Studies of colchicine- and colcemid-induced fertility in multiple interchange heterozygotes in corn and their F2 and F3

In Newsletter #56, pp. 151-153, one of the partially fertile plants obtained from colcemid-treated seedlings of F1 multiple interchange heterozygotes was reported to have 38 plump seeds. These were from cross A (T3-2-4-9-10 x T1-5-6-7-8). Five of these seeds were planted in the greenhouse in 1982. Three plants were fertile with pollen similar in size to that in normal diploid corn. The other two were similar to their F1 parent, i.e., partially fertile with some 2n-size and some 1n-size pollen. The five plants were selfed and the three fertile ones were testcrossed on normal diploids. Self and testcross progenies were grown in the field in 1982, and sporocytes were collected. Test cross progenies of two of the fertile plants had a ring of ten chromosomes each at diakinesis, neither involving chromosome 6. These, probably, represent one of the original parental combinations. The testcross of the other fertile plant had a ring of four, also not involving chromosome 6. This must be the result of a crossover in one of the differential segments of one of the parental interchanges. The three fertile F2 plants were evidently diploids. Hence some of the pollen produced by the partially fertile F1 parent must have been 1n. Pollen classes b and c in last year's report are probably this type.

All but a few of the remaining F2 seeds and the F3 from selfing the two partially fertile greenhouse plants were planted in the field. Certain plants were fertile with normal-size pollen; others were partially fertile with some large-size pollen as well as normal-size pollen. The degree of fertility in the latter group varied somewhat from plant to plant.

The fertile plants were selfed and testcrossed on both diploid and tetraploid stocks. Crosses on the tetraploid produced only shriveled seeds (probably triploids). Excellent seed and seed set were obtained from the crosses on diploids.

Test crosses of the fertile plants will be grown for cytological examination. It is hoped that one or more of these will have two rings, each with ten chromosomes. This would indicate that the fertile parent was homozygous for the two original parental multiple translocations, T3-2-4-9-10 and T1-5-6-7-8.

Helmy Ghobrial

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

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