Big rings in corn
--Charles R. Burnham

Goal: a multiple interchange stock, which when crossed with normal, gives a ring of 20. The following multiple interchange stocks have been established:
    1. 1-5-6-7-8, when crossed with N = a ring of 10.
    2. 3-2-4-9-10, when crossed with N = a ring of 10.
    3. 5-7-1-9-10, when crossed with N = a ring of 10.
    4. 6-3-2-4-8, when crossed with N = a ring of 10.
    5. 5-7-1-9-10-8, when crossed with N = a ring of 12.

Stock #1 x #2 = 2 rings of 10. Stock #3 x #4 = 2 rings of 10. Stock #4 x #5 = one ring of 20. I attempted to combine #1 and #2 by crossing #1 x #2 then backcrossing to 1 or 2 and selfing the progeny. Extensive tests were made but no success.

Another approach, using the Mangelsdorf, PC multiple marker stock with one marker in each chromosome from 1-10:bm2, lg1, a1, su, pr, Y or y, gl1, j1, wx, g1, has not been tried.

Cross 1-5-6-7-8 x multiple marker, backcross to 1-5-6-7-8. Self the fertiles, select those segregating for the markers only in chromosomes 3, 2, 4, 9, 10, the chromosomes in the other ring: 3-2-4-9-10. Select those plants homozygous for those markers. Cross the 3-2-4-9-10 stock with the multiple marker stock, backcross to 3-2-4-9-10. Self the fertiles, select ones segregating for markers only in 1, 5, 6, 7, and 8, the chromosomes in the other ring, 1-5-6-7-8. Select those plants homozygous for these markers.

Cross the two stocks: 1-5-6-7-8 a, lg, su, wx, g1 with 3-2-4-9-10 bm1, pr, (Y or y), gl1, j1. The F1s have 2 rings of 10, are more than 95% sterile, and do not shed pollen.

The ideal situation would be for several of the markers in the normal chromosomes in one ring to be closely linked with the interchange break points in the interchange chromosomes in the other ring. This is an application of the scheme used by Inman to construct rings with more chromosomes.

The F1 between the two stocks will have two rings of 10 and the normal chromosomes in each ring will have a genetic marker. Use the F1s for colchicine treatment to study what happens to produce the plants that are about semisterile rather than 95% or more sterile. See Helmy Ghobrial, H's reports in earlier newsletters. Germinating seedlings were watered with a colchicine solution and transplanted to the field. Occasional plants shed pollen. All branches of the plant shed pollen. Also on the few such plants that had tillers all branches also shed pollen. Clues to the explanation should be provided by the genetic markers.

Would the F1 between the two stocks backcrossed to one parent without the markers, followed by selfs, be a method of combining 1-5-6-7-8 with 3-2-4-9-10? 

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