A new mutation affecting tassel and ear morphology
--Laurie G. Smith and Sarah Hake

A recessive inflorescence mutation has been recovered that has some phenotypic similarity to previously described barren stalk and barren inflorescence mutations, but is generally more severe. Though the phenotypic expression of this mutation is somewhat variable, mutant individuals recovered after outcrossing to various inbreds and selfing consistently show a severe reduction in tassel branching and in the production of spikelets in both the tassel and ear. In the most severely affected mutants, the apical inflorescence consists of an elongated, unbranched, bare rachis lacking any floral structures whatsoever, which becomes coiled up to produce a corkscrew-like form (Fig. 1). The effects of the mutation on ear morphology have not been examined in detail, but are similar. The vegetative development of these mutants appears normal, except that severe mutants are dwarfed as adults, perhaps as an indirect consequence of the failure to initiate normal floral development.

 Plants heterozygous for this inflorescence mutation were crossed to dominant barren inflorescence (Bif) mutants; Bif F1 progeny were selfed to generate F2 families segregating both mutant phenotypes. Among F2 families segregating both mutations, three quarters of the plants showed the Bif phenotype (heterozygotes and homozygotes) and one quarter showed the severe bare rachis phenotype described here; no normal individuals were found among a total of 60 F2 individuals scored. This suggests that the new inflorescence mutation is linked, or possibly allelic, to Bif, which has been mapped to 8S. Allelism tests with the recessive barren inflorescence mutations (ba1, ba2, and ba3) have not been done. Two independently derived alleles of this new inflorescence mutation have been recovered from the progeny of self-pollinated individuals with active Mutator transposons; these mutations may therefore be caused by Mu element insertions. Segregating families for these mutations can be made available upon request. 


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