapid vegetation cover. These two species of bentgrasses are distinguished from other species by their profuse creeping stolons forming dense mats, vigorous shallow roots, and their attractive range of bluish-green to grayish appearance. From 1927 to 1994, <20 cultivars have been released by different institutions and private seed companies in the USA, but within the past 8 yr, the number of cultivars that have been bred has doubled. Creeping bentgrasses are synthetic products created from the crossing of three or more clones and recurrent selection. Improved turf quality and appearance, tolerance to close mowing, regenerative and seed yield potential, and tolerance to diseases are some important parameters for selection. Some of these new cultivars may be closely related but their interrelationships are unknown. Diversity within creeping bentgrasses appears limited as their genetic variability may be narrow (0.007 to 0.08%) as revealed by isozyme polymorphism (Yamamoto and Duich, 1994; Warnke et al., 1997). Plant introductions from germplasm collections could be used to widen the genetic base.
Morphologically, creeping bentgrasses are difficult to distinguish and taxonomic confusion has resulted in many synonymous names for the tetraploid species. Agrostis stolonifera L. was listed as being synonymous with A. alba var. palustris Huds., A. alba var. stolonifera (L.) Sm., A. stolonifera var. compacta Hart., A. stolonifera var. palustris (Huds.) Farw., and A. maritima Lam. (Bioinformatics Working Group, 1998; Plant Gene Resources of Canada, 2003). Hexaploid bentgrasses were referred to as A. stolonifera sp. gigantea Huds., A. gigantea L., or A. alba sp. gigantea Huds. Adding to the taxonomic complexity are other factors, such as the outcrossing nature of bentgrasses, ability to form interspecific hybrids, and environmental fluctuations that may result in differences in phenotypic expressions and inconsistencies in classification. A more stable tool like DNA molecular marker technology may help resolve identification and offer insights to the degree of genetic variability and relationships among cultivars and to help define future breeding strategies.
Molecular marker studies with AFLP analyses have been used to differentiate bermudagrass (Cynodon spp.) genotypes (Zhang et al., 1999) and to construct a genomic map of zoysiagrass (Zoysia spp.) (Ebina et al., 1999). Some bentgrass cultivars and species have been differentiated by random amplified polymorphic DNA (RAPD) (Golembiewski et al., 1997, Scheef et al., 2001) and restriction fragment length polymorphism (RFLP) (Caceres et al., 2000). Our recent work in the study of genetic diversity in the Agrostis species with AFLPs has shown the advantage of this technique for biodiversity studies, distinguishing fourteen species of bentgrasses into seven major groups (Vergara and Bughrara, 2003). Stoloniferous bentgrasses from several countries formed a single cluster comprised of A. stolonifera L. or A. palustris Huds., A. gigantea L., A. mongolica Roshev., and A. transcaspica Litv. The percentage of genetic dissimilarity (5 to 18%) within plant introductions of creeping bentgrasses indicated considerable potential for the improvement of turf.
Turfgrass breeders are currently interested in developing superior cultivars of A. stolonifera var. palustris with resistance to major diseases such as dollar spot (caused by Rutstroemia floccosum, teleomorph of Sclerotinia homeocarpa F.T. Bennett) (Powell, 1998), brown patch (Rhizoctonia solani Kühn), and snow molds [Typhula spp. and Microdochium nivale (Fr.) Samuels & I.C. Hallett] (Vargas, 1994; Hsiang et al., 1999). In 2000 and 2001, the Michigan State University (MSU) turf breeding program isolated and selected experimental lines MI 20104, MI 20215, and MI 203164 with resistance to gray snow mold from replicated controlled screening trials. Our objective was to use AFLPs to investigate genetic variability among old and new cultivars of creeping bentgrasses, redtop bentgrasses, and plant introductions, and to differentiate MSU experimental lines of creeping bentgrasses. Predictive estimates of genetic variation will be useful in planning turfgrass breeding programs and developing heterotic populations. Marker data and identified AFLP primer combinations will be useful in future mapping studies.
