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Relative Grazing Preference of Panicum Germplasm from Three Taxa

USDA-ARS, Dep. of Crop Sci. and Dep. of Animal Sci., North Carolina State Univ., Raleigh, NC 27695;
Dep. of Crop Sci., North Carolina State Univ., Raleigh; R.D.
Dep. of Animal Sci., North Carolina State Univ., Raleigh
USDA-ARS, Dep. of Crop Sa., North Carolina State Univ., Raleigh.

^* Corresponding author.

Switchgrass (Panicum virgatum L.) has shown potential in the humid United States for being a valuable livestock feed. Its contribution would be enhanced, however, by improved quality and palatability. The objective of this study was to determine if relative preference differences existed within germplasm of the Panicum taxa. Twenty-four accessions representing three Panicum taxa [Panicum amarum Elliot var. amarum, P. amarum var. amarulum (Hitch. and Chase) P.G. Palmer, and P. virgatum L.] were selected from a collection of 92 naturally occurring accessions based on desirable morphological and quality traits. These accessions represented grazing (G), hay (H), and intermediate (I) morphological types. The eight accessions selected to represent each type varied considerably in morphology. The G and I types evaluated in one experiment and the H types in a second, were established in four replicates on a Cecil clay loam (clayey, kaolinitic, thermic Typic Hapludult) soil. Relative preference scores (1 = least preferred and 10 = most preferred) achieved by defoliation with yearling steers (>BOS taurus) showed a consistent preference difference among accessions within types. The strongest differential in palatability was noted within the G types. Entry #16, the most preferred with a mean rating of 8.1, scored 7 to 10 for 45 out of 48 defoliation opportunities. Entry #13, the least preferred with a mean rating of 3.4, scored 1 to 3 for 31 out of 48 opportunities. Preference was not taxon related. Animal defoliation scores (preference) were not highly correlated (r < 0.60) with in vitro dry matter disappearance, considered the best laboratory index of quality, nor with fiber fraction concentrations or agronomic measurements (canopy height and percent stand). Those entries identified with highest preference in each of the G, I, and H types offer potentially valuable germplasm sources for incorporating desirable traits into switchgrass cultivars. The presence of relatively unpalatable naturally occurring germplasm in the Panicum taxa cautions against indiscriminate use of wild types for agronomic improvement of present cultivars.

Key Words: Switchgrass • Panicum virgatum L. • Panicum amarum var. amarum • In vitro dry matter disappearance • Fiber fractions • Morphological measurements

Received for publication March 23, 1987.