Compatible maize parents for maize x Tripsacum hybridization employing a simplified crossing technique

--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.


Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors

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