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MATERIALS AND METHODS
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Plant Materials and DNA Extraction
Bulk leaf samples from 25 plants each of creeping bentgrass cultivars Penncross, Providence, L-93, Penn G2, Penn A4, Emerald, and redtop bentgrass cultivar S. Redtop were used. Widely used cultivars developed during different periods of time were chosen. Leaf samples from identical selected clones of MI 20104, MI 20215, and MI 203164 selected from northern Michigan golf courses in 2000 were included for comparison. In addition, PIs of eight creeping bentgrass accessions and two redtop bentgrass accessions (source: USDA Plant Introduction Station, Pullman, WA) from different countries were included (Table 1). Fresh leaf tissues were ground in liquid nitrogen and an equal volume of extraction buffer was added. The extraction buffer consisted of Tris-EDTA-HCl, SDS, and NaCl with 0.38 g of sodium bisulfite per 100 mL of the buffer. The mixture was incubated at 65°C for 20 min, followed by the addition of 10 mL of 5 M potassium acetate. After 20 min of incubation in ice in a gyratory shaker, the suspension was centrifuged at 3000 g RCF (Sorvall RT7 model) for 20 min at 5°C. The supernatant was collected, to which 2/3 volume of cold isopropanol was added to precipitate the DNA. All DNA samples were treated with RNase dissolved in TE (tris-ethylenediamine tetraacetic acid) buffer and twice reprecipitated with 1/10 volume of 3 M sodium acetate followed by two volumes of chilled absolute ethanol. Extracted DNA was stored in 1% TE buffer. DNA quality was checked by running 5 µL of the undigested samples in 1% agarose gel containing TBE buffer and compared with EcoRI digested samples. DNA quantification was done with a DyNA Quant 200 Fluorometer (Pharmacia Biotech, CA).
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Table 1. Cultivars, Michigan State University experimental lines (MIs), and plant introductions (PIs) of creeping and redtop bentgrasses (Agrostis spp.) examined, year released or collected, and their sources.
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Amplified Fragment Length Polymorphism Analysis
Approximately 150 to 200 ng of DNA was used for AFLP analysis of each genotype. Digestion was conducted by two restriction enzymes, EcoRI, a 6-bp cutter and Mse-I, a 4-bp cutter. The AFLP procedure used in this study was as described by Vos et al. (1995) with modifications. Preamplification was done on a PTC-100 thermal cycler (MJ Research, Inc., Waltham, MA) at 72°C for 2 min, 30 cycles of 94°C for 30 sec, 60°C for 30 sec, 72°C for 1 min, followed by elongation at 72°C for 5 min and 4°C hold. The PCR products from initial ligation of adapters were checked on 1.5% TBE agarose gel. Combinations of fluorescent (*) dye labeled E and M primers each with three selective nucleotides at the 3' ends were used. The following E* primers were used: E*-ACA and E*-AGC. The following M primers were tested: M-CAT, M-CAG, M-CGG, M-CGA, M-CTT, M-CCT. The 15-µL selective amplification mixture consisted of 15 pmol E*-primer, 75 pmol M-primer, 2 mM dNTP, 1 x PCR buffer, 37.5 mM MgCl2, and 1.0 unit Taq Polymerase in deionized distilled water. The PCR cycling sequence used for selective amplification was as recommended by Vos et al. (1995). Products from selective amplification were checked initially on 1.5% agarose and diluted four times with 0.1 TE buffer. For separation on acrylamide gels, samples consisted of 0.5 µL of the amplified product and 0.5 µL of loading dye. The samples were denatured at 95°C for 5 min before loading and run on a 6% Long Ranger polyacrylamide gel with 0.7 x TBE buffer by a LI-COR DNA Analyzer 4200 (Lincoln, NE) at a constant 800 V for 6 h at 50°C.
