Crop Science 41:909-913 (2001)
© 2001 Crop Science Society of America
NOTES
Distribution of buffalograss polyploid variation in the southern great plains
Paul G. Johnson*a,
Kevin E. Kenworthyb,
Dick L. Auldc and
Terrance P. Riordand
a Dep. of Plants, Soils, and Biometerology, 4820 Old Main Hill, Logan, UT 84322-4820
b Dep. of Agribusiness, Agronomy, Horticulture, and Range Management, Tarleton State Univ., Box T-0050, Stephenville, TX 76402
c Dep. of Crop and Soil Science, Texas Tech Univ., Plant Science, Room 263, Lubbock, Texas 79409-2122
d Dep. of Horticulture, 377 Plant Sciences, Univ. of Nebraska, Lincoln, NE 68583-0724
* Corresponding author (pjohnson{at}mendel.usu.edu)
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ABSTRACT
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Buffalograss [Buchloë dactyloides (Nutt.) Engelm.] is indigenous to the short-grass prairies of North America and is a polyploid series of diploid, tetraploid, and hexaploid individuals. It has a base chromosome number of x = 10. The distribution pattern of these ploidy levels is not well-defined, especially in the southern Great Plains. We predicted the ploidy levels of 273 buffalograsses from the southern Great Plains of North America using flow cytometry to measure cellular DNA content. The buffalograss accessions were grouped into four distinct ploidy level groups. Very few diploid accessions were collected (2.6% of the collection), and all were found in northwest Texas and eastern New Mexico. Tetraploid accessions (23% of the collection) were found exclusively in the western regions of the southern Great Plains. Hexaploids were the most prevalent ploidy level, representing 73% of the collection and found throughout the collection area. Pentaploid accessions were also found in field sites (1.8% of the collection). No clear pattern of adaptation for ploidy levels is apparent from these data. In other collections, cold hardiness appears associated with higher ploidy levels, but this pattern is not apparent in the southern Great Plains.
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INTRODUCTION
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BUFFALOGRASS is a warm-season perennial grass that has been the subject of substantial plant breeding and development work in recent years for use in forage and low-maintenance turfgrass areas. Buffalograss is a low-growing, sod-forming species with tolerance to drought, diseases, and wide temperature extremes (Savage, 1934; Wenger, 1943). The most recent breeding work has been for low-water use landscapes where buffalograss maintains better turfgrass quality than many cool-season grasses (Riordan et al., 1993).
Buffalograss is native to the North American Great Plains and is distributed north to south from Canada to Mexico and west to east from the eastern slope of the Rocky Mountains to the Mississippi Valley (Fig. 1). It is the dominant species in the short-grass prairie—the driest part of the Great Plains (Fig. 1).
Like many other prairie grasses, buffalograss comprises a polyploid series. The base chromosome number is x = 10 with diploid, tetraploid, and hexaploid plants reported. Morphologically, all three ploidy levels are indistinguishable. No characteristics have been found to consistently identify between them. All three ploidy levels have been documented in Mexico (Reeder, 1971) but diploids have been reported only in central Mexico and southeastern Texas (Huff et al., 1993). Hexaploids can be found throughout the Great Plains (Huff et al., 1993; Johnson et al., 1998). Buffalograss plants collected from Kansas, Nebraska, and Colorado are primarily hexaploids and tetraploids (Johnson et al., 1998). Tetraploids are also thought to be prevalent in the western-most regions (Huff et al., 1993). However, the actual distribution of the ploidy levels is not well-defined.
In this research, we studied a collection of buffalograsses collected from the southern Great Plains for distribution of ploidy levels, and report correlations with potential adaptational traits.
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Materials and Methods
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During 1994 and 1995, a systematic collection of 273 buffalograss plants was made during seven trips in the southern Great Plains. Each trip began and ended in Lubbock, TX. Grasses were collected from 242 sites that averaged 55 km apart, ranging from 1.6 to 160 km apart. At each collection site, a plant was selected based on color, but was representative of the population at that location. Plant color was involved in the collection process in order to build a breeding population for turfgrass variety improvement work. If two or more distinct populations were present at the collection site, each population was sampled and given separate collection numbers. When plants were collected, they were put in a plastic bag and transported to Lubbock, TX, and transplanted into a greenhouse. The collection area ranged from 27°35'N lat to 39°10'N lat and from 97°25'W long to 105°38'W long, encompassing an area >480000 km2 (Kenworthy et al., 1999).
