Proc. 56th Southern Pasture and Forage Crop Improvement Conference, Springdale, AR April 21-22, 2001
Bahiagrass and other Paspalum species:
An overview of the plant breeding efforts in the Southern Coastal Plain
A.R. Blount1 ablount@gnv.ifas.ufl.edu,
K.H. Quesenberry2 clover@gnv.ifas.ufl.edu,
P. Mislevy5,
R.N. Gates 4 and T.R.Sinclair5
1. Univ. of Florida, NFREC, Marianna, FL
2. Univ. of Florida, Agronomy Dept., Gainesville, FL
3. Univ. of Florida, Range Cattle Research and Education Center, Ona, FL
4. USDA-ARS, Crop Genetics and Breeding Research Unit, Coastal Plain Experiment
Station, Tifton, GA
5. USDA-ARS, Crop Genetics and Environmental Research Unit, Gainesville, FL
Bahiagrass (Paspalum notatum Flügge) is the predominant forage grass utilized by the beef cattle industry in southern Georgia, southern Alabama and throughout Florida. Bahiagrass’s popularity is attributed to its tolerance of marginal soil fertility, establishment by seed, persistence under grazing, long-lived perenniality and its use as either a forage or sod crop. Bahiagrass is native to South America, but has a remarkable naturalization to the southern Coastal Plain environment. Acreage of this species is estimated to cover at least 2.5 million hectares throughout the southeastern United States (Burton, et al. 1997).
Bahiagrass has a number of other important qualities. It is often used in crop rotation because it suppresses many plant parasitic nematodes and soil-borne diseases. Also, unlike most other seed propagated forage crops used in the Southeast, nearly all of the bahiagrass seed that is planted in the Southeast is locally produced. There is a very viable bahiagrass seed industry in the region. Seed characteristics of bahiagrass warrant further efforts to improve its seed yield and reduce the hard seed trait because of slow and, sometimes, unreliable establishment. Breeding efforts targeting improvement of early germination and decreased dormancy in the seed are ongoing at the USDA-ARS Crop Genetics and Breeding Research Unit, Tifton and the University of Florida.
While most bahiagrass varieties, such as ‘Argentine’ and ‘Paraguay 22’ are tetraploid and apomictic, seed from a sexual diploid was collected in northern Argentina and Pensacola, Florida. The Florida population is believed to have made its way to Pensacola through livestock shipments from South America. Dr. Glenn Burton, located at the Forage and Turf Research Unit at Tifton, Georgia began a refined mass selection procedure with the sexual bahiagrass population in the early 1960s (Burton, 1982). He termed the selection procedure Recurrent Restricted Phenotypic Selection (RRPS). Applying this procedure to a base population of ‘Pensacola’ bahiagrass, he selected for increased aboveground yield for nine cycles, which lead to the development of ‘Tifton 9’. Twenty-three cycles of RRPS selection were conducted at the Tifton and remnant seed have been maintained for each population. This unique seed bank offers valuable genetic variability in its populations that have allowed for further genetic studies and potential variety development.
There are several other traits that bahiagrass, if improved, could provide significant impact to the livestock and seed industries of the Southeast. Typically, warm-season grasses are lower in forage quality than cool-season grasses. Bahiagrass is particularly characterized by a seasonal depression in digestibility and increase in fiber concentration, which results in very low forage quality in late summer. This is further complicated by the lack of improvement in quality through management (Burton, et al., 1997). Frequent cutting, for example, provides little opportunity to increase digestibility or reduce fiber concentration. Recent efforts at the USDA-ARS Crop Genetics and Breeding Research Unit, at Tifton, GA have identified individuals with superior IVDMD. Eight cycles of selection for higher IVDMD, utilizing a base population of RRPS Cycle 18 bahiagrass, have resulted in very small, but statistically significant, improvement of mean IVDMD values compared to the unselected population.
Although long-term selection for increased yield of spaced-plants using RRPS has resulted in dramatic increases, it has been accompanied by changes in morphology, which have resulted in more upright plants with less stolon development. A two-year grazing trial at Tifton, using RRPS Cycle 14 bahiagrass, indicated that this upright growth habit impaired stand survival. Another grazing experiment at Tifton, comparing RRPS Cycles 0, 9, 18 and 23, confirmed this response. After one season of hard, continuous grazing, dramatic reduction to the stand occurred in the 2 most advanced cycles. With Tifton 9 (RRPS Cycle 9), the stands declined measurably, but the change was relatively small, comparable to Pensacola bahiagrass (RRPS Cycle 0).