Data Analyses
Gels were visualized with the software Gene ImagIR 4.0 (Scanalytics, Inc., Fairfax, VA). Each informative polymorphic band was scored manually as 1 for presence and 0 for absence. Analyses were done with Numerical Taxonomy and the Multivariate Analysis System, NTSYS v.2.1 (Rohlf, 2000). Genetic similarities based on Jaccard's coefficients (Jaccard, 1908) were calculated among all possible pairs with the SIMQUAL option and ordered in a similarity matrix. The similarity matrix was run on Sequential, Agglomerative, Hierarchical, and Nested clustering, SAHN (Sneath and Sokal, 1973) with UPGMA as an option (Sokal and Michener, 1958). Cophenetic correlation was calculated to measure goodness of fit. The PCA was run with the CPCA option (NTSYS) to identify the number of groups based on eigenvectors and verified with SYSTAT. The three-dimensional PCA plot was generated from the NTSYS program with AFLP markers as observations and bentgrass genotypes as the operational taxonomic units. The TREE module of NTSYS v.2.1 was used to produce the dendrogram (Rohlf, 2000).
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RESULTS
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From the initial 12 primer combinations, seven combinations were chosen for clarity and repetitiveness in duplicated gel runs (Table 2). A total of 355 polymorphic markers were scored for the 20 genotypes from the seven combinations. The number of bands varied with each primer combination, ranging from 100 to 150 bands and the number of polymorphic markers ranged from 25 to 100 per individual lane. Primer combination E-ACA/M-CAT gave the most robust polymorphism. Pairwise similarity coefficients (sc) were computed on the basis of shared and unique amplification products with UPGMA (Table 3). The genetic similarity coefficients ranged from 0.55 to 0.93. The most similar bentgrass genotypes were the PIs from Switzerland and Sweden (sc = 0.93) and the most dissimilar would be Penncross and PI 443051 (sc = 0.56).
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Table 3. Genetic similarity coefficients for 20 genotypes of creeping and redtop bentgrasses based on amplified fragment length polymorphisms.
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With CPCA subroutine programs of NTSYS, a rotated PCA with the markers as observations was used to determine the number of groups based on Eigen values >1. Three groups were extracted which explained 58% of the total variance. The first component accounted for 44% of the total variance with the cultivar S. Redtop bearing the lowest component loading (Fig. 1)
. Seventeen genotypes were distinguished by the first component. The second component, which accounted for 8% of the variation, separated Groups 1 and 2. The third component accounted for 5% of the variation and distinguished PI 443051.
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Fig. 1. Three-dimensional plot of principal component analysis with 355 amplified fragment length polymorphism markers (observations) and 20 bentgrass genotypes defining three groups marked as 1, 2, and 3 from the CPCA and plot options of NTSYS v. 2.1 (Rohlf, 2000).
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From the UPGMA analyses, a dendrogram was generated (Fig. 2)
. The cophenetic correlation was calculated (r = 0.95) as a measure of goodness of fit of the similarity indices. The mean similarity coefficient for all creeping bentgrasses in the first group was 0.78. Similarity coefficient was lower between the redtop bentgrasses (sc = 0.64). Group 2 consisted of A. palustris (Iran and Russia) and Group 3 consisted only of PI 443051, A. gigantea (USA). The dendogram showed a similarity coefficient of 0.64 for the three groups.
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Fig. 2. The unweighted pair group method with the arithmetic mean dendrogram of creeping and redtop bentgrasses with data from 355 amplified fragment length polymorphism markers.
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The dendrogram incorporating data from 355 markers showed that 14 of the 17 genotypes in Group 1, namely Penncross, Providence, L-93, Penn-G2, Penn A4, Emerald, MI 20104, MI 20215, MI 203164, PI 251945 (Austria), PI 235440 (Switzerland), PI 235541 (Sweden), PI 269838 (Denmark), and PI 494119 (the Netherlands), were clustered close together at sc = 0.78. Cultivar Penncross may share genetic similarities with modern cultivars by a mean sc = 0.75. The 14 genotypes were slightly differentiated from PI 204390 and PI 383584 (Turkey) and S. Redtop. Cultivar S. Redtop was the most genetically distant in the first group. MI 20104 was most similar with Emerald (sc = 0.88), while MI 20215 and MI 203164 were more similar to Providence (sc = 0.79 and 0.83, respectively). Providence and L-93 had a high sc = 0.83 and shared close identity with MI 20215 and MI 203164. Dendrogram results showed the three genotypes of A. gigantea did not group together. PI 443051, A. gigantea (USA) separated from cultivar S. Redtop (USA) and from PI 383584 (Turkey).