Chromosome number was inferred by measuring nuclear DNA content using flow cytometry. The methods are described in Johnson et al. (1998). Previous work on DNA contents in buffalograss has shown a tight relationship between chromosome number and DNA content (Johnson et al., 1998). The elevation of each collection site was determined from three-and-a-half arc second resolution digital models. Climate data were 10-yr averages (1985–1995) for the closest National Weather Service Cooperative reporting station to the plant-collection locations. Statistical procedures (PROC GLM, PROC CORR) were performed on SAS 7.0 for Windows (SAS Inst., Cary, NC).
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Results and Discussion
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DNA content for the buffalograss accessions were grouped into four distinct ploidy levels, based on relationships of DNA content and inferred chromosome number (Table 1). The selection based partially on plant color, as described in the methods, did not appear to influence ploidy level of the collected plants. At 40 of the collection sites, two or more plants were selected, and only four of these sites had plants with differential ploidy levels.
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Table 1. Mean DNA contents for buffalograss accessions collected from the southern Great Plains and evaluated for ploidy level using flow cytometry.
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Diploid buffalograsses appear to be rare in natural environments. Only 2.6% of the collected plants were diploid, and all were collected in northwest Texas and eastern New Mexico (Fig. 2A). Diploid buffalograss had been identified in southeast Texas and Mexico, but these also were localized populations (Reeder, 1971; Huff et al., 1993). Although several diploid cultivars of buffalograss have exhibited good turfgrass performance, they appear to be rare in natural environments. Lack of cold hardiness in diploids has limited their adaptation to southerly locations (Johnson et al., 1998); for example, no diploids have survived a Nebraska winter (P. Johnson, unpublished data, 1998). The diploids described in this article originate from colder areas than diploids previously reported in the literature. These diploid accessions may be useful to investigate cold tolerance among diploid germplasm.
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Fig. 2. Distribution patterns of the diploid (A), tetraploid (B), pentaploid (C), and hexaploid (D) buffalograss individuals from a collection in the southern Great Plains.
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Tetraploid accessions were collected exclusively in the western regions of the collection area (Fig. 2B). Significant correlations were present when ploidy level and winter precipitation (r = 0.29; P < 0.001), autumn minimum temperature (r = 0.16; P < 0.01), and total precipitation (r = 0.37; P < 0.0001) of the collection locations were compared. Tetraploids in this collection were limited to the western parts of the collection area (Fig. 2B), supported by a significant correlation between ploidy level and longitude (r = 0.38; P < 0.0001). The western collection sites tend to have lower precipitation, especially in the spring (Fig. 3). However, the relationship with precipitation may be confounded with elevation.
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Fig. 3. Relationship between buffalograss ploidy level of individual collections and associated average annual precipitation and spring precipitation at each site location.
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Hexaploids represented 73% of the collection (Table 1) and were more common in the eastern parts of the collection area (Fig. 2D). Hexaploids are the dominant ploidy level in northern areas of the Great Plains, possibly relating to increased cold tolerance (Johnson et al., 1998). In the southern Great Plains, no relationship between latitude and ploidy level was observed (r = -0.08; P = 0.35). Because hexaploids were found throughout the collection area and throughout the Great Plains, the hexaploids appear to be the most broadly adapted.
Kenworthy et al. (1999) reported a relationship between fall dormancy characteristics and latitude in this same collection. Their data suggested the relationship was related to photoperiod adaptation. Ploidy level groups show significant differences in fall-dormancy ratings (Table 2); however, the effect of ploidy on fall dormancy may be confounded by other genetic differences.
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Table 2. Fall dormancy mean and range for buffalograss accessions collected from the southern Great Plains as separated into ploidy level by flow cytometry.
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The lack of clear patterns in ploidy-level distribution is not unusual. Keeler (1990) reported a general trend of higher ploidy levels in big bluestem (Andropogon gerardii Vitman) collected from western areas where the climate is drier and more variable. Interestingly, lower ploidy level in buffalograss (tetraploid) is more common in the drier, western regions (Fig. 2B).
This is the first report of pentaploid buffalograss occurring naturally in field sites (Fig. 2C). A pentaploid created by controlled crosses has been patented and commercialized as a vegetative turfgrass variety because of its dwarf growth habit and high turfgrass quality (Riordan et al., 1995). Triploid buffalograss plants, with DNA contents of 
1.4 pg DNA/nucleus, have been created by controlled crosses at Texas Tech University, but none have been located in natural collections. The rare occurrences of pentaploid plants (1.8%) suggest they are not competitive in natural or rangeland situations. Infertility and reduced competitiveness of unbalanced genomes was reported in big bluestem. Sexual reproduction of 9x and 7x plants was characterized by meiotic disturbance (Norrmann et al., 1997). The same meiotic behavior may occur in pentaploid buffalograss as well, limiting seed production and plant vigor.
