Reid Yellow Dent--knob genetics, maturity and yield

--D. M. Steffensen

Open pollinated Reid Yellow Dent has been maintained in isolation at Illinois by D. E. Alexander as have several other classic open pollinated varieties. According to Wallace and Brown (1956) Reid Yellow Dent (RYD) had its origin from the late-maturing Hopkins (a late maturing gourdseed from Virginia) crossed to "Little Yellow," an early flint grown by the Indians in the northeastern U.S. Subsequent selection of Reid contributed significantly to present day dent corn in the Midwest.

For the sake of simplicity let us assume that the RYD (O.P.) population from D. E. Alexander is polymorphic for all of the possible combinations of 4L and 7L knobs. We grew several hundred of these plants and selfed several every day from this "random" population over a thirty day period. The rest were left to open pollinate. However, every plant was scored for the first day of pollen shedding. When these data were plotted, four sharp discontinuous peaks were observed. This is consistent with our cytological observations that RYD has two knobs on 4L and 7L. Extensive analysis of knob genetics of inbred lines of known constitutions such as crosses with B37, B14, B73, Mo17, C103 and crosses to several knobless varieties (Chughtai, 1988, U. of I. thesis, and Steffensen, unpublished) has shown that the earliest plants to flower were knobless or heterozygotes. The next later group to flower were homozygous for one knob pair and knobless or heterozygous for the others and so on to later peaks with 2, 3 and 4 knobs homozygous.

This RYD population was studied to answer three questions: 1) Does homozygosity for knobs (0,1,2 and maybe 3) affect maturity? 2) Does the knob and its bracketing genes have an effect on hybrid vigor when heterozygous? 3) Are successful open pollinated lines maintained by selecting for balanced polymorphism of the knob-gene and knobless gene blocks?

The analysis, so far, indicates that the answers to these three questions will be unambiguous.

First of all, the largest ears are found only in the families with four distinct maturity peaks. Furthermore, the largest ears are only on plants that flower in the earliest peak, indicative of their being heterozygotes for all knob-loci regions.

Most of these and other families have been tested in crosses to known-knob inbred lines (B37, B14, B73, Mo17 and Wilbur's Knobless Flint) for analysis of maturity this spring. Additional crossing in the greenhouse and Molokai between selfed F3 and F4 RYD families will nail down our hybrid vigor conclusions in summer grow-outs.


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