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DISCUSSION
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Differentiating Old and New Cultivars of Creeping Bentgrasses
Most developed cultivars of creeping bentgrass (A. stolonifera var. palustris) in the USA such as Penncross, Penn A4, L-93, and others came from phenotypic recurrent selection of three or more clones descended from selection of adapted lines which were thought to be from earlier European origin. Warnke et al. (1997) used isozyme polymorphisms to distinguish between several creeping bentgrasses. Eighteen bentgrasses were divided into two groups on the basis of cluster analyses. The first group included 10 cultivars (Penncross, Emerald, Cobra, Crenshaw, Seaside, Penneagle, Putter, Trueline, Viper, and 18th Green). With the exception of Crenshaw, they were all strongly aligned with creeping cultivars. ‘Seaside’ is thought to be the oldest cultivar within the group and may have provided some of the germplasm used in the development of some bentgrasses in the grouping. Their genetic distance calculated from Nei's distance formula ranged from 0.007 to 0.08. The second group contained the cultivars Pennlinks, Southshore, ProCup, Lopez, Providence, SR1020, National, and Cato. Both groups were differentiated from PI 251945, which is of European origin by genetic distance of 0.27. They found genetic differences to be small within cultivars and suggested that the PI line could be a source to broaden genetic diversity of bentgrasses in the USA.
In this study, UPGMA similarity coefficients from AFLP showed Penncross (1955) shared genetic similarities by as much as 75% with modern creeping bentgrass cultivars and belonged to the same group. Cultivars Penncross and Emerald were in the same cluster by AFLP and supported similar findings by Warnke et al. (1997). Another similar observation to their findings from our results was that PI 251945 (Austria) has a range of sc = 0.65 to 0.77 to U.S. cultivars. PI 251945 and other PIs from Switzerland, Sweden, Denmark, and the Netherlands would be useful to expand genetic variability in creeping bentgrass. In contrast to the results of Warnke et al. (1997), AFLP analysis showed that the genetic differences among U.S. cultivars might be higher than the previous estimates with isozymes. Variability is important because selection becomes more effective when diversity is high.
In Fig. 2, more recent cultivars, Providence (1987) and L-93 (1995) clustered together with sc = 0.84. Providence was a consistently top-rated (best five) bentgrass in the annual National Turfgrass Evaluation Program (NTEP 98-8) Putting Green and Fairway Test (Morris, 1997, Table 4) and in trials throughout the world. The progenitors of Providence were five clones that Dr. Richard Skogley of the University of Rhode Island has selected as being unique and superior to Penncross since 1965 (Seed Research Reports of Oregon, 2003). The newer cultivars, Penn G2 and Penn A4 (1995) were clustered together at sc = 0.80 and differentiated from its early predecessor Penncross. Pennsylvania State University developed cultivars with the epithet Penn. Providence, Penn G2, and Penn A4 were reported as having better resistance to dollar spot in NTEP 02-3 trials (Morris, 2001a, Table 32) and would be useful as genetic stocks. Creeping bentgrass from Turkey (Central Asia) was the most genetically distant in the first group and would be highly useful and informative for future mapping studies. Redtop bentgrass cultivar S. Redtop in the Group 1 cluster was shown to share some genetic similarity with the tetraploid creeping bentgrasses. In contrast to creeping bentgrasses, redtop bentgrass is not used as fine turf but would be an important source of other important traits like drought and heavy metal tolerance (Winterhalder, 1990). Creeping bentgrasses (USA) clustered separately as a subgroup from the PIs from Europe at sc = 0.78, an indication that most development, selection, and genetic exchanges in the last 50 yr occurred locally. Support for European lineage for U.S. creeping bentgrasses was also shown by AFLP results in Group 1 in this study. Previous findings comparing genetic similarities of plant introductions of Agrostis species with AFLPs showed that bentgrasses from the USA were closer to European PIs than accessions coming from other parts of the world (Vergara and Bughrara, 2003).
