--B. Kindiger and J. B. Beckett
Identification of maize stocks that produce viable seed when pollinated by Tripsacum dactyloides L. (L.) should facilitate the transfer of useful Tripsacum germplasm into maize. To this end, a large number of dent stocks, inbred and open pollinated popcorn stocks, popcorn hybrids and popcorn x dent derivatives were pollinated by several diploid and tetraploid T. dactyloides accessions. After preliminary tests, all crosses were made by applying Tripsacum pollen to maize silks in the manner normally used in maize x maize pollinations. However, cutting back was delayed until the silks near the tip of the cob were receptive. In addition, ears were cut back far enough to expose the tip of the cob. The modified technique is not only more efficient but also greatly reduces damage from fungi and insects. Typically, four or five pollinations, utilizing pollen from several 2n and 4n Tripsacum sources, were made in order to rate the quality of hybrid seed produced by each maize stock.
Ears that had 50 or more hybrid kernels with plump endosperm were rated excellent. Ears with plump endosperm but fewer than 50 kernels were rated good. Ears showing less well-developed hybrid seed were rated fair, and ears that failed to produce obvious hybrid seed (because of early abortion) were rated poor.
The table lists the crosses that gave good to excellent hybrid seed
development.
| Maize Parent | Description | Kernel quality |
| Popcorn and popcorn-related stocks | ||
| SG1533 | Population | Excellent x 4n Tripsacum |
| SA194 | Population | Excellent x 4n |
| Germplasm source #1 | Population | Excellent x 4n |
| PI222648 | Population | Excellent x 4n, good x 2n |
| Germplasm source #2 | Population | Excellent x 4n |
| 311254 | Experimental | Excellent x 4n |
| 311255 | Experimental | Excellent x 4n |
| HP303W | Hybrid | Excellent x 4n |
| Sg32 | Inbred | Good x 4n |
| Sg16 | Inbred | Good x 2n & 4n |
| P608 | Hybrid | Good x 4n |
| IaDS53 | Hybrid | Good x 4n |
| PI186206 | Population | Good x 2n & 4n |
| White Cloud | Hybrid | Good x 2n & 4n |
| IADS28 | Hybrid | Good x 4n |
| Ladyfinger Pop | Population | Good x 4n |
| Cornbelt material | ||
| W23* | Inbred | Good x 2n and 4n |
| W23 x Kys | Hybrid | Good x 4n |
| K55 x W23 | Hybrid | Good x 2n and 4n |
| L289 x W23 | Hybrid | Excellent x 4n; good x 2n |
| L289 x N6 | Hybrid | Good x 4n |
*Other tests indicate poorer results in some years
Selected kernels from five popcorn stocks, one popcorn x dent derivative (Germplasm source #2) and two Midwest dent stocks were tested for viability. Complete results are not presented here, but germination ranged from 20% to 96%; six crosses gave at least 50% germination.
In general, it appears that the successful production of viable hybrid
kernels depends primarily on the maize stock used. Within ploidy levels,
differences between Tripsacum sources were not detected. As established
many years ago, 2n maize is much more compatible with 4n Tripsacum
than with 2n Tripsacum.
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