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Variability of Morphological and Agronomic Traits in Eastern Gamagrass Accessions¹

Eastern gamagrass, Tripsacum dactyloides (L.) L., may have potential for use as a grazed or stored forage if problems with establishment and stand persistence can be reduced and if its nutritive value is high enough to justify the relatively intense management that will likely be necessary for sustained production. In 1979 and 1981, 51 gamagrass accessions, primarily from Texas and Oklahoma were studied in detail near Perkins, Okla. in order to characterize the magnitude of phenotypic variability among them for several agronomic and morphological traits. Most of the accessions had been collected in Texas and Oklahoma. The traits studied were: spring vigor, anthesis date, leaf width, plant height, percent seed set, regrowth vigor, and percent in vitro dry matter digestibility (IVDMD). The IVDMD determinations were made for four sampling dates in 1979 and one sampling date in 1981. The first three 1979 samplings were at intervals of 4 weeks on progressively older plants. The fourth sampling in 1979 and the 1981 sampling were of 5-week old regrowth following a uniform mowing of the nursery. There were highly significant differences (P < 0.01) among the accessions for all traits during each of the 2 years. Years constituted a significant source of variation (P < 0.01) for spring vigor, anthesis date, regrowth vigor, and IVDMD of regrowth forage. Accessions differed significantly (P< 0.01) in IVDMD at each of the four sampling dates in 1979 and the accession by sampling date interaction for IVDMD was also significant(P < 0.01). Accession by year interactions were significant (P < 0.01) for spring vigor, anthesis date, percent seed set, and regrowth vigor. The only partial correlation coefficients that were significantly different from zero were those for vigor of spring growth vs. vigor of regrowth (during both years and for the 2-year mean), and vigor of spring growth vs. plant height (in 1979 and for the 2- year mean). The magnitudes of the ranges among accessions were relatively large for all the traits studied, indicating a wide array of variability that might be used in the genetic manipulation of the species.

Key Words: Tripsacum dactyloides (L.) L. • In vitro dry matter digestibility • Percent seed set • Anthesis date • Spring vigor • Summer regrowth vigor • Leaf width • Plant height

² Former graduate student and professor, Dep. of Agronomy, Oklahoma State Univ., Stillwater, OK 74078; research animal scientist, USDA-SEA-AR, Southern Region, Southwestern Livestock & Forage Res. Stn., El Reno, Okla.

Received for publication May 18, 1982.