Differentiating MSU Experimental Lines with Other Creeping Bentgrasses
The MSU experimental lines were collected from old (>50 yr) northern Michigan golf courses which have not been overseeded for the last 10 yr. Materials from these golf courses have been through natural selection pressures for abiotic and biotic stresses, making them excellent genetic stocks for turf breeding programs. Data from AFLPs showed that the selected experimental lines were differentiated from other creeping bentgrasses and showed the closest genetic similarity to Providence, L-93, and Emerald. The two cultivars L-93 and Emerald are currently internationally known for their dark, dense, and aggressive growth habit. L-93 was rated premier out of 25 cultivars in the National Bentgrass Test—1998 (Morris, 2001b, Table 6) on fairways and tees and also performed better in heat stress than Penncross (Xu and Huang, 2001). Cultivar Emerald is a descendant of a single synthetic clone originating from Sweden and is widely used in blends of two or more creeping bentgrasses in the USA. Emerald is important as it also has moderate tolerance to heat like Providence, as compared with most cool-season bentgrasses. The high similarity coefficients (0.80–0.88) to top-rated modern cultivars provided predictive estimates by which MI 20104, MI 20215, and MI 203164 with resistance to snow mold disease may be used to improve performance of newer cultivars without radically altering their genetic components. Correspondingly, cultivars to which the sc values were less gave indication of the high genetic diversity favorable for studies on combining abilities. Populations derived from crosses with large differences in polymorphic markers may be used to map the snow mold disease resistance trait.
Results from the UPGMA analysis showed that germplasm materials or plant introductions from Europe might also be used to widen the genetic base of modern U.S. creeping bentgrasses. The estimated mean genetic similarity among all creeping bentgrass genotypes was 0.78 and suggested considerable diversity from which selection for improved cultivars may be generated. Creeping bentgrass from other subgroups (Central Asia) which are more differentiated by AFLPs would correspondingly further increase genetic variability. Diverse parental combinations would create segregating populations of various heterotic groups from which superior clones may be selected.
Genetic Dissimilarity of Tetraploid and Hexaploid Creeping Bentgrasses
The AFLP analysis indicated that most tetraploid creeping bentgrasses were grouped together and separated from hexaploid stoloniferous bentgrasses (Fig. 2). PI 204390 (A. palustris, Turkey) was the most genetically distant among the tetraploid creeping bentgrasses in this study and may share closer genomic constitution with PI 383584 (A. gigantea, Turkey) than the other accessions. Having similar geographic origins, possible genetic introductions between the progenitors of the two species may have occurred and allowed them to evolve sympatrically. Interspecific hybridizations between tetraploid and hexaploid bentgrasses like A. stolonifera x A. gigantea were known to occur naturally and are easy to produce (Davies, 1953; Jones, 1955). The ability of cross-speciation enhances opportunities to transfer other important traits such as tolerance to heavy metals and poor soils, drought tolerance, and vigorous growth habit found in A. gigantea to creeping bentgrass.
Hexaploid bentgrasses (A. gigantea) have been found to be genetically diverse within species and differentiated from the tetraploid A. palustris by use of AFLPs (Table 3). The three A. gigantea accessions were found to group separately from each other. S. Redtop (USA) has only a sc = 0.59 with PI 443051 (A. gigantea) (USA). Our results suggest that their genomic constitutions (A1A1A2A2A3A3) may be dissimilar and may have descended from different diploid and tetraploid progenitors. Much of the extensive variation in A. gigantea could have been generated by multiple or repeated cycles of hybridization of multiple origins. Our findings in the AFLP analysis of a number of Agrostis species were similar and indicated that possibly only the A1A1 genome may be shared by the different accessions of A. gigantea (Vergara and Bughrara, 2003). Future cytogenetic and hybridization studies may be done to explain their differences.