Some of the more recent emphasis on bahiagrass improvement has been in the area of breeding for certain physiological traits, such as photoperiod response and cold tolerance. Low forage production in fall/winter months is a severe limitation for dairy and beef cattle producers in the southeastern U.S. It was hypothesized that short daylengths during these months induce a physiological dormancy in the grass. Recent field experiments conducted at the University of Florida, in conjunction with the USDA-ARS Crop Genetics and Environmental Research Unit, concluded that Pensacola bahiagrass showed especially dramatic increases in forage yield during the fall/winter season when subjected to artificial light to extend the normal daylength. A two-year study with RRPS Cycles 0, 4, Tifton 9 (RRPS Cycle 9) and RRPS Cycle 23 at Quincy, Florida indicated distinct cycle differences in sensitivity to daylength. It further identified individual plants that exhibited day-neutral behavior and significant cold tolerance to temperatures of –40 C.
Because of the popularity of bahiagrass, several southeastern forage breeding programs are targeting areas for forage improvement including cold tolerance, photoperiod response, rapid stand establishment, seedling vigor and forage quality. This coordinated effort, we anticipate, may further improve the adaptation of bahiagrass to the southern U.S., and more specifically, its seasonal productivity in its area of adaptation. This paper provides an overview of the current research on bahiagrass in the southern Coastal Plain region.
Auburn University:
Edzard van Santen (Forage Breeder)
Auburn University has recently approved the release of “AU Sand Mountain” bahiagrass (P. notatum var saure). AU Sand Mountain is the result of a natural selection in a plant introduction thought to have been planted at the Sand Mountain Substation (Crossville, AL) some 30 years ago. The variety has narrow leaves, fine tillers and a short inflorescence. In Alabama, bahiagrass is generally grown in the southern part of the state, generally south of I-85. There, AU-Sand Mountain has out-yielded ‘Pensacola’ and ‘Argentine’ varieties, but yielded less than ‘Tifton 9’. In the northern part of Alabama, this new variety has yielded more than Tifton 9, and even out-yielded bermudagrass. Plans for the new release will include testing and marketing in the more northerly regions of the Southeast. The PVP application is in progress
USDA-ARS Crop Genetics and Breeding Research Unit, Tifton, GA:
Wayne Hanna (Research Geneticist) and Roger Gates (Research Agronomist)
The present emphasis at the Crop Genetics and Breeding Research Unit at Tifton, involves improvement of bahiagrass stand establishment, increased forage digestibility and high yielding performance under heavy grazing pressure.
Experimentation on improved establishment characteristics is based on plant selection within two populations (derived from Tifton 9 and RRPS Cycle 23) for early germination and improved plant persistence. Greenhouse evaluation of germination and emergence indicates improvement due to selection in the Tifton 9 population (not yet reaching performance of Cycle 23). Field comparisons will be needed to confirm the usefulness of this trait.
Seed produced in a polycross of plants from the two populations that survived close continuous grazing were planted in the greenhouse during winter 1999-2000. Resulting selections will be compared, as spaced-plants, to plants from the original base populations. In addition to survival under grazing, the selections will be evaluated for yield and morphological characteristics, particularly stolon development. If substantial improvement in plant persistence is identified, remaining plants will be multiplied and transplanted to an isolation field for seed increase in 2001. Further improvement, if necessary, will be made by additional polycross procedures and repeated evaluation. Plans to continue this effort comparing selected and unselected populations for yield will be made in replicated clipping trials, and for persistence, using heavily grazed small plots in 2002 and 2003.
Improvement of the nutritional value of bahiagrass has been a tedious process. Efforts are continuing on the selection for increased IVDMD. Each year 400 spaced plants are individually harvested and 150 evaluated for IVDMD. Rooted tillers of the16 plants highest in digestibility are excised just before anthesis and maintained in a laboratory polycross to produce seed for the next cycle. Superior plants that were identified in 2000 are now being cloned and will be set out in an isolation block in 2001. Seed harvested from this isolation will be used for a sward test. The sward test will consist of replicated small plots of selected and unselected populations that will be seeded in 2002. Harvests are planned for the two subsequent years to evaluate whether improvement observed in spaced plants can be realized in a sward planting
Ann Blount (Forage Breeder), Ken Quesenberry (Forage Breeder), Paul Mislevy (Research Agronomist), Tom Sinclair (Plant Physiologist), Bob Myer (Animal Nutritionist), Sam Coleman (Animal Nutritionist), Mimi Williams (Research Agronomist), Paul Pfahler (Plant Geneticist), Richard Sprenkel (Entomologist), Jim Rich (Plant Nematologist), and Rex Smith (Molecular Geneticist)
The current effort undertaken at the University of Florida is a multidisciplinary approach to bahiagrass improvement. Strong support from the beef industry sector has prompted a statewide emphasis on bahiagrass variety development. The team approach emphasizes plant improvement in seedling vigor and establishment, cold tolerance, photoperiod response, seasonal distribution of forage production, forage quality, nematode and disease resistances.