Four explanations for polyploid polymorphism are summarized by Keeler (1990): (i) evolutionary or adaptive—increased ploidy levels confer adaptation to a new and different environment; (ii) transitional—one ploidy level gradually replaces another over the entire range; (iii) separate species—each ploidy level should be considered a distinct species; (iv) neutral—chromosome number has no adaptation or evolutionary significance.
Adaptive effects may be argued for greater cold tolerance in hexaploid buffalograss, which has allowed the species to spread into the northern Great Plains (Johnson et al., 1998). However, such a trend is not evident in the southern Great Plains where significant variation in winter temperature minimums also exist. In the region of our collection, ploidy level effects may be neutral. Potential adaptations of tetraploids to the western parts of the collection area need to be investigated further. This distribution pattern, together with diploids being isolated in a few areas, and hexaploids throughout the entire range, may point to the transitional scenario with hexaploids becoming dominant throughout the Great Plains. Variation in ploidy levels of buffalograss are not due to separate species, since the ploidy levels in buffalograss are nearly identical morphologically, are able to cross quite freely, and create fertile offspring.
In all three scenarios of polyploid polymorphism in buffalograss, many questions still remain and many environmental factors and plant characteristics have not been studied. Additional systematic collections and studies of competitiveness and physiological characteristics may provide insight.
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ACKNOWLEDGMENTS
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The authors thank Chad Kitchen and Benjamin Call for their assistance in preparing the climate data, and K. Arumuganathan for assistance with the flow cytometry methods. The authors also thank anonymous reviewers for their important suggestions for this manuscript.
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NOTES
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This research was supported in part by the Utah Agric. Exp. Stn., Utah State Univ., Logan, UT 84322-4810. Approved as journal Paper no. 7282.
Received for publication May 10, 2000.
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REFERENCES
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- Huff, D.R., R. Peakall, and P.E. Smouse. 1993. RAPD variation within and among natural populations of outcrossing buffalograss [Buchloë dactyloides (Nutt.) Engelm.]. Theor. Appl. Genet. 86: 927–934.[ISI]
- Johnson, P.G., T.P. Riordan, and K. Arumuganathan. 1998. Ploidy level determinations in buffalograss clones and populations. Crop Sci. 38:478–482.[Abstract/Free Full Text]
- Keeler, K.H. 1990. Distribution of polyploid variation in big bluestem (Andropogon gerardii, Poaceae) across the tallgrass prairie region. Genome 33:85–99.
- Kenworthy, K.E., D.L. Auld, D.B. Wester, R.E. Durham, and C.B. McKenney. 1999. Evaluation of buffalograss germplasm for induction of fall dormancy and spring green-up. J. Turfgrass Manag. 3:23–42.
- Norrmann, G.A., C.L. Quarin, and K.H. Keeler. 1997. Evolutionary implications of meiotic chromosome behavior, reproductive biology, and hybridization in 6X and 9X cytotypes of Andropogon gerardii (Poaceae). Am. J. Bot. 84:201–207.[Abstract]
- Reeder, J.R. 1971. Notes on Mexican grasses: IX. Miscellaneous chromosome numbers. Brittonia 23:105–117.
- Riordan, T.P., S.A. deShazer, J.M. Johnson-Cicalese, and R.C. Shearman. 1993. An overview of breeding and development of buffalograss. Int. Turfgrass Soc. Res. J 7:816–822.
- Riordan, T.P., J.M. Johnson-Cicalese, F.P. Baxendale, M.C. Engleke, R.E. Gaussoin, G.L. Horst, and R.C. Shearman. 1995. Registration of ‘315’ buffalograss. Crop Sci. 35:1206.[Free Full Text]
- Savage, D.A. 1934. Methods of re-establishing buffalograss in the Great Plains. p. 1–20. In USDA Circular 328. U.S. Gov. Print. Office, Washington, DC.
- Wenger, L.E. 1943. Buffalograss. Kansas Ag. Exp. Sta. Bull. 321. Kansas State Univ., Manhattan, KS.
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ABSTRACT
INTRODUCTION