Applications to Turfgrass Breeding
Turf breeders may gain advantage in selection when breeding materials are highly heterogenous and populations could be efficiently differentiated. Difficulty in differentiating outcrossing allopolyploid turfgrass species morphologically may be overcome with AFLP analyses. This study has shown considerable genetic dissimilarities between old and new cultivars, germplasm, and MSU experimental lines. Dendrogram analysis revealed that U.S. creeping bentgrass cultivars have locally evolved and differentiated from European germplasm. Genetic similarity coefficients may predict which cultivars are more similar or distant and help define strategies for breeding. The AFLP data suggested that A. stolonifera var. palustris cultivars in the USA are highly heterogenous but may be further diversified with materials from Europe and Turkey. Experimental materials from MSU with disease resistance to snow mold could be used to improve cultivars. Other important traits found in plant introductions of A. gigantea may be used to improve S. Redtop or transferred to creeping bentgrass cultivars by interspecific hybridization. In the future, the identified primer combinations and polymorphic marker data identified herein may be used to monitor introgression, map important traits, and for protection of indigenous materials and developed cultivars.
Received for publication February 21, 2003.
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REFERENCES
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|---|
- Bioinformatics Working Group. 1998. BONAP Poaceae listing [Online]. Available at http://www.csdl.tamu.edu/FLORA/bonapfams/bonzzpoa.htm (updated 20 Oct. 1998; accessed June 2003; verified 26 Jan. 2004). Texas A&M Bioinformatics Working Group, College Station, TX, and the Biota of North America Program, Chapel Hill, NC.
- Caceres, M.E., F. Pulpilli, E. Piano, and S. Arcioni. 2000. RFLP markers are an effective tool for the identification of creeping bentgrass (Agrostis stolonifera L.) cultivars. Genet. Res. Crop Evol. 47(4):455–459.
- Davies, W.E. 1953. The breeding affinities of some British species of Agrostis. Br. Agric. Bull. 5:313–316.
- Ebina, M., M. Kobayashi, S. Kasuga, H. Araya, and H. Nakagawa. 1999. An AFLP based genome map of Zoysia grass. p. 278. In Plant and Animal Genome VII abstracts, San Diego, CA. 17–21 Jan. 1999. PAG, San Diego, CA.
- Funk, R. 1998. Opportunities for genetic improvement of underutilized plants for turf. p. 23–26. In Proc. Annu. Rutgers Turfgrass Symp., 7th, Cook College, NJ. 13–16 Jan. 1998. Rutgers Univ., New Brunswick, NJ.
- Golembiewski, R.C., T.K. Danneberger, and P.M. Sweeney. 1997. Potential of RAPD markers for use in the identification of creeping bentgrass cultivars. Crop Sci. 37:212–214.[Abstract/Free Full Text]
- Hsiang, T., N. Matsumoto, and S. Millet. 1999. Biology and management of Typhula snow molds of turfgrass. Plant Dis. 83:788–798.
- Jaccard, P. 1908. Nouvelles recherches sur la distribution florale. Bull. Soc. Vaudoise Sci. Nat. 44:223–270.
- Jones, K. 1955. Species differentiation in Agrostis. III. A. gigantea Roth. and its hybrids with A. tenuis Sibth. and A. stolonifera L. J. Genet. 54:394–399.
- Morris, K. 1997. National Bentgrass (Fairway/Tee) Test—1993. Ratings of bentgrass cultivars grown on a fairway or tee. NTEP no. 98–8. National Turfgrass Evaluation Program, Beltsville, MD.