Interest in bahiagrass variety improvement in Florida stems from a recent study on the photoperiod response of Pensacola bahiagrass. Findings from the completion of a study in 1997-1999 on the photoperiod sensitivity of several tropical grass species at the University of Florida’s Range Cattle Research and Education Center, Ona, Florida, were recently reported at the XIX International Grasslands Congress in Brazil (Mislevy, et al., 2001) Forage yields were reported on four grasses, including bermudagrass, stargrass and bahiagrass that were subjected to artificial light intended to extend the daylength period in the winter to near normal summer exposure. Swards of the grasses grown under the extended daylength were compared to swards grown under natural shortening daylength during the fall, winter and early spring seasons. Forage yields from that study showed that there were substantial differences among the grasses in the response to the extended daylength. The extended daylength resulted in the greatest forage yield increase for the total fall/winter period in Pensacola bahiagrass (123% 2 yr average or 335 g m-2). Tifton 85 bermudagrass was also responsive to the extended daylength with fall/winter forage yield increases of 45% as a 2 yr average or 370 g m-2.
Based on the Ona findings, vast differences in the photoperiod response was found in bahiagrass, compared to bermudagrass and stargrass. A new experiment was designed to test if genetic differences existed among individual plants in RRPS Cycles 0, 4, Tifton 9 and RRPS Cycle 23. One hundred and seventy five plants, representing each of the four cycles, where started in the greenhouse. Plantlets were split into two ‘clones’ and one set was planted in the field under normal daylength, while its counterpart was planted under artificial lights in the field to maintain a daylength of 15 h. Beginning in August 1999 and continuing through June, 2001, measurements on the foliage growth, flowering, and stolon development have been, and are currently being, collected. First year results from this study supported the Ona trials that bahiagrass was found to be extremely sensitive to shortening daylengths. The study also identified some plants that actually exhibited a day-neutral response and might be of valuable for further genetic and physiological studies.
Along with the photoperiod study at Quincy, a breeding nursery of 20,000 bahiagrass seedlings from RRPS Cycles 0, 4, Tifton 9 and RRPS Cycle 23 was planted and the RRPS procedure was used to select for cold tolerance, late-season forage growth and good stolon development in the populations. Within the field populations, as well as in the photoperiod study, differences were noted for response to daylength and freezing temperatures.
Plant selections were made in Spring, 2000 for high levels of cold tolerance and extremes in behavior for stolon development and top growth. These selections were then planted at Ona and Marianna, FL in Summer, 2000 for further observation. Utilizing the RRPS procedure at Ona and Marianna, rigorous culling of the selections has left a superior population, which will become the basis for the initial polycross program at the University of Florida.
Concurrent with the development of a polycrossing program for variety development, several physiological studies have also been initiated. Plants, which exhibited extremes in growth response and were identified during the first year of the Quincy study, have been vegetatively propagated and planted under artificial light and natural light in a new field study at Ona and in a controlled greenhouse environment at Gainesville. Data on the comparison of the clonal behavior of the selections is not available at this time, however similar trends to what was observed in the Quincy study, are clearly visible.
Another area of related research at University of Florida is the evaluation of other P. notatum accessions and new Paspalum species. A number of plant accessions that are currently available from the National Plant Germplasm System located at Griffin, GA. have been obtained. Accessions have been selected based on their winter survival, foliage yield and seed production at the Griffin location. Paspalum species of particular interest, in addition to new accessions of P. notatum, are P. nicorae, P. guaraniticum, P. guenoarum and P. atratum. Additional seed material has been obtained from CSIRO, Queensland, Australia and from a few tropical grass scientists in Uraguay and northern Argentina. Native Paspalum species have also been collected within the southern Coastal Plain region. Species of particular interest for forage and restoration purposes include P. setaceum, P. vaginatum, P. boscianum, P. floridanum and P. distichum.
Burton, G.W. 1982. Improved recurrent restricted phenotypic selection increases bahiagrass forage yields. Crop Sci. 22:1058-1061.
Burton, G.W., R.N. Gates and G.J. Gasho. 1997. Response of Pensacola Bahiagrass to rates of nitrogen, phosphorus and potassium fertilizers. Soil Crop Sci. Soc. Florida Proc. 56:31-35.
Mislevy, P., T.R. Sinclair and J.D. Ray. 2001. Extended daylength to increase fall/winter yields of warm- season perennial grasses. In: Proc. International Grassl. Congr., XIX, Sao Paulo, Brazil.