White clover is the most widely used cool-season pasture legume throughout the world due to its aggressive running stems, called stolons, and its excellent reseeding ability. When used as a renovation legume for grass pastures, white clover consistently improves animal performance and, at the same time, limits the use of expensive nitrogen fertilizer.
Within cultivated white clover, there are three distinct, true-breeding types: the small-leaved wild type, the intermediate-leaved common type and the large-leaved ladino type. Most white clover breeding projects in the United States have centered on developing cultivars of ladino white clover. Ladino types are high yielding due to their large leaves and erect growth habit, but possess a low number of stolons compared to the stolon-dense common and wild types. Low stolon density is a primary factor in the poor persistence of ladino cultivars.
White clover ecotypes, defined as plants persisting as an inter-fertile population in the natural environment, were collected in Georgia pastures. These pastures had grass competition and heavy grazing pressure and were even planted previously with ladino cultivars. However, the ecotypes collected were exclusively the stolon-dense common types. Initial experiments demonstrated that this ecotype-based material, including hybrid population crosses of ecotypes with various ladino cultivars, were more persistent than adapted ladino cultivars when established into perennial grasses and grazed with beef cattle. These data indicated that naturalized ecotypes should be used as the base germplasm to increase persistence and performance of white clover under grazing in the southern United States.
Development of Durana and Patriot White Clover
The initial Georgia ecotype collections described above formed the parental base for a breeding program that developed two commercial white clover cultivars, "Durana" and "Patriot." Durana is based strictly on ecotype material. Patriot is a population cross of an ecotype germplasm with the ladino germplasm SRVR.
Both cultivars possessed greater small plot stand survival than the popular ladino cultivar "Regal" under grazing with grass competition (see photos). When inter-seeded into tall fescue pastures, Durana maintained a clover percentage over two years of 43 percent by weight while Regal deteriorated to less than 5 percent by the second year. Beef steer gains on Durana, Regal or grass-alone check pastures (no clover but fertilized with 65 lbs. nitrogen per acre per grazing season) when averaged for both years were as follows: Durana = 2.5, Regal = 2.0 and grass alone = 1.4 lbs. per head per day, respectively. Similar trends were found for Patriot in a separate trial.
From these and other results, it was concluded that both cultivars should be valuable additions for livestock producers in the southeastern U.S. They were both released in 2003, and are now commercially available through Pennington Seed Company.
White Clover for the Southern Great Plains
The questions for us at the Noble Research Institute were now two fold: Will Durana and Patriot have a place in the eastern Oklahoma and Texas region, and will it be possible to use the same ecotype approach to develop white clover cultivars more adapted to the southern Great Plains?
For the first question, grazing persistence trials were established at three locations during 2003 to compare the performance of Durana and Patriot with other cultivars: Haskell, Okla., in cooperation with Oklahoma State University, Ardmore, Okla., at the Noble Research Institute and Overton, Texas, in cooperation with Texas A&M University. These trials will be evaluated this autumn for first-year survival. For the second question, we made ecotype collections in southern Oklahoma and northern Texas. Several experimental cultivars were then developed from these collections, and they will be compared to Durana and Patriot in performance trials currently being established at the Haskell, Ardmore and Overton locations. Survival data will be taken from these trials in the next two years that should answer the question of whether it will be feasible to develop a cultivar more adapted to the region.
Three principles were demonstrated from this research effort. First, the benefit of white clover forage to the total available forage dry matter was shown in increased animal performance over the grass used alone. Second, the poor persistence of ladino cultivars when used in perennial grass-based grazing systems was reconfirmed. Third, the ability of ecotype-based white clover cultivars, specifically Durana and Patriot, to provide better animal performance than ladinos due to increased persistence and ability to sustain a higher clover dry matter percentage was recorded. Durana and Patriot are now valuable additions for livestock producers in the southeastern U.S. It will be interesting to see if these two cultivars will have a place in the southern Great Plains. We will also continue our breeding program to develop a more adapted, ecotype-based cultivar for this region.
Dr. Joe Bouton is director of the Noble Research Institutes Forage Improvement Division.