Proc. 56th Southern Pasture and Forage Crop Improvement Conference, Springdale, AR April 21-22, 2001
Eastern Gamagrass – Past, Present and Future Prospectus
USDA, ARS, SPRRS
Woodward, OK 73801
Eastern gamagrass, Tripsacum dactyloides (L.) L., has been an important segment of agriculture from the days the bison, Bison, bison, roamed the great plains, during the search for the origin of corn, Zea mays ssp mays, and corn improvement, and into the age of biotechnology and molecular biology. It is a native warm-season perennial bunchgrass, which is useful for grazing, stored forage, and soil amelioration and conservation. A distant relative of corn,, eastern gamagrass and other grasses in the tribe Andropogoneae have diverged beyond the norm of the grass family in specialized inflorescence structure. This is indicative of age or duration and/or rate of evolutionary change
Eastern gamagrass occurs from New York to Nebraska (40º latitude), southward through Kansas, Oklahoma and Texas, into northeastern Mexico, and eastward to the Atlantic and Gulf coasts. It is an extremely variable species with strains adapted to the prairies, coastal plains, semi-arid regions, deep sandy soils, rocky outcrops, riverbanks, and openings in forested areas. Thriving colonies can be observed on the Cimarron River flats and Canadian River bottoms in western Oklahoma and elsewhere known for soils with high salt content.
A BIT OF HISTORY – It is estimated that eastern gamagrass once covered one-third of the state of Texas and was fairly abundant throughout the southern Great Plains. The plains buffalo or bison, historically grazed through northern Mexico and Texas in their annual clockwise grazing circle through the central part of the United States (Polk and Adcock, 1964). The demise and near extinction of the American bison and eastern gamagrass occurred simultaneously in the mid to late nineteenth century as their territory was invaded and fenced by man for use by domestic animals. Over stocking, over grazing, and lack of a rest-use rotation practiced by the roaming bison, resulted in the near elimination of eastern gamagrass (Rechenthin, 1951).
Meanwhile, back east, land settlement preceded that of its western neighbors and most of the
botanists and philanthropists resided east of the Mississippi River. Hence, this grass of the western prairies was named eastern gamagrass. During the 1820-1840 several excerpts appeared in various eastern gazettes concerning the merits and use of eastern gamagrass and a few will be summarized below.
Dr. John Hardeman (Aug. 1826), reported collecting a grass 150 miles from his home in Franklin, MO, that was later identified as gamagrass. The grass so excited the good doctor that he transplanted it in his garden and when the crown reached 2 feet in diameter it was cut and weighed. The cutting weighed 52 lbs. green, and later 20 lbs. when dry. On the fourteenth day after cutting, regrowth of the plant was 18 inches, which led the good doctor to believe he would get another cutting. At this point he calculated the possible product of acre to be (43,560 ft. per acre, divided by 4 (2’ x 2’) = 10,890 plants per acre x 52 lbs. = 566,280 lbs green grass per acre and 10,890 x 20 = 217,800 lbs. dry hay per acre). He then theorized that if the second cutting was a much as the first, the possible product per acre would be 415,000 lbs. dry hay per year, allowing that a 2 foot circle was only 11/14 of a 2 foot square. Though mathematically possible, John could not believe it probable, so he divided this in half, and reduced the second cutting to yield one half of the first cutting and concluded “the cultivator of this grass to a high degree of probability, if not absolute certainty (will) get 100,000 lbs. of hay for each acre he shall plant with this grass.” John must have been a medical doctor who did his own billing.
James Magoffin (1831) obtained seed from Dr. John Hardeman of Missouri and evaluated the grass in Alabama. He stated, “A most accurate cutting and weighing, has determined, that an acre will yield (of pine land manured) from two hundred to two hundred and fifty thousand pounds of green grass during the summer, or from seventy-five to ninety tons of hay, and of the most nutritious kinds grown upon the earth.”
T.S.P. (1835) of Beaver Dam, VA cites his experiences north of the James River concerning the culture of gamagrass from the richest soil to that of only tolerable fertility. He “discovered but little difference in the luxuriance of its growth under these different circumstances – a result which may be attributed to the number and strength of the roots, which penetrate deeply into the stratum, and draw nourishment from sources not readily accessible to less vigorous plants.” After cutting he “observed its growth attentively for some time, and found that the blades grew an inch and a half per day so in the course of another month the grass had nearly attained its full size again.”
In his manual “The Grasses of Tennessee”, J.B. Killebrew (1878) described gamagrass as “one of the most beautiful grasses we have,” which occurs “abundantly throughout the Mississippi Valley on moist, slushy places.” This grass may be cut three or four times a year, and though in its native state it grows in swamps and thrives almost equally well on dry sandy ridges.”
Numerous early reports refer to the uncertainty of propagation by seed and recommend setting out slips of roots, i.e. vegetative propagation (T.S.P. 1835; Killebrew, 1878, 1898; Wilcox and Smith, 1905; Flint 1982). The tedious amount of hand labor and time associated with digging, dividing rootstalk, and hand transplanting gamagrass led an anonymous writer (1843) in the Southern Cultivator to conclude, “Not withstanding its long continuance – not withstanding it is nutritive to and relished by stock of all kinds, such is the aversion of the great body of agriculturists to incurring any extra labor, that we fear it never will be successfully introduced.”