- Morris, K. 2001a. National Bentgrass (Putting Green) Test—1998. Dollar spot ratings of bentgrass cultivars. NTEP no. 02–3. National Turfgrass Evaluation Program, Beltsville, MD.
- Morris, K. 2001b. National Bentgrass (Putting Green) Test—1998. Mean turfgrass quality ratings of bentgrass cultivars. NTEP no. 02–3. National Turfgrass Evaluation Program, Beltsville, MD.
- Plant Gene Resources of Canada. 2003. PGRC—Search GRIN-CA [Online.] Available at: http://pgrc3.agr.ca/index_e.html [cited May 2003; modified 2 Dec. 2003; verified 26 Jan. 2004]. Agriculture & Agri-Food Canada, Saskatoon, SK, Canada.
- Powell, J.F. 1998. Seasonal variation and taxonomic clarification of the dollarspot pathogen: Sclerotinia homeocarpa. Ph.D. diss. Michigan State Univ., East Lansing, MI.
- Rohlf, F.J. 2000. NTSYS-pc numerical taxonomy and multivariate analysis system version 2.1 manual. Applied Biostatistics, New York.
- Scheef, E.A., M. Casler, and G. Jung. 2001. Development of SCAR markers for identification of bentgrass species. In Annual Meetings Abstracts [CD-ROM]. ASA, CSSA, and SSSA, Madison, WI.
- Seed Research Reports of Oregon. 2003. Seed research reports: Providence creeping bentgrass [Online]. Available at: http://www.sroseed.com/Products/PDF/Providence.pdf (cited June 2003; verified 26 Jan. 2004). Publ. 1019. Seed Research of Oregon, Corvallis, OR.
- Sneath, P.H.A., and R.R. Sokal. 1973. Numerical Taxonomy: The principles and practice of numerical classification. Freeman, San Francisco.
- Sokal, R., and C. Michener. 1958. A statistical method for evaluating statistical relationships. Univ. Kansas Sci. Bull. 38:1409–1438.
- Vargas, J.M., Jr. 1994. Management of turfgrass diseases. CRC Press, Boca Raton, FL.
- Vergara, G.V., and S. Bughrara. 2003. AFLP analyses of genetic diversity in bentgrass. Crop Sci. 43:2162–2171.[Abstract/Free Full Text]
- Vos, P., R. Hogers, M. Bleeker, M. Reijans, T.V.D. Lee, M. Hornes, A. Fritjers, J. Pot, J. Poleman, M. Kuiper, and M. Zabeau. 1995. AFLP: A new technique for DNA fingerprinting. Nucleic Acids Res. 23(21):4407–4414.
- Warnke, S.E., D.S. Douches, and B.E. Branham. 1997. Relationships among creeping bentgrass cultivars based on isozyme polymorphisms. Crop Sci. 37:203–207.
- Winterhalder, K. 1990. The trigger-factor approach to the initiation of natural regeneration of plant communities on industrially damaged lands at Sudbury, Ontario. p. 215–226. In H. Hughes et al. (ed.) Restoration '89, the New Management Challenge: Proc. 1st Annu. Meeting of the Soc. for Ecological Restoration, Oakland, CA. 16–20 Jan. 1989. The Univ. of Wisconsin Arboretum, Soc. for Ecological Restoration, Madison.
- Xu, Q., and B. Huang. 2001. Morphological and physiological characteristics associated with heat tolerance in creeping bentgrass. Crop Sci. 41:127–133.[Abstract/Free Full Text]
- Yamamoto, I., and J.M. Duich. 1994. Electrophoretic identification of cross-pollinated bentgrass species and cultivars. Crop Sci. 34:792–798.[Abstract/Free Full Text]
- Zhang, L.H., P. Ozias-Akins, G. Kochert, S. Kresovich, R. Dean, and W. Hanna. 1999. Differentiation of bermudagrass (Cynodon spp.) genotypes by AFLP analyses. Theor. Appl. Genet. 98:895–902.
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TOP
ABSTRACT
INTRODUCTION
