indeterminate floral apex1 (ifa1, a.k.a. nuc1) is a recessive mutation that perturbs floral and inflorescence meristems (MNL71:2). Mutant plants often develop extra spikelets per branch in the main inflorescence and more than two flowers form per spikelet. Further, an inflorescence-like structure often develops from the center of the carpel (in ear florets) and at the center of the stamens (in tassel florets). We interpret this phenotype to suggest that ifa1 is required in the suppression or negative regulation of meristem indeterminacy.

To determine the chromosome location of ifa1, we crossed homozygous plants as male to the standard set of waxy-marked reciprocal translocation lines. Non-waxy and waxy kernels from the ears of selfed F1 plants were planted and scored for ifa1 phenotype. Only the F2 progenies of the cross between ifa1 and T1-9c showed evidence of linkage (repulsion): 0/34 ifa1 in waxy plants and 26/78 ifa1 in non-waxy plants. This segregation distortion suggests that ifa1 is on the short arm of chromosome 1.

Several RFLP markers were used to further define the location of ifa1 on chromosome 1S. DNA from 18 plants showing the mutant phenotype was extracted and analyzed for polymorphism. The figure shows the calculated linkage map of these markers with reference to ifa1. No recombination was observed between umc76 and ifa1 out of 36 chromosomes examined.

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