Eastern gamagrass, Tripsacum dactyloides (L.), is a highly productive and palatable warm season grass with good prospects as a forage crop. Widespread use, however, has been limited by the following: inadequate seed production, inferior seed quality, difficulties in vegetative establishment, and lack of persistence (Ahring and Frank, J. Range Manage. 21:27-30, 1968). Zea diploperennis, discovered on the threshold of extinction in Jalisco, Mexico (Iltis, Doebley, Guzman and Pazy, Science 203:186-188, 1979), probably owes its survival to the fact that it is a very important source of fodder and is maintained as an integral part of a traditional agroecosystem (Benz, Sánchez-Velásquez; and Santana M., Maydica 35:85-98, 1990). Since T. dactyloides and Z. diploperennis have been successfully crossed to produce fertile hybrids that are prolific seed producers and can be propagated vegetatively, efforts are underway to evaluate the Tripsacum-diploperennis hybrid for use as a forage crop.
Preliminary results of in vitro digestant and nutri-detergent fiber analyses of Zea diploperennis, Zea diploperennis x Tripsacum dactyloides referred to as Sun Dance, Tripsacum dactyloides x Zea diploperennis referred to as Tripsacorn, and Sun Dance x Zea diploperennis, i.e. the diploperennis-Tripsacum hybrid backcrossed to diploperennis, are reported here. For analysis of whole plant, leaf, stem and sheath, several stalks with leaves were collected from individual plants of each of the above designations. Plants were grown in an experimental plot at Duke University during the summer of 1992, and material for analysis harvested in late September of the same year. At harvest, all plants were the same age. Z. diploperennis was in flower, but the hybrids showed no signs of floral initiation. Therefore, although data are not derived from material at comparable physiological stages and are not useful for precise quantitative comparison of forage quality among specimens, it provides valuable qualitative information about fiber content and palatability. Preparatory to processing, plant tissue was freeze-dried and passed through a 1mm sieve in a Wiley mill. Components analyzed include: (1) NDF (neutral detergent fiber), a measure of cell wall; (2) ADF (acid detergent fiber), cell wall after hemicellulose removed; (3) hemi (hemicellulose), NDF/ADF and digestibility is variable; (4) cell, cellulose in cell wall after lignin and soluble ash have been removed; (5) LIG, lignin in cell wall oxidized and washed out, concentration obtained by obtaining difference of value before and after oxidation; (6) ADF-ash, ash left in ADF residue. The values reported in Table 1 are means of duplicate samples.
Table 1. Forage analyses of Tripsacum-diploperennis hybrids.
| NDF | ADF | LIG | ADF-Ash | Cell | Hemi | |
| Leaf | ||||||
| Zea diploperennis (1-2A)* | 58.2 | 29.0 | 3.4 | 1.0 | 24.6 | 29.3 |
| Z. diploperennis (3-7) x T. dactyloides | 61.2 | 30.1 | 2.8 | 1.1 | 26.3 | 31.1 |
| Z. diploperennis (2-3) x T. dactyloides | 58.9 | 29.3 | 2.9 | 1.4 | 25.0 | 29.6 |
| T. dactyloides x Z. diploperennis (3-3) | 60.5 | 29.2 | 5.2 | 0.8 | 23.2 | 31.3 |
| Sun Dance x Z. diploperennis (3-7) | 62.8 | 31.5 | 2.9 | 1.3 | 27.3 | 31.3 |
| Sheath | ||||||
| Zea diploperennis (1-2A)* | 66.3 | 38.8 | 5.5 | 1.4 | 31.9 | 27.6 |
| Z. diploperennis (3-7) x T. dactyloides | 70.5 | 38.9 | 5.6 | 1.4 | 31.9 | 31.6 |
| Z. diploperennis (2-3) x T. dactyloides | 66.1 | 36.1 | 4.9 | 1.5 | 29.8 | 29.9 |
| T. dactyloides x Z. diploperennis (3-3) | 67.2 | 38.0 | 5.4 | 0.9 | 31.7 | 29.1 |
| Sun Dance x Z. diploperennis (3-7) | 63.1 | 34.8 | 6.0 | 1.1 | 27.8 | 28. 3 |
| Stem | ||||||
| Zea diploperennis (1-2A)* | 70.8 | 46.8 | 7.9 | 0.3 | 38.6 | 24.0 |
| Z. diploperennis (3-7) x T. dactyloides | 65.4 | 41.1 | 7.1 | 0.4 | 33.6 | 24.4 |
| Z. diploperennis (2-3) x T. dactyloides | 66.2 | 42.9 | 8.0 | 0.3 | 34.6 | 23.3 |
| T. dactyloides x Z. diploperennis (3-3) | 66.5 | 41.3 | 7.0 | 0.3 | 34.0 | 25.2 |
| Sun Dance x Z. diploperennis (3-7) | 64.1 | 41.6 | 6.4 | 0.2 | 34.9 | 22.8 |
| Whole plant | ||||||
| Zea diploperennis (1-2A)* | 76.1 | 45.2 | 8.7 | 1.7 | 34.9 | 30.9 |
| Z. diploperennis (2-3) x T. dactyloides | 76.2 | 44.7 | 7.5 | 2.6 | 34.5 | 31.5 |
| T. dactyloides x Z. diploperennis (3-3) | 74.6 | 43.0 | 6.9 | 2.1 | 34.0 | 31.6 |
| Sun Dance x Z. diploperennis (3-7) | 75.9 | 44.7 | 6.3 | 2.8 | 35.6 | 31.2 |
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