THE TWENTIETH CENTURY – During the early nineteen hundreds, interest switched from gamagrass for forage to gamagrass for the improvement of corn. (Collins 1930; Weatherwax 1930; Longley 1941; Randolph 1952). Manglsdorf and Reeves (1931 and 1939) were the first investigators to obtain hybrids between corn and gamagrass. Farquharson (1957) reported a hybrid obtained by using a triploid gamagrass as the female parent x corn from Puna, Peru. Phenotypic alterations from interactions of corn and gamagrass genes were recorded by Maguire (1961) and Reeves and Bockholt (1964). The basic genome of corn can have gene exchange with at least one genome of polyploid gamagrass (Maguire 1962; Galinat 1971); however, permanent incorporation of large amounts of gamagrass genetic material is usually prevented by gametophylic barriers (deWet, et al. 1972).
The transfer of disease resistance from gamagrass to corn has been reported by Simone and Hooker (1976) and Berquist (1977). Genetically dominant resistance to anthracnose, fusarium stalk rot, northern and southern corn leaf blight, rust, and Stewart’s bacterial blight have been recovered in corn following hybridization with gamagrass (deWet 1979). Resistance to rootworm damage and water logged soils have resulted from gamagrass introgression into corn, as well as gametophytic apomixis, weak perennialism, increased tillering, and increased ears per node (deWet 1979).
By the nineteen seventies interest was renewed in eastern gamagrass for forage production. Problems with stand establishment and stand persistence were primary factors limiting potential of the grass (Ahring and Frank 1968). Problems were minimized by the use of moist pre-chill seed treatment or by winter dormant plantings to break seed dormancy. Stand maintenance was improved through rotation grazing, proper stocking rates, and the use of stubble barriers to control grazing height.
During this period, Oklahoma State University and certain other universities assigned graduate students to specific aspects of gamagrass research. Germplasm collections and assemblies were made by the USDA, NRCS Plant Materials Center and the USDA-ARS Southern Plains Range Research Station (SPRRS) at Woodward, OK. These germplasm nurseries proved invaluable for breeding, morphological, cytological, and molecular studies on the genetic diversity of eastern gamagrass. One example is a discovery of a mutant form of eastern gamagrass, T. dactyloides forma prolificum, Dayton et Dewald (Dewald and Dayton, 1985a), found in 1981 growing at the NRCS Plant Materials Center near Manhattan, KS. The origin of the seed source was traced back to a collection from Ottawa County, KS, where an additional gynomonoecious mutant form was found growing in a wild population. The variant sex form differs from the classical monecious form by having both pistillate and perfect rather than staminate spikelets in the terminal (tassel) portion of the inflorescence and by having two functional pistillate florets in the basal spikelets instead of one. A recessive major gene at a single locus regulates the change of the inflorescence from monoecious to gynomonoecious (Dewald et al., 1987). The inflorescence in highly feminized with a mean ratio of 0.5 (range 0.24 to 0.82) anthers per female flower (Dewald and Jackson, 1986). Potential seed set is increased 20 to 25-fold compared to the classical monoecious sex form, greatly increasing the number of hybrids, which could be obtained in a breeding program.
Eastern gamagrass has a range of chromosome numbers of diploid (2n = 2x =36), triploid (2n = 3x = 54), tetraploid (2n = 4x = 72), pentaploid (2n = 5x = 90), and hexaploid (2n = 6x = 108), (Farquharson, 1954; deWet et al., 1982). Diploids are exclusively sexual, whereas, polyploids reproduce as facultative apomicts (Brown and Emery, 1958; Burson et al., 1990; Sherman et al., 1991; Leblanc et al., 1995).
The wide range of chromosome numbers and different modes of reproduction complicate improvement through breeding. However, eastern gamagrass has a great deal of reproductive versatility and can be manipulated advantageously. Sexual diploids can be crossed with apomictic tetraploids to yield fertile triploids (Dewald et al., 1992). Fertile triploids provide a robust vehicle for exchanging germplasm between sexual diploids and apomictic polyploids. Apomictic triploids crossed with sexual diploids often yield tetraploids through fertilization of unreduced eggs, i.e. ploidy building or genome accumulation (Dewald and Kindiger, 1994; Kindiger and Dewald, 1994, 1997). Thus, the genetic constitution of diploids can be transferred to polyploids to further widen the genetic base available for breeding. Also, the apomictic mode of reproduction can be used to stabilize recessive traits from diploids into true breeding polyploids (Dewald and Kindiger, 1994).
The USDA-NRCS, the USDA-ARS, and the state universities of Kansas and Oklahoma released the first variety, “Pete” eastern gamagrass, in 1988. “Iuka IV” eastern gamagrass was released through the Grass Variety Review Board in 1995. Both of these varieties are sexual diploids best suited to the central states. San Marcos 434493, a tetraploid collected from the wild near San Marcos, TX, was increase and released in the USDA-NRCS in 1999. This variety could be useful in southern areas where “Pete” and “Iuka IV” are less vigorous than many southern tetraploids.
Elite germplasm releases include gynomonoecious diploids GSF-I and GSF-II (Dewald and Dayton, 1985b), fertile triploids FT-I, FT-2, FT-3, and FT-4 (Dewald et al., 1992), and a fertile gynomonoecious triploid FGT-1 (Dewald and Kindiger, 1996).
During the past 20 years planting of eastern gamagrass has increased dramatically, primarily because of a more plentiful supply of seed and increased knowledge concerning gamagrass management.
WHAT’S AHEAD? – The use of gamagrass as a forage should continue to be a valuable component of the livestock industry. Better adapted varieties should be available and knowledge concerning management considerations will increase through time. Eastern gamagrass is not a miracle grass, as there is no such thing, but it can be a valuable tool for use in livestock production systems.
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