Indeterminate dwarf: an EMS-induced double mutant

M.G. Neuffer and S. Chao

The indeterminate dwarf mutant, idd*-2286A, reported in MNL63:62 and located (MNL64:52), has exhibited some interesting characteristics. The mutant seedlings are shorter than normal but respond to GA. At the time when normal sibs are mature (60 days) mutant plants are about 1/4 normal height with no evidence of flower formation. At 100 days, mutant plants which are then as tall as normal sibs are still green and growing with approximately 32 leaves and no tassel. As the days become shorter and as a consequence of other still unknown conditions, a heavy tassel with small, culturable plantlets growing from between the glumes appear. Some viable pollen is also produced.

The mutant has been located on the long arm of Chromosome 1 by B-A chromosome tests. A cross with id1 has indicated allelism for the indeterminate aspect but not for dwarfing. Crosses of the mutant with the radiation-induced double mutant, an-6923, which is thought to be deficient for the an1 and bz2 loci, gave a positive allelism test for an1 but negative for bz2. These results suggest that idd*-2286A may be a deficiency for the id1 and the an1 loci and that the order of the genes in question is: centromere, id1, an1, bz2.

As part of an interval mapping project, which is to incorporate all the available visible markers onto the RFLP based map, we have located the mutant segment with reference to RFLP markers using F2 materials generated from idd*-2286A. The preliminary data have indicated the gene order as: centromere - UMC83 - id1 - an1 - bz2. The map distance between UMC83 and id1 is under detailed investigation.

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